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Android: How to use CountDownLatch?

I have a function that requests data from an api and fills an array list.
Then i use the data from the arraylist in a textView. The problem that occurs is that the function takes time to load the data and the code in which i set the text view gets executed before the arraylist is populated resulting in a crash...I have used Countdown latch to tackle this problem but it isnt working
i have used it wrong most probably.
apirequest function
private void RequestDataFromApi() {
DotaAPIEndpoints textApiService= API_Client.getClient().create(DotaAPIEndpoints.class);
Call<List<Heroes>> call2 =textApiService.getHeroes();
call2.enqueue(new Callback<List<Heroes>>() {
#Override
public void onResponse(Call<List<Heroes>> call, Response<List<Heroes>> response) {
hero_list.clear();
hero_list.addAll(response.body());
}
#Override
public void onFailure(Call<List<Heroes>> call, Throwable t) {
Toast.makeText(MainActivity.this, "hero_list call failed!", Toast.LENGTH_SHORT).show();
}
});
requestLatch.countDown();
}
setText.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
try {
requestLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
textt.setText(hero_list.get(0).getHeroImg());
}
});

setText.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
try {
requestLatch.await();
You cannot call await on the UI thread. Calling await at this point in the above code is telling the UI thread to wait - if the UI thread is waiting, it cannot draw the screen updates, so the system will crash with an Activity Not Responding error.
Perhaps this helps, this is a way to safely allow the button to be clicked and not crash if the data has not loaded yet. (No need for a CountdownLatch at all)
setText.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(hero_list.isEmpty()) {
Toast.makeText(MainActivity.this, "List not ready", Toast.LENGTH_SHORT).show();
return;
}
textt.setText(hero_list.get(0).getHeroImg());
}
});

android asynctask & progress dialog

I'm currently working on a android app in which I use asynctasks to carry out json rest request. I've got this working fine. I have also got a progress dialog being made visible on the preexecute then dismissing it on the postexecute all working fine. see code below.
#Override
protected void onPreExecute(){
Variables var = Variables.getInstance();
Variables.getInstance().showPd(ProgressDialog.show(Variables.getInstance().getContext(), var.getValue("loggingin_text"), var.getValue("pleasewait"), true, false));
}
protected void onPostExecute( JSONObject[] loginresponse ){
Variables.getInstance().dismisspd();
try {
JSONObject responseheader = loginresponse[0].getJSONObject("commonInputParameters");
if (responseheader.getString("status").equals("SUCCESS")) {
Variables.getInstance().setUsername( loginresponse[1].getString("username") );
Variables.getInstance().setSessiontoken(responseheader.getString("userSessionToken"));
delegate.onRequestCompletion( true );
} else {
delegate.onRequestCompletion(false);
}
}catch (JSONException je ) {
this.cancel( true );
}
}
final Button _loginBTN = ( Button ) findViewById(R.id.loginBTN );
_loginBTN.setText( vars.getValue( "loginbtn_text" ) );
_loginBTN.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
final Functions functions = Functions.getInstance();
if( functions.isNetworkAvailable(getApplicationContext())) {
if (functions.fullypopulated(new Object[]{_username, _password})) {
LoginRequest login = new LoginRequest(new responseInterface() {
#Override
public void onRequestCompletion(boolean successfulRequest) {
Variables.getInstance().dismisspd();
if ( !successfulRequest ) {
functions.showDialog(Variables.getInstance().getValue("login_err"), findViewById(R.id.input_username));
functions.clearEditText(new EditText[]{_username, _password});
functions.setError(new EditText[]{_username, _password});
} else {
Intent intent = new Intent(getApplicationContext(), NavigationHandler.class);
startActivity(intent);
finish();
}
}
#Override
public void onRequestCompletion(String requestResponse) {}
#Override
public void onRequestCompletion(int requestResponse) {}
#Override
public void onRequestCompletion(float requestResponse) {}
});
Map<String, String> loginDetails = new HashMap<String, String>();
loginDetails.put("username", _username.getText().toString());
loginDetails.put("password", _password.getText().toString());
login.execute(loginDetails);
} else {
functions.showDialog(Variables.getInstance().getValue("no_details"), findViewById(R.id.input_username));
functions.clearEditText(new EditText[]{_username, _password});
functions.setError(new EditText[]{_username, _password});
}
}
else {
functions.showDialog(Variables.getInstance().getValue("no_network"), findViewById(R.id.input_username));
}
}
});
The problem is that when I try to work in a time out into the async task the progress dialog shows but not until after it has completed and at which point I can't remove it.
This is how I'm trying to run it with a time out.
try{
login.execute(loginDetails).get( 5000, TimeUnit.MILLISECONDS );
}catch (InterruptedException ie ){
}catch (ExecutionException ee){
}catch (TimeoutException te ){
login.cancel(true);
}
Yes I know the catches are empty right now.
UPDATE:
Never mind looking at the get function again, it actually blocks the UI thread that is why the Progress Dialog isn't showing until the ASyncTask has completed. Is there anyway to implement a timeout feature?

Cancelling a task
A task can be cancelled at any time by invoking cancel(boolean). Invoking this method will cause subsequent calls to isCancelled() to return true. After invoking this method, onCancelled(Object), instead of onPostExecute(Object) will be invoked after doInBackground(Object[]) returns.
From http://developer.android.com/reference/android/os/AsyncTask.html
Mind the bold pieces ... as to my understanding, you should dismiss the Dialog in onCancelled() in case of Timeout.

Thread Issue : NullPointerException

I have an issue when I am trying to set text from a last item of a listView into text View which is in the MainActivity. It crashes during running time on “NullPointerException” because I think that that when I’m calling it in MainActivity, It didn’t finish to download on the ListView so when the MainActivity first launched, the listView did not finish his work and the functions getCount(),getItem() and my function getLastElement() are still null.
The issue is that I am not very good with dealing with Thread (Wait(), notify(),..)
Can you please help me with all this?
Here is my code and my LogCat :
public class MainActivity extends Activity implements OnClickListener{
private static Context mContext;
public Button mExit, mHistory, mRating;
public TextView mSignal;
HistoryAdapt myAdapter;
HistoryItems m_myLastItem;
ArrayList<HistoryItems> m_myListItem;
Runnable m_run;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MainActivity.mContext=getApplicationContext();
mExit=(Button)findViewById(R.id.ExitButton);
mExit.setOnClickListener(this);
mHistory=(Button)findViewById(R.id.HistoryButton);
mHistory.setOnClickListener(this);
mRating=(Button)findViewById(R.id.RateButton);
mRating.setOnClickListener(this);
mSignal=(TextView)findViewById(R.id.SignalOfTheDayTV);
//### SET LAST ELEMENT INTO TEXTVIEW
m_myListItem = new ArrayList<HistoryItems>();
myAdapter= new HistoryAdapt(mContext, m_myListItem);
new Thread(
new Runnable(){
#Override
public void run(){
try{
///Need to wait until the data to be downloaded inside HistoryAdapt so it can show the last element from the ListView here
HistoryParser parser = new HistoryParser();
parser.parse(getInputStream(HistoryAct.RSS_LINK));
} catch (XmlPullParserException e) {
Log.w(e.getMessage(), e);
} catch (IOException e) {
Log.w(e.getMessage(), e);
} finally {
//notify that the data finished to download
MainActivity.this.runOnUiThread(
new Runnable(){
public void run(){
m_myLastItem = myAdapter.getLastElement();
//set last signal into TextView
mSignal.setText(m_myLastItem.getTitle());
}
}
);
}
}
}
).run();
//#RATER
// AppRater.app_launched(this);
// AppRater.showRateDialog(this, null);
//Get a Tracker (should auto-report)
((AppManager) getApplication()).getTracker(AppManager.TrackerName.APP_TRACKER);
}//oncreate
private InputStream getInputStream(String link) {
try {
URL url = new URL(link);
return url.openConnection().getInputStream();
} catch (IOException e) {
Log.w(Constants.DATA, "Exception while retrieving the input stream", e);
return null;
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public static Context getAppContext(){
return MainActivity.mContext;
}
public void ExitState(){
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("You're about to quit Signals4Trading");
builder.setIcon(R.drawable.five);
//builder.setMessage("Your device has been registered successfully. You'll receive signals very soon.");
builder.setMessage("Are you sure you want to quit?");
builder.setCancelable(false);//can't click on the background of the activity
builder.setPositiveButton("Yes",new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(),"See you soon", Toast.LENGTH_LONG).show();
finish();
}//OnClickListener PositiveButton
});//anonymous class PositiveButton
builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(),"Enjoy your visit", Toast.LENGTH_LONG).show();
}
});
AlertDialog alertDialog = builder.create();
alertDialog.show();
}//ExitState
public void goToHistoryActivity(){
Intent intent = new Intent(MainActivity.this, HistoryAct.class );
startActivity(intent);
}
public void rateApp(){
Intent intent = new Intent(MainActivity.this, Rate.class);
startActivity(intent);
}
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
switch (v.getId()){
case R.id.ExitButton:
ExitState();
break;
case R.id.HistoryButton:
goToHistoryActivity();
break;
case R.id.RateButton:
rateApp();
break;
}
}
#Override
protected void onStart() {
// TODO Auto-generated method stub
super.onStart();
//Get an Analytics tracker to report app starts & uncaught exceptions etc.
GoogleAnalytics.getInstance(this).reportActivityStart(this);
}
#Override
protected void onStop() {
// TODO Auto-generated method stub
super.onStop();
//Stop the analytics tracking
GoogleAnalytics.getInstance(this).reportActivityStop(this);
}
}//MainActivity
package com.Signals4Trading.push.android;
import java.util.List;
import android.content.Context;
import android.content.Intent;
import android.os.StrictMode;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;
public class HistoryAdapt extends BaseAdapter {
private final List<HistoryItems>items;
private final Context context;
public HistoryAdapt(Context context,List<HistoryItems>items){
this.context=context;
this.items=items;
}//constructor
#Override
public int getCount() {
// TODO Auto-generated method stub
return items.size();
}
#Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return items.get(position);
}
#Override
public long getItemId(int id) {
// TODO Auto-generated method stub
return id;
}
//###FUNCTION THAT RETURN LAST ELEMENT
public HistoryItems getLastElement(){
return items.get(items.size()-1);
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
ViewHolder holder;
if (convertView == null) {
convertView = View.inflate(context, R.layout.historyitems, null);
holder = new ViewHolder();
holder.itemTitle = (TextView) convertView.findViewById(R.id.itemTitleTV);
holder.itemDate=(TextView) convertView.findViewById(R.id.itemDateTV);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
holder.itemTitle.setText(items.get(position).getTitle());
holder.itemDate.setText(items.get(position).getDate());
}
return convertView;
}
class ViewHolder {
TextView itemTitle;
TextView itemDate;
}
}
//HistoryAdapt
11-13 15:18:34.702: E/AndroidRuntime(7737): FATAL EXCEPTION: main
11-13 15:18:34.702: E/AndroidRuntime(7737): Process: com.Signals4Trading.push.android, PID: 7737
11-13 15:18:34.702: E/AndroidRuntime(7737): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.Signals4Trading.push.android/com.Signals4Trading.push.android.MainActivity}:
java.lang.ArrayIndexOutOfBoundsException: length=0; index=-1
11-13 15:18:34.702: E/AndroidRuntime(7737): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)

Your onCreate() call in the Activity is calling:
m_myLastItem= HistoryAdapt.getLastElement();
But, the constructor for HistoryAdapt has not been called yet, and that is where you initialize the static field items within it. I would recommend rethinking this class and its usage as you're using it in an instance manner but have it partially coded as if it is a static class. A good rule of thumb to follow is don't make your static methods dependent on the class being constructed. At that point it's just an instance method.

Looks like you're trying to perform an asynchronous operation using a runnable, then before the asynchronous operation is completed you're trying to use the value it is supposed to set. So I'm assuming you're trying to create a background thread that waits for the data and updates/notifies the UI/UI-thread when it's done loading. This would mean that the asynchronous operation is created and started by the UI-thread during OnCreate and while it is running the UI-thread can happily go on executing the OnCreate method and loading the UI etc.
First of all, it looks like you're creating a runnable but not running it. If you want to run the runnable in a different (asynchronous) thread, try this:
new Thread(
new Runnable()
{
#Override
public void Run()
{
//your code here
}
}
).Run();
*note: Translated this from C#, may not be 100% correct (caps?) but should be really easy to get working.
It's not entirely clear from your code but I assume the code in your runnable fills the HistoryAdapt class with data. Be careful not to create concurrency issues this way. If two threads are trying to access the same object at the same time you may have problems so be sure to properly "lock" objects before using them in seperate threads. In java you can use a "synch" clause to do this:
synchronized(this){
this = newvalue;
}
This makes sure that while the code inside the braces is executing the "this" object cannot be accessed by other threads. Other threads will then wait untill the code is executed and the object is released before continuing.
Secondly, you should be aware that the runnable/thread you've created is basicly a thread that is run once and then disposed (so not a dedicated thread). In this case monitor/wait is not really necessary. You could simply include the code that updates the UI (mSignal.setText(m_myLastItem.getTitle());) in the finally clause of your try/catch statement. Be sure to use the runOnUiThread method when you're trying to update/edit UI-elements from seperate threads like so:
MainActivity.this.runOnUiThread(new Runnable() {
public void run() {
m_myLastItem = HistoryAdapt.getLastElement();
//set last signal into TextView
mSignal.setText(m_myLastItem.getTitle());
}
});
This way, the thread is created in OnCreate, does its job seperately from the UI-thread, then updates the UI as soon as it is done. One possible problem you might have is that mSignal.setText() could get called at a moment when the UI isnt ready to be updated, not sure this will really be a problem in this case though. Also, when using this technique in other places you may need a reference to your activity to use inside your thread (you can't always get a reference from the place where you're defining the thread/runnable), that's easy enough, just make a static reference to your activity somewhere in your app and reference that (i prefer an App_Session class for static variables used app-wide).
Hope I understood the question correctly and this helps. In any case, good luck!
*Edit: Full example
new Thread(
new Runnable()
{
#Override
public void run()
{
if(!HistoryAdapt.hasBeenInitiated)
{
try
{
///Need to wait until the data to be downloaded inside HistoryAdapt so it can show the last element from the ListView here
HistoryParser parser = new HistoryParser();
parser.parse(getInputStream(HistoryAct.RSS_LINK));
} catch (XmlPullParserException e) {
Log.w(e.getMessage(), e);
} catch (IOException e) {
Log.w(e.getMessage(), e);
} finally {
//notify that the data finished to download
MainActivity.this.runOnUiThread(
new Runnable()
{
public void run()
{
if (!HistoryAdapt.hasBeenInitiated)
{
m_myLastItem = HistoryAdapt.getLastElement();
//set last signal into TextView
mSignal.setText(m_myLastItem.getTitle());
}
}
}
);
}
}
}
}
).run();
Could not test this unfortunately since i can't run Java (i use xamarin), should be correct though, maybe the #override isnt needed and im not sure if it's supposed to be 'Run' or 'run'. I'm sure you'll figure that out though ;)

Thread run = new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
}
run = new Thread( new Runnable(){
public void run(){
if(!HistoryAdapt.hasBeenInitiated){
try {
///Need to wait until the data to be downloaded inside HistoryAdapt so it can show the last element from the ListView here
HistoryParser parser = new HistoryParser();
parser.parse(getInputStream(HistoryAct.RSS_LINK));
} catch (XmlPullParserException e) {
Log.w(e.getMessage(), e);
} catch (IOException e) {
Log.w(e.getMessage(), e);
}finally{
//notify that the data finished to download
}
}
}
});
run.start();
run.join();
use this but it will wait until your run thread finish.

Android : Updating UI components from async class

I have UI component where I have table which consist of ImageViews, Now I want to set the image from URL.
Now when I try to call asynchronously the other class where the image is set to UI it gives me error that UI can be updated only by UI thread. I want to load the UI and load images when they are available.
Here is my code :
Calling function...
new AsyncImageLoader(context,imgviewArray).execute();
// Called class..
#Override
protected Void doInBackground(Void... urls) {
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
int i = 0;
try{
db=new MyDB(mainact_instance);
System.out.println("Inside doInBackground");
if(isNetworkAvailable())
{
System.out.println("Network connected");
System.out.println("Fetching from network-Images");
Movie[] movies = db.selectRecords();
for(Movie mv : movies)
{
try {
URL url = new URL(IMAGE_URL+mv.getId()+".jpg");
Bitmap bmp = BitmapFactory.decodeStream(url.openConnection().getInputStream());
images[i].setImageBitmap(bmp);
i++;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
else{
System.out.println("Network not connected..fetching max id row");
}
}catch(Exception ex){ex.printStackTrace();
}
return null;
//db.close();
}
Please tell me how I can I achieve this?

move your UI thread related code to onPostExecute || onProgressUpdate
for example:
protected void onPostExecute(Long result) {
// after finishing fetching your image from URL, update the ImageView here
images[i].setImageBitmap(bmp);
}
I can see you are downloading multiple images inside the AsyncTask then you can use PublishProgress you need to update your AsyncTask definition to allow passing Bitmaps to publishProgress method as follow:
AsyncTask<whatever..., Bitmaps, whatever...>()
Then
publishProgress(yourBitmapObject);
protected void onProgressUpdate(Bitmap[] values) {
images[i].setImageBitmap(values[0]);
};

AsyncTask not displaying onPreExecute

I have two AsyncTask Activities, whose sole responsibilties are to execute an AsyncTask on the UI Thread. One of them works great, displays the progressBar, and updates the ProgressBar message. This is for my SearchActivity, which is actually a search activity with the Google Search metadata for declaring a search activity. I created a clone of the AsyncTask, and only changed doInBackground code, and also clone the SearchActivity and called it browseActivity.
I start BrowseActivity for result in a class that extends listView when an item is clicked. What I intended to happen was for the onPreExecute code of the AsyncTask to display a progressBar as the SearchActivity does, between the ListView activity, and the ResultActivity that the ListView will start onActivityResult. The onPreExcute code is being called but the ProgressBar is never displayed. (I thought I ran it on the UI thread correctly?)
Here is BrowseActivity:
AsyncTask<String, String, ArrayList<SearchResult>> browseTask;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Intent intent = getIntent();
String genreExtra = getIntent().getStringExtra(Genre.BUNDLE_TAG);
if(genreExtra!=null){
genre = Genre.getgenreFromExtra(genreExtra);
}
String categoryExtra = getIntent().getStringExtra(Category.BUNDLE_TAG);
if(categoryExtra!=null){
this.category = Category.getCategoryFromExtra(categoryExtra);
}
final Connector connector = GlobalVars.getCurrentConnector();
Thread browseThread = new Thread(){
#Override
public void run() {
try {
browseTask = connector.browse(BrowseActivity.this, category, genre, 1);
browseTask.execute("");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
runOnUiThread(browseThread);
ArrayList<SearchResult> result = null;
try {
result = browseTask.get();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Bundle queryBundle = new Bundle();
queryBundle.putSerializable(SERIALIZABLE_KEY, result);
Intent i = new Intent();
i.putExtra(BUNDLE_KEY, queryBundle); //Put in our browse results
i.putExtra(Category.BUNDLE_TAG, category.putExtra()); //put our category in return intent
i.putExtra(Genre.BUNDLE_TAG, genre.putExtra()); //put our genre in return intent
setResult(RESULT_OK, i);
finish();
}
Here is the CategoryActivity (extends ListActivity) activity where browseActivity is started:
#Override
protected void onListItemClick(ListView l, View v, final int position, long id) {
super.onListItemClick(l, v, position, id);
Intent i = new Intent(CategorySelectionView.this, BrowseActivity.class);
final Category[] categories = Category.values();
i.putExtra(Category.BUNDLE_TAG, categories[position].putExtra());
i.putExtra(Genre.BUNDLE_TAG, genre.putExtra());
CategorySelectionView.this.startActivityForResult(i, BrowseActivity.RESULT_REQUEST_CODE);
}
// Listen for results.
protected void onActivityResult(int requestCode, int resultCode, Intent data){
// See which child activity is calling us back.
switch (requestCode) {
case BrowseActivity.RESULT_REQUEST_CODE:
// This is the standard resultCode that is sent back if the
// activity crashed or didn't doesn't supply an explicit result.
if (resultCode == RESULT_CANCELED){
}
else {
ArrayList<SearchResult> recentQueryResults = (ArrayList<SearchResult>)data.getBundleExtra(
BrowseActivity.BUNDLE_KEY).getSerializable(BrowseActivity.SERIALIZABLE_KEY);
GlobalVars.setRecentQueryResults(recentQueryResults);
Category category = Category.getCategoryFromExtra(data.getStringExtra(Category.BUNDLE_TAG));
Intent i = new Intent(CategorySelectionView.this, RomListView.class);
i.putExtra(Category.BUNDLE_TAG, category.putExtra());
i.putExtra(Genre.BUNDLE_TAG, genre.putExtra());
startActivity(i);
}
default:
break;
}
}

Firstly, you can't run an AsyncTask on the main/UI Thread, that's the whole point. When you call browseTask.execute() its going to call its methods on the appropriate Thread (main vs background), regardless of calling runOnUiThread(). By calling runOnUiThread() all you are doing is wrapping the code that starts it in another Runnable. I think is not what you want since after calling runOnUiThread() you try to get the result of the task, which hasn't run yet. The code in onCreate() runs on the UI thread, so this has to finish before something else can run, namely the onPreExecute() of the AsyncTask.
What you should be doing is to create the AsyncTask and put everything you currently have after runOnUiThread() in onPostExecute().