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AsyncTask: invalidating view does not take effect

Update
My small showcase is stored on Bitbucket
https://bitbucket.org/solvapps/animationtest
I have an Activity with a view in it. Contentview is set to this view.
public class MainActivity extends AppCompatActivity {
private MyView myView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myView = new MyView(this);
setContentView(myView);
startMovie();
}
public void startMovie(){
MovieTask movieTask = new MovieTask(myView, this);
movieTask.doInBackground(null);
}
}
A MovieTask is an Asynctask and refreshes the view periodically.
But invalidate() doesn't refresh the view.
public class MovieTask extends AsyncTask<String, String, String> {
MyView drawingView;
MainActivity mainActivity;
public MovieTask(MyView view, MainActivity mainActivity){
this.mainActivity = mainActivity;
this.drawingView =view;
}
#Override
protected String doInBackground(String... strings) {
for(int i=20;i<100;i++){
drawingView.myBall.goTo(i,i);
publishProgress();
try {
Thread.sleep(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
return null;
}
#Override
protected void onProgressUpdate(String... values) {
super.onProgressUpdate(values);
mainActivity.runOnUiThread(new Runnable() {
#Override
public void run() {
Log.v("DEBUG_DRAW","in onProgressUpdate()");
drawingView.invalidate();
}
});
}
}
Can someone help ?

See how you are launching the AsyncTask:
public void startMovie() {
MovieTask movieTask = new MovieTask(myView, this);
movieTask.doInBackground(null);
}
You are manually calling a method inside some class called MovieTask, thus you are running a code on the same thread. Obviously, that is not your intention, you intended to run the computation code on a background thread.
Correct way to launch AsyncTask is using execute(Params...):
public void startMovie() {
MovieTask movieTask = new MovieTask(myView, this);
movieTask.execute("");
}
Now you will get the desired effect.
P.S.
Please, do not use that code: you do not need to launch a background thread in order to do that kind of stuff. As an alternative consider Animators API.
Declare setBall(int pos) method inside MyBall class:
public class MyView extends View {
...
public void setBall(int pos) {
myBall.setX(pos);
myBall.setY(pos);
invalidate();
}
}
Then change startMovie() to following:
public void startMovie() {
// "ball" means, that Animators API will search for `public setBall(int)` method inside MyView.java and call that method
ObjectAnimator ball = ObjectAnimator.ofInt(myView, "ball", 20, 100);
ball.setDuration(1000);
ball.start();
}
You'll get the same animation without a nasty code.

There is two possible case, first as described in documents:
void invalidate ()
Invalidate the whole view. If the view is visible,
onDraw(android.graphics.Canvas) will be called at some point in the
future.
So try to run your code in onResume, there is a chance that View is not visible yet.
Secondly View#invalidate tells the system to redraw the view as soon as the main UI thread goes idle. That is, calling invalidate schedules your view to be redrawn after all other immediate work has finished.
If you'd like to have your view updated periodically use Handler#postDelay or run it in a separate thread and use View#postInvalidate to update the View and trigger the call to onDraw.

ANDROID: Update data in another activity in Master Detail Flow Layout

I've searched for a solution for my question all over the internet but I haven't been able to find one and I hope you can help me out
I am trying to create a master detail flow application in android with 2 activities and the second activity contains a fragment. Can anyone please tell me how I can simultaneously update the value in the MainActivity() when I make a change in the fragment's EditText field? I have tried using an Intent but when the 2 activities are side by side that doesnt seem to work well.
Screenshot of Emulator
Any suggestions?

It seems you are in a context as follows:
When A happens, it triggers B
As a result, I suggest you to use EventBus library in your project.
The installation is easy. First, add the following code in your build.gradle file:
compile 'org.greenrobot:eventbus:3.0.0'
Second, let's see what we are going to add in our codes.
In the Fragment which you wanted to make changes:
/* When A happens */
myButton.setOnClickListener(new View.OnClickListener() { // complete entering the content, update it
EventBus.getDefault.post(MyUpdateEvent(myContent));
});
Create your custom class MyUpdateEven:
public class MyUpdateEvent{
private String myContent;
public MyUpdateEvent(String myContent) {
this.myContent = myContent;
}
public String getUpdateContent() {
return myContent;
}
}
In the Activity you wanted to update:
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
EventBus.getDefault.register(this); // add this code to monitor the update
}
/* It triggers B */
#Subscribe // don't forget to add #Subscribe
public void onEvent(MyUpdateEvent event){
// this is your custom method
myTextView.setText(event.getUpdateContent()); // do your update
}
#Override
protected void onDestroy() {
super.onDestroy();
EventBus.getDefault.unregister(this); // when you leave this lifecycle, cancel the monitoring
}
}
EventBus is a good library that I've been used a lot in my projects.
I think it can solve your problem.

Try to define a interface.
public interface OnEditActivity {
public void onEdit(ActivityObject activityObject, boolean isEditing);
}
And on your another class for example DetailActivity, then you have to override the method onEdit that you created in your interface:
public class DetailActivity extends AppCompatActivity implements OnEditActivity{
//IN HERE --- Create method.
#Override
public void onEdit(ActivityObject activityObject, boolean isEditing) {
if(isEditing){
displayView(activityObject,true);
}else{
displayView(activityObject,false);
}
}
}
And in your EditFragment for example will look like this:
public class EditFragment extends Fragment{
//Define your interface in your fragment
private OnEditActivity onEditActivity;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_edit_activity, container, false);
return v;
}
public void onAttach(Activity a) {
super.onAttach(a);
onEditActivity =(OnEditActivity) a;
}
}
And if you want to call onEdit method just call:
onEditActivity.onEdit(activityObjectNew,false)
I hope this help you !

Android the views are reset by orientation the screen [duplicate]

My program does some network activity in a background thread. Before starting, it pops up a progress dialog. The dialog is dismissed on the handler. This all works fine, except when screen orientation changes while the dialog is up (and the background thread is going). At this point the app either crashes, or deadlocks, or gets into a weird stage where the app does not work at all until all the threads have been killed.
How can I handle the screen orientation change gracefully?
The sample code below matches roughly what my real program does:
public class MyAct extends Activity implements Runnable {
public ProgressDialog mProgress;
// UI has a button that when pressed calls send
public void send() {
mProgress = ProgressDialog.show(this, "Please wait",
"Please wait",
true, true);
Thread thread = new Thread(this);
thread.start();
}
public void run() {
Thread.sleep(10000);
Message msg = new Message();
mHandler.sendMessage(msg);
}
private final Handler mHandler = new Handler() {
#Override
public void handleMessage(Message msg) {
mProgress.dismiss();
}
};
}
Stack:
E/WindowManager( 244): Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView#433b7150 that was originally added here
E/WindowManager( 244): android.view.WindowLeaked: Activity MyAct has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView#433b7150 that was originally added here
E/WindowManager( 244): at android.view.ViewRoot.<init>(ViewRoot.java:178)
E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:147)
E/WindowManager( 244): at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:90)
E/WindowManager( 244): at android.view.Window$LocalWindowManager.addView(Window.java:393)
E/WindowManager( 244): at android.app.Dialog.show(Dialog.java:212)
E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:103)
E/WindowManager( 244): at android.app.ProgressDialog.show(ProgressDialog.java:91)
E/WindowManager( 244): at MyAct.send(MyAct.java:294)
E/WindowManager( 244): at MyAct$4.onClick(MyAct.java:174)
E/WindowManager( 244): at android.view.View.performClick(View.java:2129)
E/WindowManager( 244): at android.view.View.onTouchEvent(View.java:3543)
E/WindowManager( 244): at android.widget.TextView.onTouchEvent(TextView.java:4664)
E/WindowManager( 244): at android.view.View.dispatchTouchEvent(View.java:3198)
I have tried to dismiss the progress dialog in onSaveInstanceState, but that just prevents an immediate crash. The background thread is still going, and the UI is in partially drawn state. Need to kill the whole app before it starts working again.

Edit: Google engineers do not recommend this approach, as described by Dianne Hackborn (a.k.a. hackbod) in this StackOverflow post. Check out this blog post for more information.
You have to add this to the activity declaration in the manifest:
android:configChanges="orientation|screenSize"
so it looks like
<activity android:label="#string/app_name"
android:configChanges="orientation|screenSize|keyboardHidden"
android:name=".your.package">
The matter is that the system destroys the activity when a change in the configuration occurs. See ConfigurationChanges.
So putting that in the configuration file avoids the system to destroy your activity. Instead it invokes the onConfigurationChanged(Configuration) method.

When you switch orientations, Android will create a new View. You're probably getting crashes because your background thread is trying to change the state on the old one. (It may also be having trouble because your background thread isn't on the UI thread)
I'd suggest making that mHandler volatile and updating it when the orientation changes.

I came up with a rock-solid solution for these issues that conforms with the 'Android Way' of things. I have all my long-running operations using the IntentService pattern.
That is, my activities broadcast intents, the IntentService does the work, saves the data in the DB and then broadcasts sticky intents. The sticky part is important, such that even if the Activity was paused during during the time after the user initiated the work and misses the real time broadcast from the IntentService we can still respond and pick up the data from the calling Activity. ProgressDialogs can work with this pattern quite nicely with onSaveInstanceState().
Basically, you need to save a flag that you have a progress dialog running in the saved instance bundle. Do not save the progress dialog object because this will leak the entire Activity. To have a persistent handle to the progress dialog, I store it as a weak reference in the application object. On orientation change or anything else that causes the Activity to pause (phone call, user hits home etc.) and then resume, I dismiss the old dialog and recreate a new dialog in the newly created Activity.
For indefinite progress dialogs this is easy. For progress bar style, you have to put the last known progress in the bundle and whatever information you're using locally in the activity to keep track of the progress. On restoring the progress, you'll use this information to re-spawn the progress bar in the same state as before and then update based on the current state of things.
So to summarize, putting long-running tasks into an IntentService coupled with judicious use of onSaveInstanceState() allows you to efficiently keep track of dialogs and restore then across the Activity life-cycle events. Relevant bits of Activity code are below. You'll also need logic in your BroadcastReceiver to handle Sticky intents appropriately, but that is beyond the scope of this.
public void doSignIn(View view) {
waiting=true;
AppClass app=(AppClass) getApplication();
String logingon=getString(R.string.signon);
app.Dialog=new WeakReference<ProgressDialog>(ProgressDialog.show(AddAccount.this, "", logingon, true));
...
}
#Override
protected void onSaveInstanceState(Bundle saveState) {
super.onSaveInstanceState(saveState);
saveState.putBoolean("waiting",waiting);
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState!=null) {
restoreProgress(savedInstanceState);
}
...
}
private void restoreProgress(Bundle savedInstanceState) {
waiting=savedInstanceState.getBoolean("waiting");
if (waiting) {
AppClass app=(AppClass) getApplication();
ProgressDialog refresher=(ProgressDialog) app.Dialog.get();
refresher.dismiss();
String logingon=getString(R.string.signon);
app.Dialog=new WeakReference<ProgressDialog>(ProgressDialog.show(AddAccount.this, "", logingon, true));
}
}

I met the same problem. My activity needs to parse some data from a URL and it's slow. So I create a thread to do so, then show a progress dialog. I let the thread post a message back to UI thread via Handler when it's finished. In Handler.handleMessage, I get the data object (ready now) from thread and populate it to UI. So it's very similar to your example.
After a lot of trial and error it looks like I found a solution. At least now I can rotate screen at any moment, before or after the thread is done. In all tests, the dialog is properly closed and all behaviors are as expected.
What I did is shown below. The goal is to fill my data model (mDataObject) and then populate it to UI. Should allow screen rotation at any moment without surprise.
class MyActivity {
private MyDataObject mDataObject = null;
private static MyThread mParserThread = null; // static, or make it singleton
OnCreate() {
...
Object retained = this.getLastNonConfigurationInstance();
if(retained != null) {
// data is already completely obtained before config change
// by my previous self.
// no need to create thread or show dialog at all
mDataObject = (MyDataObject) retained;
populateUI();
} else if(mParserThread != null && mParserThread.isAlive()){
// note: mParserThread is a static member or singleton object.
// config changed during parsing in previous instance. swap handler
// then wait for it to finish.
mParserThread.setHandler(new MyHandler());
} else {
// no data and no thread. likely initial run
// create thread, show dialog
mParserThread = new MyThread(..., new MyHandler());
mParserThread.start();
showDialog(DIALOG_PROGRESS);
}
}
// http://android-developers.blogspot.com/2009/02/faster-screen-orientation-change.html
public Object onRetainNonConfigurationInstance() {
// my future self can get this without re-downloading
// if it's already ready.
return mDataObject;
}
// use Activity.showDialog instead of ProgressDialog.show
// so the dialog can be automatically managed across config change
#Override
protected Dialog onCreateDialog(int id) {
// show progress dialog here
}
// inner class of MyActivity
private class MyHandler extends Handler {
public void handleMessage(msg) {
mDataObject = mParserThread.getDataObject();
populateUI();
dismissDialog(DIALOG_PROGRESS);
}
}
}
class MyThread extends Thread {
Handler mHandler;
MyDataObject mDataObject;
// constructor with handler param
public MyHandler(..., Handler h) {
...
mHandler = h;
}
public void setHandler(Handler h) { mHandler = h; } // for handler swapping after config change
public MyDataObject getDataObject() { return mDataObject; } // return data object (completed) to caller
public void run() {
mDataObject = new MyDataObject();
// do the lengthy task to fill mDataObject with data
lengthyTask(mDataObject);
// done. notify activity
mHandler.sendEmptyMessage(0); // tell activity: i'm ready. come pick up the data.
}
}
That's what works for me. I don't know if this is the "correct" method as designed by Android -- they claim this "destroy/recreate activity during screen rotation" actually makes things easier, so I guess it shouldn't be too tricky.
Let me know if you see a problem in my code. As said above I don't really know if there is any side effect.

The original perceived problem was that the code would not survive a screen orientation change. Apparently this was "solved" by having the program handle the screen orientation change itself, instead of letting the UI framework do it (via calling onDestroy)).
I would submit that if the underlying problem is that the program will not survive onDestroy(), then the accepted solution is just a workaround that leaves the program with serious other problems and vulnerabilities. Remember that the Android framework specifically states that your activity is at risk for being destroyed almost at any time due to circumstances outside your control. Therefore, your activity must be able to survive onDestroy() and subsequent onCreate() for any reason, not just a screen orientation change.
If you are going to accept handling screen orientation changes yourself to solve the OP's problem, you need to verify that other causes of onDestroy() do not result in the same error. Are you able to do this? If not, I would question whether the "accepted" answer is really a very good one.

My solution was to extend the ProgressDialog class to get my own MyProgressDialog.
I redefined show() and dismiss() methods to lock the orientation before showing the Dialog and unlock it back when Dialog is dismissed.
So when the Dialog is shown and the orientation of the device changes, the orientation of the screen remains until dismiss() is called, then screen-orientation changes according to sensor-values/device-orientation.
Here is my code:
public class MyProgressDialog extends ProgressDialog {
private Context mContext;
public MyProgressDialog(Context context) {
super(context);
mContext = context;
}
public MyProgressDialog(Context context, int theme) {
super(context, theme);
mContext = context;
}
public void show() {
if (mContext.getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT)
((Activity) mContext).setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
else
((Activity) mContext).setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
super.show();
}
public void dismiss() {
super.dismiss();
((Activity) mContext).setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_SENSOR);
}
}

I faced this same problem, and I came up with a solution that didn't invole using the ProgressDialog and I get faster results.
What I did was create a layout that has a ProgressBar in it.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<ProgressBar
android:id="#+id/progressImage"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
/>
</RelativeLayout>
Then in the onCreate method do the following
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.progress);
}
Then do the long task in a thread, and when that's finished have a Runnable set the content view to the real layout you want to use for this activity.
For example:
mHandler.post(new Runnable(){
public void run() {
setContentView(R.layout.my_layout);
}
});
This is what I did, and I've found that it runs faster than showing the ProgressDialog and it's less intrusive and has a better look in my opinion.
However, if you're wanting to use the ProgressDialog, then this answer isn't for you.

I discovered a solution to this that I haven't yet seen elsewhere. You can use a custom application object that knows if you have background tasks going, instead of trying to do this in the activity that gets destroyed and recreated on orientation change. I blogged about this in here.

I going to contribute my approach to handling this rotation issue. This may not be relevant to OP as he's not using AsyncTask, but maybe others will find it useful. It's pretty simple but it seems to do the job for me:
I have a login activity with a nested AsyncTask class called BackgroundLoginTask.
In my BackgroundLoginTask I don't do anything out of the ordinary except to add a null check upon calling ProgressDialog's dismiss:
#Override
protected void onPostExecute(Boolean result)
{
if (pleaseWaitDialog != null)
pleaseWaitDialog.dismiss();
[...]
}
This is to handle the case where the background task finishes while the Activity is not visible and, therefore, the progress dialog has already been dismissed by the onPause() method.
Next, in my parent Activity class, I create global static handles to my AsyncTask class and my ProgressDialog (the AsyncTask, being nested, can access these variables):
private static BackgroundLoginTask backgroundLoginTask;
private static ProgressDialog pleaseWaitDialog;
This serves two purposes: First, it allows my Activity to always access the AsyncTask object even from a new, post-rotated activity. Second, it allows my BackgroundLoginTask to access and dismiss the ProgressDialog even after a rotate.
Next, I add this to onPause(), causing the progress dialog to disappear when our Activity is leaving the foreground (preventing that ugly "force close" crash):
if (pleaseWaitDialog != null)
pleaseWaitDialog.dismiss();
Finally, I have the following in my onResume() method:
if ((backgroundLoginTask != null) && (backgroundLoginTask.getStatus() == Status.RUNNING))
{
if (pleaseWaitDialog != null)
pleaseWaitDialog.show();
}
This allows the Dialog to reappear after the Activity is recreated.
Here is the entire class:
public class NSFkioskLoginActivity extends NSFkioskBaseActivity {
private static BackgroundLoginTask backgroundLoginTask;
private static ProgressDialog pleaseWaitDialog;
private Controller cont;
// This is the app entry point.
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (CredentialsAvailableAndValidated())
{
//Go to main menu and don't run rest of onCreate method.
gotoMainMenu();
return;
}
setContentView(R.layout.login);
populateStoredCredentials();
}
//Save current progress to options when app is leaving foreground
#Override
public void onPause()
{
super.onPause();
saveCredentialsToPreferences(false);
//Get rid of progress dialog in the event of a screen rotation. Prevents a crash.
if (pleaseWaitDialog != null)
pleaseWaitDialog.dismiss();
}
#Override
public void onResume()
{
super.onResume();
if ((backgroundLoginTask != null) && (backgroundLoginTask.getStatus() == Status.RUNNING))
{
if (pleaseWaitDialog != null)
pleaseWaitDialog.show();
}
}
/**
* Go to main menu, finishing this activity
*/
private void gotoMainMenu()
{
startActivity(new Intent(getApplicationContext(), NSFkioskMainMenuActivity.class));
finish();
}
/**
*
* #param setValidatedBooleanTrue If set true, method will set CREDS_HAVE_BEEN_VALIDATED to true in addition to saving username/password.
*/
private void saveCredentialsToPreferences(boolean setValidatedBooleanTrue)
{
SharedPreferences settings = getSharedPreferences(APP_PREFERENCES, MODE_PRIVATE);
SharedPreferences.Editor prefEditor = settings.edit();
EditText usernameText = (EditText) findViewById(R.id.editTextUsername);
EditText pswText = (EditText) findViewById(R.id.editTextPassword);
prefEditor.putString(USERNAME, usernameText.getText().toString());
prefEditor.putString(PASSWORD, pswText.getText().toString());
if (setValidatedBooleanTrue)
prefEditor.putBoolean(CREDS_HAVE_BEEN_VALIDATED, true);
prefEditor.commit();
}
/**
* Checks if user is already signed in
*/
private boolean CredentialsAvailableAndValidated() {
SharedPreferences settings = getSharedPreferences(APP_PREFERENCES,
MODE_PRIVATE);
if (settings.contains(USERNAME) && settings.contains(PASSWORD) && settings.getBoolean(CREDS_HAVE_BEEN_VALIDATED, false) == true)
return true;
else
return false;
}
//Populate stored credentials, if any available
private void populateStoredCredentials()
{
SharedPreferences settings = getSharedPreferences(APP_PREFERENCES,
MODE_PRIVATE);
settings.getString(USERNAME, "");
EditText usernameText = (EditText) findViewById(R.id.editTextUsername);
usernameText.setText(settings.getString(USERNAME, ""));
EditText pswText = (EditText) findViewById(R.id.editTextPassword);
pswText.setText(settings.getString(PASSWORD, ""));
}
/**
* Validate credentials in a seperate thread, displaying a progress circle in the meantime
* If successful, save credentials in preferences and proceed to main menu activity
* If not, display an error message
*/
public void loginButtonClick(View view)
{
if (phoneIsOnline())
{
EditText usernameText = (EditText) findViewById(R.id.editTextUsername);
EditText pswText = (EditText) findViewById(R.id.editTextPassword);
//Call background task worker with username and password params
backgroundLoginTask = new BackgroundLoginTask();
backgroundLoginTask.execute(usernameText.getText().toString(), pswText.getText().toString());
}
else
{
//Display toast informing of no internet access
String notOnlineMessage = getResources().getString(R.string.noNetworkAccessAvailable);
Toast toast = Toast.makeText(getApplicationContext(), notOnlineMessage, Toast.LENGTH_SHORT);
toast.show();
}
}
/**
*
* Takes two params: username and password
*
*/
public class BackgroundLoginTask extends AsyncTask<Object, String, Boolean>
{
private Exception e = null;
#Override
protected void onPreExecute()
{
cont = Controller.getInstance();
//Show progress dialog
String pleaseWait = getResources().getString(R.string.pleaseWait);
String commWithServer = getResources().getString(R.string.communicatingWithServer);
if (pleaseWaitDialog == null)
pleaseWaitDialog= ProgressDialog.show(NSFkioskLoginActivity.this, pleaseWait, commWithServer, true);
}
#Override
protected Boolean doInBackground(Object... params)
{
try {
//Returns true if credentials were valid. False if not. Exception if server could not be reached.
return cont.validateCredentials((String)params[0], (String)params[1]);
} catch (Exception e) {
this.e=e;
return false;
}
}
/**
* result is passed from doInBackground. Indicates whether credentials were validated.
*/
#Override
protected void onPostExecute(Boolean result)
{
//Hide progress dialog and handle exceptions
//Progress dialog may be null if rotation has been switched
if (pleaseWaitDialog != null)
{
pleaseWaitDialog.dismiss();
pleaseWaitDialog = null;
}
if (e != null)
{
//Show toast with exception text
String networkError = getResources().getString(R.string.serverErrorException);
Toast toast = Toast.makeText(getApplicationContext(), networkError, Toast.LENGTH_SHORT);
toast.show();
}
else
{
if (result == true)
{
saveCredentialsToPreferences(true);
gotoMainMenu();
}
else
{
String toastText = getResources().getString(R.string.invalidCredentialsEntered);
Toast toast = Toast.makeText(getApplicationContext(), toastText, Toast.LENGTH_SHORT);
toast.show();
}
}
}
}
}
I am by no means a seasoned Android developer, so feel free to comment.

Move the long task to a seperate class. Implement it as a subject-observer pattern. Whenever the activity is created register and while closing unregister with the task class. Task class can use AsyncTask.

The trick is to show/dismiss the dialog within AsyncTask during onPreExecute/onPostExecute as usual, though in case of orientation-change create/show a new instance of the dialog in the activity and pass its reference to the task.
public class MainActivity extends Activity {
private Button mButton;
private MyTask mTask = null;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
MyTask task = (MyTask) getLastNonConfigurationInstance();
if(task != null){
mTask = task;
mTask.mContext = this;
mTask.mDialog = ProgressDialog.show(this, "", "", true);
}
mButton = (Button) findViewById(R.id.button1);
mButton.setOnClickListener(new View.OnClickListener(){
public void onClick(View v){
mTask = new MyTask(MainActivity.this);
mTask.execute();
}
});
}
#Override
public Object onRetainNonConfigurationInstance() {
String str = "null";
if(mTask != null){
str = mTask.toString();
mTask.mDialog.dismiss();
}
Toast.makeText(this, str, Toast.LENGTH_SHORT).show();
return mTask;
}
private class MyTask extends AsyncTask<Void, Void, Void>{
private ProgressDialog mDialog;
private MainActivity mContext;
public MyTask(MainActivity context){
super();
mContext = context;
}
protected void onPreExecute() {
mDialog = ProgressDialog.show(MainActivity.this, "", "", true);
}
protected void onPostExecute(Void result) {
mContext.mTask = null;
mDialog.dismiss();
}
#Override
protected Void doInBackground(Void... params) {
SystemClock.sleep(5000);
return null;
}
}
}

I have done it like this:
package com.palewar;
import android.app.Activity;
import android.app.ProgressDialog;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
public class ThreadActivity extends Activity {
static ProgressDialog dialog;
private Thread downloadThread;
final static Handler handler = new Handler() {
#Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
dialog.dismiss();
}
};
protected void onDestroy() {
super.onDestroy();
if (dialog != null && dialog.isShowing()) {
dialog.dismiss();
dialog = null;
}
}
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
downloadThread = (Thread) getLastNonConfigurationInstance();
if (downloadThread != null && downloadThread.isAlive()) {
dialog = ProgressDialog.show(ThreadActivity.this, "",
"Signing in...", false);
}
dialog = ProgressDialog.show(ThreadActivity.this, "",
"Signing in ...", false);
downloadThread = new MyThread();
downloadThread.start();
// processThread();
}
// Save the thread
#Override
public Object onRetainNonConfigurationInstance() {
return downloadThread;
}
static public class MyThread extends Thread {
#Override
public void run() {
try {
// Simulate a slow network
try {
new Thread().sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
handler.sendEmptyMessage(0);
} finally {
}
}
}
}
You can also try and let me know it works for you or not

This is my proposed solution:
Move the AsyncTask or Thread to a retained Fragment, as explained here. I believe it is a good practice to move all network calls to fragments. If you are already using fragments, one of them could be made responsible for the calls. Otherwise, you can create a fragment just for doing the request, as the linked article proposes.
The fragment will use a listener interface to signal the task completion/failure. You don't have to worry for orientation changes there. The fragment will always have the correct link to the current activity and progress dialog can be safely resumed.
Make your progress dialog a member of your class. In fact you should do that for all dialogs. In the onPause method you should dismiss them, otherwise you will leak a window on the configuration change. The busy state should be kept by the fragment. When the fragment is attached to the activity, you can bring up the progress dialog again, if the call is still running. A void showProgressDialog() method can be added to the fragment-activity listener interface for this purpose.

If you create a background Service that does all the heavy lifting (tcp requests/response, unmarshalling), the View and Activity can be destroyed and re-created without leaking window or losing data. This allows the Android recommended behavior, which is to destroy an Activity on each configuration change (eg. for each orientation change).
It is a bit more complex, but it is the best way for invoking server request, data pre/post-processing, etc.
You may even use your Service to queue each request to a server, so it makes it easy and efficient to handle those things.
The dev guide has a full chapter on Services.

I have an implementation which allows the activity to be destroyed on a screen orientation change, but still destroys the dialog in the recreated activity successfully.
I use ...NonConfigurationInstance to attach the background task to the recreated activity.
The normal Android framework handles recreating the dialog itself, nothing is changed there.
I subclassed AsyncTask adding a field for the 'owning' activity, and a method to update this owner.
class MyBackgroundTask extends AsyncTask<...> {
MyBackgroundTask (Activity a, ...) {
super();
this.ownerActivity = a;
}
public void attach(Activity a) {
ownerActivity = a;
}
protected void onPostExecute(Integer result) {
super.onPostExecute(result);
ownerActivity.dismissDialog(DIALOG_PROGRESS);
}
...
}
In my activity class I added a field backgroundTask referring to the 'owned' backgroundtask, and I update this field using onRetainNonConfigurationInstance and getLastNonConfigurationInstance.
class MyActivity extends Activity {
public void onCreate(Bundle savedInstanceState) {
...
if (getLastNonConfigurationInstance() != null) {
backgroundTask = (MyBackgroundTask) getLastNonConfigurationInstance();
backgroundTask.attach(this);
}
}
void startBackgroundTask() {
backgroundTask = new MyBackgroundTask(this, ...);
showDialog(DIALOG_PROGRESS);
backgroundTask.execute(...);
}
public Object onRetainNonConfigurationInstance() {
if (backgroundTask != null && backgroundTask.getStatus() != Status.FINISHED)
return backgroundTask;
return null;
}
...
}
Suggestions for further improvement:
Clear the backgroundTask reference in the activity after the task is finished to release any memory or other resources associated with it.
Clear the ownerActivity reference in the backgroundtask before the activity is destroyed in case it will not be recreated immediately.
Create a BackgroundTask interface and/or collection to allow different types of tasks to run from the same owning activity.

If you maintain two layouts, all UI thread should be terminated.
If you use AsynTask, then you can easily call .cancel() method inside onDestroy() method of current activity.
#Override
protected void onDestroy (){
removeDialog(DIALOG_LOGIN_ID); // remove loading dialog
if (loginTask != null){
if (loginTask.getStatus() != AsyncTask.Status.FINISHED)
loginTask.cancel(true); //cancel AsyncTask
}
super.onDestroy();
}
For AsyncTask, read more in "Cancelling a task" section at here.
Update:
Added condition to check status, as it can be only cancelled if it is in running state.
Also note that the AsyncTask can only be executed one time.

Tried to implement jfelectron's solution because it is a "rock-solid solution to these issues that conforms with the 'Android Way' of things" but it took some time to look up and put together all the elements mentioned. Ended up with this slightly different, and I think more elegant, solution posted here in it's entirety.
Uses an IntentService fired from an activity to perform the long running task on a separate thread. The service fires back sticky Broadcast Intents to the activity which update the dialog. The Activity uses showDialog(), onCreateDialog() and onPrepareDialog() to eliminate the need to have persistent data passed in the application object or the savedInstanceState bundle. This should work no matter how your application is interrupted.
Activity Class:
public class TesterActivity extends Activity {
private ProgressDialog mProgressDialog;
private static final int PROGRESS_DIALOG = 0;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Button b = (Button) this.findViewById(R.id.test_button);
b.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
buttonClick();
}
});
}
private void buttonClick(){
clearPriorBroadcast();
showDialog(PROGRESS_DIALOG);
Intent svc = new Intent(this, MyService.class);
startService(svc);
}
protected Dialog onCreateDialog(int id) {
switch(id) {
case PROGRESS_DIALOG:
mProgressDialog = new ProgressDialog(TesterActivity.this);
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setMax(MyService.MAX_COUNTER);
mProgressDialog.setMessage("Processing...");
return mProgressDialog;
default:
return null;
}
}
#Override
protected void onPrepareDialog(int id, Dialog dialog) {
switch(id) {
case PROGRESS_DIALOG:
// setup a broadcast receiver to receive update events from the long running process
IntentFilter filter = new IntentFilter();
filter.addAction(MyService.BG_PROCESS_INTENT);
registerReceiver(new MyBroadcastReceiver(), filter);
break;
}
}
public class MyBroadcastReceiver extends BroadcastReceiver{
#Override
public void onReceive(Context context, Intent intent) {
if (intent.hasExtra(MyService.KEY_COUNTER)){
int count = intent.getIntExtra(MyService.KEY_COUNTER, 0);
mProgressDialog.setProgress(count);
if (count >= MyService.MAX_COUNTER){
dismissDialog(PROGRESS_DIALOG);
}
}
}
}
/*
* Sticky broadcasts persist and any prior broadcast will trigger in the
* broadcast receiver as soon as it is registered.
* To clear any prior broadcast this code sends a blank broadcast to clear
* the last sticky broadcast.
* This broadcast has no extras it will be ignored in the broadcast receiver
* setup in onPrepareDialog()
*/
private void clearPriorBroadcast(){
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(MyService.BG_PROCESS_INTENT);
sendStickyBroadcast(broadcastIntent);
}}
IntentService Class:
public class MyService extends IntentService {
public static final String BG_PROCESS_INTENT = "com.mindspiker.Tester.MyService.TEST";
public static final String KEY_COUNTER = "counter";
public static final int MAX_COUNTER = 100;
public MyService() {
super("");
}
#Override
protected void onHandleIntent(Intent intent) {
for (int i = 0; i <= MAX_COUNTER; i++) {
Log.e("Service Example", " " + i);
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
Intent broadcastIntent = new Intent();
broadcastIntent.setAction(BG_PROCESS_INTENT);
broadcastIntent.putExtra(KEY_COUNTER, i);
sendStickyBroadcast(broadcastIntent);
}
}}
Manifest file entries:
before application section:
uses-permission android:name="com.mindspiker.Tester.MyService.TEST"
uses-permission android:name="android.permission.BROADCAST_STICKY"
inside application section
service android:name=".MyService"

I faced the same situation. What I did was get only one instance for my progress dialog in the entire application.
First, I created a DialogSingleton class to get only one instance (Singleton pattern)
public class DialogSingleton
{
private static Dialog dialog;
private static final Object mLock = new Object();
private static DialogSingleton instance;
private DialogSingleton()
{
}
public static DialogSingleton GetInstance()
{
synchronized (mLock)
{
if(instance == null)
{
instance = new DialogSingleton();
}
return instance;
}
}
public void DialogShow(Context context, String title)
{
if(!((Activity)context).isFinishing())
{
dialog = new ProgressDialog(context, 2);
dialog.setCanceledOnTouchOutside(false);
dialog.setTitle(title);
dialog.show();
}
}
public void DialogDismiss(Context context)
{
if(!((Activity)context).isFinishing() && dialog.isShowing())
{
dialog.dismiss();
}
}
}
As I show in this class, I have the progress dialog as attribute. Every time I need to show a progress dialog, I get the unique instance and create a new ProgressDialog.
DialogSingleton.GetInstance().DialogShow(this, "My title here!");
When I am done with the background task, I call again the unique instance and dismiss its dialog.
DialogSingleton.GetInstance().DialogDismiss(this);
I save the background task status in my shared preferences. When I rotate the screen, I ask if I have a task running for this activity: (onCreate)
if(Boolean.parseBoolean(preference.GetValue(IS_TASK_NAME_EXECUTED_KEY, "boolean").toString()))
{
DialogSingleton.GetInstance().DialogShow(this, "Checking credentials!");
} // preference object gets the info from shared preferences (my own implementation to get and put data to shared preferences) and IS_TASK_NAME_EXECUTED_KEY is the key to save this flag (flag to know if this activity has a background task already running).
When I start running a background task:
preference.AddValue(IS_TASK_NAME_EXECUTED_KEY, true, "boolean");
DialogSingleton.GetInstance().DialogShow(this, "My title here!");
When I finish running a background task:
preference.AddValue(IS_TASK_NAME_EXECUTED_KEY, false, "boolean");
DialogSingleton.GetInstance().DialogDismiss(ActivityName.this);
I hope it helps.

This is a very old question that came up on the sidebar for some reason.
If the background task only needs to survive while the activity is in the foreground, the "new" solution is to host the background thread (or, preferably, AsyncTask) in a retained fragment, as described in this developer guide and numerous Q&As.
A retained fragment survives if the activity is destroyed for a configuration change, but not when the activity is destroyed in the background or back stack. Therefore, the background task should still be interrupted if isChangingConfigurations() is false in onPause().

I am a fresher in android and I tried this and it's worked.
public class loadTotalMemberByBranch extends AsyncTask<Void, Void,Void> {
ProgressDialog progressDialog = new ProgressDialog(Login.this);
int ranSucess=0;
#Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();
progressDialog.setTitle("");
progressDialog.isIndeterminate();
progressDialog.setCancelable(false);
progressDialog.show();
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_NOSENSOR);
}
#Override
protected Void doInBackground(Void... params) {
// TODO Auto-generated method stub
return null;
}
#Override
protected void onPostExecute(Void result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
progressDialog.dismiss();
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_NOSENSOR);
}
}

I've tried EVERYTHING. Spent days experimenting. I didn't want to block the activity from rotating. My scenario was:
A progress dialog showing dynamic information to the user. E.g.: "Connecting to server...", "Downloading data...", etc.
A thread doing the heavy stuff and updating the dialog
Updating the UI with the results at the end.
The problem was, when rotating the screen, every solution on the book failed. Even with the AsyncTask class, which is the correct Android way of dealing with this situations. When rotating the screen, the current Context that the starting thread is working with, is gone, and that messes up with the dialog that is showing. The problem was always the Dialog, no matter how many tricks I added to the code (passing new contexts to running threads, retaining thread states through rotations, etc...). The code complexity at the end was always huge and there was always something that could go wrong.
The only solution that worked for me was the Activity/Dialog trick. It's simple and genius and it's all rotation proof:
Instead of creating a Dialog and ask to show it, create an Activity that has been set in the manifest with android:theme="#android:style/Theme.Dialog". So, it just looks like a dialog.
Replace showDialog(DIALOG_ID) with startActivityForResult(yourActivityDialog, yourCode);
Use onActivityResult in the calling Activity to get the results from the executing thread (even the errors) and update the UI.
On your 'ActivityDialog', use threads or AsyncTask to execute long tasks and onRetainNonConfigurationInstance to save "dialog" state when rotating the screen.
This is fast and works fine. I still use dialogs for other tasks and the AsyncTask for something that doesn't require a constant dialog on screen. But with this scenario, I always go for the Activity/Dialog pattern.
And, I didn't try it, but it's even possible to block that Activity/Dialog from rotating, when the thread is running, speeding things up, while allowing the calling Activity to rotate.

These days there is a much more distinct way to handle these types of issues. The typical approach is:
1. Ensure your data is properly seperated from the UI:
Anything that is a background process should be in a retained Fragment (set this with Fragment.setRetainInstance(). This becomes your 'persistent data storage' where anything data based that you would like retained is kept. After the orientation change event, this Fragment will still be accessible in its original state through a FragmentManager.findFragmentByTag() call (when you create it you should give it a tag not an ID as it is not attached to a View).
See the Handling Runtime Changes developed guide for information about doing this correctly and why it is the best option.
2. Ensure you are interfacing correctly and safely between the background processs and your UI:
You must reverse your linking process. At the moment your background process attaches itself to a View - instead your View should be attaching itself to the background process. It makes more sense right? The View's action is dependent on the background process, whereas the background process is not dependent on the View.This means changing the link to a standard Listener interface. Say your process (whatever class it is - whether it is an AsyncTask, Runnable or whatever) defines a OnProcessFinishedListener, when the process is done it should call that listener if it exists.
This answer is a nice concise description of how to do custom listeners.
3. Link your UI into the data process whenever the UI is created (including orientation changes):
Now you must worry about interfacing the background task with whatever your current View structure is. If you are handling your orientation changes properly (not the configChanges hack people always recommend), then your Dialog will be recreated by the system. This is important, it means that on the orientation change, all your Dialog's lifecycle methods are recalled. So in any of these methods (onCreateDialog is usually a good place), you could do a call like the following:
DataFragment f = getActivity().getFragmentManager().findFragmentByTag("BACKGROUND_TAG");
if (f != null) {
f.mBackgroundProcess.setOnProcessFinishedListener(new OnProcessFinishedListener() {
public void onProcessFinished() {
dismiss();
}
});
}
See the Fragment lifecycle for deciding where setting the listener best fits in your individual implementation.
This is a general approach to providing a robust and complete solution to the generic problem asked in this question. There is probably a few minor pieces missing in this answer depending on your individual scenario, but this is generally the most correct approach for properly handling orientation change events.

i have found and easier solution to handle threads when orientation change. You can just keep an static reference to your activity/fragment and verify if its null before acting on the ui. I suggest using a try catch too:
public class DashListFragment extends Fragment {
private static DashListFragment ACTIVE_INSTANCE;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ACTIVE_INSTANCE = this;
new Handler().postDelayed(new Runnable() {
public void run() {
try {
if (ACTIVE_INSTANCE != null) {
setAdapter(); // this method do something on ui or use context
}
}
catch (Exception e) {}
}
}, 1500l);
}
#Override
public void onDestroy() {
super.onDestroy();
ACTIVE_INSTANCE = null;
}
}

If you're struggling with detecting orientation change events of a dialog INDEPENDENT OF AN ACTIVITY REFERENCE, this method works excitingly well. I use this because I have my own dialog class that can be shown in multiple different Activities so I don't always know which Activity it's being shown in. With this method you don't need to change the AndroidManifest, worry about Activity references, and you don't need a custom dialog (as I have). You do need, however, a custom content view so you can detect the orientation changes using that particular view. Here's my example:
Setup
public class MyContentView extends View{
public MyContentView(Context context){
super(context);
}
#Override
public void onConfigurationChanged(Configuration newConfig){
super.onConfigurationChanged(newConfig);
//DO SOMETHING HERE!! :D
}
}
Implementation 1 - Dialog
Dialog dialog = new Dialog(context);
//set up dialog
dialog.setContentView(new MyContentView(context));
dialog.show();
Implementation 2 - AlertDialog.Builder
AlertDialog.Builder builder = new AlertDialog.Builder(context);
//set up dialog builder
builder.setView(new MyContentView(context)); //Can use this method
builder.setCustomTitle(new MycontentView(context)); // or this method
builder.build().show();
Implementation 3 - ProgressDialog / AlertDialog
ProgressDialog progress = new ProgressDialog(context);
//set up progress dialog
progress.setView(new MyContentView(context)); //Can use this method
progress.setCustomTitle(new MyContentView(context)); // or this method
progress.show();

This is my solution when I faced it:
ProgressDialog is not a Fragment child, so my custom class "ProgressDialogFragment" can extend DialogFragment instead in order to keep the dialog shown for configuration changes.
import androidx.annotation.NonNull;
import android.app.Dialog;
import android.app.ProgressDialog;
import android.os.Bundle;
import androidx.fragment.app.DialogFragment;
import androidx.fragment.app.FragmentManager;
/**
* Usage:
* To display the dialog:
* >>> ProgressDialogFragment.showProgressDialogFragment(
* getSupportFragmentManager(),
* "fragment_tag",
* "my dialog title",
* "my dialog message");
*
* To hide the dialog
* >>> ProgressDialogFragment.hideProgressDialogFragment();
*/
public class ProgressDialogFragment extends DialogFragment {
private static String sTitle, sMessage;
private static ProgressDialogFragment sProgressDialogFragment;
public ProgressDialogFragment() {
}
private ProgressDialogFragment(String title, String message) {
sTitle = title;
sMessage = message;
}
#NonNull
#Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
return ProgressDialog.show(getActivity(), sTitle, sMessage);
}
public static void showProgressDialogFragment(FragmentManager fragmentManager, String fragmentTag, String title, String message) {
if (sProgressDialogFragment == null) {
sProgressDialogFragment = new ProgressDialogFragment(title, message);
sProgressDialogFragment.show(fragmentManager, fragmentTag);
} else { // case of config change (device rotation)
sProgressDialogFragment = (ProgressDialogFragment) fragmentManager.findFragmentByTag(fragmentTag); // sProgressDialogFragment will try to survive its state on configuration as much as it can, but when calling .dismiss() it returns NPE, so we have to reset it on each config change
sTitle = title;
sMessage = message;
}
}
public static void hideProgressDialogFragment() {
if (sProgressDialogFragment != null) {
sProgressDialogFragment.dismiss();
}
}
}
The challenge was to retain the dialog title & message while screen
rotation as they reset to the default empty string, although the dialog still shown
There are 2 approaches to solve this:
First approach:
Make the activity that utilizes the dialog to retain state during config change in manifest file:
android:configChanges="orientation|screenSize|keyboardHidden"
This approach is not preferred by Google.
Second approach:
on the activity's onCreate() method, you need to retain your DialogFragment by rebuilding the ProgressDialogFragment again with the title & message as follows if the savedInstanceState is not null:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_deal);
if (savedInstanceState != null) {
ProgressDialogFragment saveProgressDialog = (ProgressDialogFragment) getSupportFragmentManager()
.findFragmentByTag("fragment_tag");
if (saveProgressDialog != null) {
showProgressDialogFragment(getSupportFragmentManager(), "fragment_tag", "my dialog title", "my dialog message");
}
}
}

Seems far too 'quick and dirty' to be true so please point out the flaws but what I found worked was...
Within the onPostExecute method of my AsyncTask, I simply wrapped the '.dismiss' for the progress dialog in a try/catch block (with an empty catch) and then simply ignored the exception that was raised. Seems wrong to do but appears there are no ill effects (at least for what I am doing subsequently which is to start another activity passing in the result of my long running query as an Extra)

The simplest and most flexible solution is to use an AsyncTask with a static reference to ProgressBar. This provides an encapsulated and thus reusable solution to orientation change problems. This solution has served me well for varying asyncronous tasks including internet downloads, communicating with Services, and filesystem scans. The solution has been well tested on multiple android versions and phone models. A complete demo can be found here with specific interest in DownloadFile.java
I present the following as a concept example
public class SimpleAsync extends AsyncTask<String, Integer, String> {
private static ProgressDialog mProgressDialog = null;
private final Context mContext;
public SimpleAsync(Context context) {
mContext = context;
if ( mProgressDialog != null ) {
onPreExecute();
}
}
#Override
protected void onPreExecute() {
mProgressDialog = new ProgressDialog( mContext );
mProgressDialog.show();
}
#Override
protected void onPostExecute(String result) {
if ( mProgressDialog != null ) {
mProgressDialog.dismiss();
mProgressDialog = null;
}
}
#Override
protected void onProgressUpdate(Integer... progress) {
mProgressDialog.setProgress( progress[0] );
}
#Override
protected String doInBackground(String... sUrl) {
// Do some work here
publishProgress(1);
return null;
}
public void dismiss() {
if ( mProgressDialog != null ) {
mProgressDialog.dismiss();
}
}
}
Usage in an Android Activity is simple
public class MainActivity extends Activity {
DemoServiceClient mClient = null;
DownloadFile mDownloadFile = null;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate( savedInstanceState );
setContentView( R.layout.main );
mDownloadFile = new DownloadFile( this );
Button downloadButton = (Button) findViewById( R.id.download_file_button );
downloadButton.setOnClickListener( new View.OnClickListener() {
#Override
public void onClick(View view) {
mDownloadFile.execute( "http://www.textfiles.com/food/bakebred.txt");
}
});
}
#Override
public void onPause() {
super.onPause();
mDownloadFile.dismiss();
}
}

When you change orientations , Android kill that activity and created new activity .
I suggest to use retrofit with Rx java . which handle crashes automatically .
Use these method when retrofit call.
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())

AsyncTask is restarting when i press back button

I have an activity with multiple AsyncTask's, but when i press back button, the Activity is reloaded and the AsyncTask's are executed again. what should i do to Back to the previous activity and not reload the activity and asynctask ? please help.
public class LugarActivity extends SherlockActivity {
CargarDatos cargarDatos;
CargarComentarios cargarComentarios;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_lugar);
cargarDatos = new CargarDatos();
cargarCometarios = new CargarComentarios();
loadData();
}
public void loadData(){
cargarDatos.execute();
}
public void loadOtherData(){
cargarComentarios.execute();
}
public class CargarDatos extends AsyncTask<Integer, Integer, String>{
#Override
protected String doInBackground(Integer... params) {
// here download data
}
#Override
protected void onPostExecute(String html) {
loadOtherData();
}
}
public class CargarComentarios extends AsyncTask<Integer, Integer, String>{
#Override
protected String doInBackground(Integer... params) {
// here download data
}
}
}
FIXED!
i fixed the problem with Singleton class:
public class DataManager {
private static DataManager instance = null;
protected static boolean isShowingTheView = false;
protected DataManager() { }
public static synchronized DataManager getInstance() {
if (instance == null) {
instance = new DataManager();
}
return instance;
}
}
in the activity i add this code:
DataManager dataManager = new DataManager();
if(!dataManager.isShowingTheView){
loadData();
dataManager.isShowingTheView = true;
}else{
finish();
}
and finally i override the onDestroy() method
#Override
public void onDestroy(){
dataManager.isShowingTheView = false;
super.onDestroy();
}

Remove loadData() from onCreate and call somewhere else.

Use Fragments
http://www.androiddesignpatterns.com/2013/04/retaining-objects-across-config-changes.html
A fragment can stay in memory during a configuration change and therefore you can run your asynctask inside itself. You can then query the fragment for any state information you require from your tasks and update your Activity accordingly.

If your Activity is destroyed before the other activity starts, using the back button will call onCreate again, instead of onRestart or onResume.
See here for details.
As Kuffs already mentions, using Fragments is the way to go.
Uglier solution, you could also set a shared preference holding a boolean once your AsyncTask is launched (or on its onPostExecute) so that it won't launch again after checking for that preference on your Activity's onCreate.

Adding AsyncTask class to activity crashes app

I recently needed to use AsyncTask in an activity in my android app. So I made a class inside the activity and extended AsyncTask in that class.
But now, whenever I launch that particular activity, my app immediately crashes. I tried putting the whole onCreate() of the activity in a try, catch block, but no exceptions were raised. The app just crashes immediately when I launch that activity, without any explanation in the LogCat.
This started happening after I added the AsyncTask class mentioned above. Also, the AsyncTask part is NOT executed when the activity is launched, it executes on pressing a button. What could be going wrong? I have added the relevant code below:
public class ListViewA extends Activity{
public void onCreate(Bundle savedInstanceState) {try{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView lv= (ListView)findViewById(R.id.listview);
//computation
}
private String[] top() {
new RetreiveFeedTask().execute(ctr,ctz);
return er;
}
public class RetreiveFeedTask extends AsyncTask<Context, Void, String[]> {
String[] q;
protected String[] doInBackground(Context... params) {
//computation
}
protected void onPostExecute() {
er=q;
gff=true;
}
}
EDIT:
I found an error in LogCat which looks important:
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.exampleapp/com.example.exampleapp.ListViewA}: java.lang.NullPointerException

Your edit is interesting and suggests that there is a problem in the instantiation of the Activity, in which case I would look at the variable declarations quite carefully. However, in the absence of any of that code (or more onCreate code), or the surrounding lines from the logcat, it's hard to be more specific.
As #Raghunandan says, the way your AsynTask is constructed is incorrect, it should be something like:
public class RetreiveFeedTask extends AsyncTask<Context, Void, String[]> {
String[] q;
#Override
protected String[] doInBackground(Context... params) {
//computation
return result; // result is of type String[]
}
protected void onPostExecute(String[] result) {
// do something with result ...
er=q;
gff=true;
}
}
A secondary point is your top() function, which returns er. I am guessing that you want it to wait until the AsyncTask is complete and then return er, which has been calculated by the AsyncTask. However, what it will do at present is to set the AsyncTask and then immediately return er: it won't wait for the AsyncTask to complete.
To achieve that, you probably need to split the button press action into two phases:
Create and run the AsyncTask
OnPostExecute in the AsyncTask calls the code which currently uses the er returned by top.

public class ListViewA extends Activity{
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView lv= (ListView)findViewById(R.id.listview);
//computation
new RetreiveFeedTask().execute(ctr,ctz);
}
...
public class RetreiveFeedTask extends AsyncTask<Context, Void, String[]>{
#Override
protected String[] doInBackground(Context... fileName) {
//computation
String[] q;
//Know that fileName is an Array
return q
}
protected void onPostExecute(String[] result) {
//do something with the result
}
}
...
}

I have a private class ReadFilesTask extends AsyncTask<String, Void, String> in my program. Under that, I have: protected void onPreExecute(),
protected String doInBackground(String... params), and
protected Void onPostExecute(String result).
The first two have #Override above them. The only one I'm ACTUALLY using though, is doInBackground. I'd first really just try adding #Override to doInBackground(). Next, try changing Context to String.
EDIT:
You are also missing the function to grab an activity. Again, this is simply what I'm doing in my code and a few examples I saw online:
public RetreiveFeedTask(Activity activity) {
this.activity = activity;
}
Something like that.