I'm really struggling with a simple issue that I'm hoping someone could assist in .
I have a basic application that authenticates to a database using a basic query.This query is run in the async doinbackground and returns a boolean named isSuccess.
It is then passed to a button onclick method that then determines if the user has entered the correct password. The boolean get reinitialized to true on the async method .
The problem I'm experiencing is that it seems like at the onclick stage it gets the initialised true boolean and not the changed variable value in the indobackground section.
issueing.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v)
{
String passwordd = password.getText().toString();
CheckLogin checkLogin = new CheckLogin();// this is the Asynctask, which is used to process in background to reduce load on app process
checkLogin.execute(passwordd,passwordd);
password.getText().clear();
if (checkLogin.isSuccess)
Toast.makeText(MainActivity.this, "Issue Login", Toast.LENGTH_SHORT).show();
}
});
}
public class CheckLogin extends AsyncTask<String, String, String>
{
String z = "";
boolean isSuccess = true;
#Override
protected void onPreExecute()
{
//progressBar.setVisibility(View.VISIBLE);
}
#Override
protected void onPostExecute(String r)
{
}
#Override
public String doInBackground(String... args)
{
String usernam = args[0];
String passwordd = args[1];
{
try
{
Class.forName("net.sourceforge.jtds.jdbc.Driver");
con = DriverManager.getConnection(db, un, pass); // Connect to database
if (con == null)
{
z = "Check Your Internet Access!";
}
else {
String query = " select * from employee where password = '"+ passwordd+"'" ;
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
String employee,pw;
if (rs.next()) {
employee= rs.getString("employee");
pw = rs.getString("password");
z = "Success";
//setSuccess(true);
isSuccess = true;
}
else if (!rs.next())
{
//setSuccess(false);
//setSuccess(false);
isSuccess = false;
z = "Invalid Password";
}
}
}
catch (Exception ex)
{
isSuccess = false;
//setSuccess(false);
z = ex.getMessage();
}
}
return null;
}
I'm suspecting that the onclick doesn't get the changed boolean value in time because of it running in the background.
This is simply because when you're using the following code:
CheckLogin checkLogin = new CheckLogin();
checkLogin.execute(passwordd,passwordd);
password.getText().clear();
if (checkLogin.isSuccess)
Toast.makeText(MainActivity.this, "Issue Login", Toast.LENGTH_SHORT).show();
}
you're thinking that the code is working in synchronous ways. CheckLogin is an AsyncTask which is working in a asynchronous way. So the CheckLogin code in the following code:
CheckLogin checkLogin = new CheckLogin();
checkLogin.execute(passwordd,passwordd);
will make a separate task and not blocking the process until it finished its job. So, Toast in your following code:
if (checkLogin.isSuccess)
Toast.makeText(MainActivity.this, "Issue Login", Toast.LENGTH_SHORT).show();
}
won't be executed because checkLogin.isSuccess is still false.
The simple fixed is by moving your check to onPostExecute of AsyncTask. Something like this:
#Override
protected void onPostExecute(String r) {
if (checkLogin.isSuccess) {
// do something with the success
}
}
The proper way is by using a listener as a callback mechanism to tell the activity that the process is finished. This will separate your Activity and AsyncTask process to make it more maintainable in the future.
You can use an AsyncTask and callback with something like this:
public class CheckLoginTask extends AsyncTask<Void, Void, Boolean> {
private String mUserName;
private String mPassword;
private ResultListener mListener;
private String mMessage;
public interface ResultListener {
void onSuccess(String message);
void onFailure(String message);
}
public CheckLoginTask(String userName, String password, ResultListener listener) {
mUserName = userName;
mPassword = password;
mListener = listener;
}
#Override protected Boolean doInBackground(Void... voids) {
boolean isSuccess = false;
// do some process with username and password
// assume there is a a message
mMessage = "Invalid password";
return isSuccess;
}
#Override protected void onPostExecute(Boolean isSuccess) {
if(isSuccess) {
mListener.onSuccess(mMessage);
} else {
mListener.onFailure(mMessage);
}
}
}
that it can be used like this:
CheckLoginTask.ResultListener listener = new CheckLoginTask.ResultListener {
#Override
public void onSuccess(String message) {
// do something when success
}
#Override
public void onFailure(String message) {
// do something with failure
}
};
CheckLoginTask checkLoginTask = new CheckLoginTask(userName, password, listener);
checkLoginTask.execute();
For what i understand from your question, you want to check for
a password and then pass the result to the activity or somewhere else.
I suggest implementing interfaces to make your code simpler and more effective.
since AsyncTasks run on a different thread, they have methods to contact with the main thread such as onPreExecute() and onPostExecute(String r) , so what you have to do is the following :
create an interface that would look like something like that :
public interface PasswordChecker {
void onChecked(Boolean isSuccess);
}
the second thing is to make your activity or class implement this interface, it would be this way :
public class MyActivity extends AppCompatActivity implements PasswordChecker {
#Override
public void onChecked(Boolean isSuccess) {
if (isSuccess) {
//Do Stuff with your isSuccess Boolean
}
}
}
or you can initialize a PasswordChecker object variable and pass it as an argument in the third step.
Make your AsyncTask require a PasswordChecker and then you must pass your activity or class, or object as an argument to the constructor, your AsyncTask would look like this :
public class CheckLogin extends AsyncTask<String,String,Boolean> {
private PasswordChecker checker;
CheckLogin(PasswordChecker checker) {
this.checker = checker;
}
#Override
protected Boolean doInBackground(String... strings) {
boolean isSuccess;
//Do Your Work..
//...
//...
//if (condition)
isSuccess = true;
return isSuccess;
}
#Override
protected void onPostExecute(Boolean isSuccess) {
super.onPostExecute(isSuccess);
checker.onChecked(isSuccess);
}
}
Finally, you must initialize your AsyncTask using a PasswordChecker object as an argument :
//Passing the activity it self (which implements PasswordChecker) as an argument
final CheckLogin checkLogin = new CheckLogin(MyActivity.this);
or
//Or by passing a custom object
PasswordChecker myChecker = new PasswordChecker() {
#Override
public void onChecked(Boolean isSuccess) {
if (isSuccess) {
Toast.makeText(MyActivity.this , "Login Success!" , Toast.LENGTH_LONG).show();
}
else {
Toast.makeText(MyActivity.this , "Login Failed!" , Toast.LENGTH_LONG).show();
}
}
};
CheckLogin myCheckLogin = new CheckLogin(myChecker);
//Do the rest of the job
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//Execute your task
checkLogin.execute("Username", "Password");
}
});
Conclusion : As you can see here, the result is passed through onPostExecute(String r), your interface will be fired ( by checker.onChecked(isSuccess); ) every time onPostExecute is called, passing the boolean as an argument, and executes the code inside it depending on its value.
The problem is doInBackground() works an a different thread then your onClick(). onClick() works on the UIThread. so you don't recieve any updates to that thread.
First change your Async task declaration to this:
public class CheckLogin extends AsyncTask<Void, Void, Boolean>
The third parameter is the result parameter that is returned by doinbackground.
so your doInBackground() and onPostExecute()will be something like this:
#Override
protected Boolean doInBackground(Void... params) {
if(some_condition) {
return true;
} else {
return false;
}
}
#Override
protected void onPostExecute(Boolean result) {
// use the result
super.onPostExecute(result);
isSuccess = result;
};
I want to return a Boolean after a AsyncTask.
This is the AsyncTask (not the whole code because isn't important and sstackoverflow give me error):
public class CallSoap extends AsyncTask<CallSoapParams, Void, Void> {
public interface AsyncResponse {
void processFinish(String output);
}
private Context activityContext;
public AsyncResponse delegate = null;//Call back interface
public CallSoap(Context context, AsyncResponse asyncResponse) {
activityContext = context;
delegate = asyncResponse;
}
#Override
protected Void doInBackground(CallSoapParams... params) {
request = new SoapObject(params[0].NAMESPACE, params[0].METHOD_NAME);
// no important things
return null;
}
#Override
protected void onPostExecute(Void aVoid) {
super.onPostExecute(aVoid);
//dismiss ProgressDialog
delegate.processFinish(response.toString());
}
#Override
protected void onPreExecute() {
super.onPreExecute();
//create and show ProgressDialog
}
}
And this is the implementation on Activity (not the whole code because isn't important and sstackoverflow give me error):
private boolean checkDataRegistrationByServer() {
if (NickNameExist()) {
// DO STUFF
}
return true;
}
Boolean r;
private boolean NickNameExist() {
CallSoapParams callParams = new CallSoapParams(NICKNAME_EXIST);
CallSoap NickNameExistCall = new CallSoap(RegistrationActivity.this, new CallSoap.AsyncResponse() {
#Override
public void processFinish(String output) {
Log.d("Response From AsyTask:", output);
if (output.equals(FALSE_RESPONSE)) {
r = false;
Toast.makeText(getApplicationContext(), output + " - NickNameExistCall - Nick don't exist", Toast.LENGTH_SHORT).show();
} else {
r = true;
}
}
});
NickNameExistCall.execute(callParams);
return r;
}
I tried to create a global Boolean but the App crash. Someone can help me?
1) You don't have a response variable anywhere, and doInBackground has returned null instead of any response, so not clear how you got that value.
delegate.processFinish(response.toString());
2) You can't return from that function. And your app crashes probably because Boolean's can be null. boolean's cannot. However, you should not attempt to make a global variable here because that's not how asynchronous code should run.
What you need is to pass the callback through the function
private void checkDataRegistrationByServer(String data, CallSoap.AsyncResponse callback) {
CallSoap nickNameExistCall = new CallSoap(RegistrationActivity.this, callback);
CallSoapParams callParams = new CallSoapParams(data);
nickNameExistCall.execute(callParams);
}
Elsewhere...
final String nick = NICKNAME_EXIST;
checkDataRegistrationByServer(nick, new CallSoap.AsyncResponse() {
#Override
public void processFinish(String response) {
Log.d("Response From AsyncTask:", output);
boolean exists = !response.equals(FALSE_RESPONSE);
if (!exists) {
Toast.makeText(getApplicationContext(), output + " - NickNameExistCall - Nick " + nick + " doesn't exist", Toast.LENGTH_SHORT).show();
}
}
});
Note: If you make your AsyncTask just return a Boolean in the AsyncResponse you can shorten this code some.
I have this two classes. My main Activity and the one that extends the AsyncTask, Now in my main Activity I need to get the result from the OnPostExecute() in the AsyncTask. How can I pass or get the result to my main Activity?
Here is the sample codes.
My main Activity.
public class MainActivity extends Activity{
AasyncTask asyncTask = new AasyncTask();
#Override
public void onCreate(Bundle aBundle) {
super.onCreate(aBundle);
//Calling the AsyncTask class to start to execute.
asyncTask.execute(a.targetServer);
//Creating a TextView.
TextView displayUI = asyncTask.dataDisplay;
displayUI = new TextView(this);
this.setContentView(tTextView);
}
}
This is the AsyncTask class
public class AasyncTask extends AsyncTask<String, Void, String> {
TextView dataDisplay; //store the data
String soapAction = "http://sample.com"; //SOAPAction header line.
String targetServer = "https://sampletargeturl.com"; //Target Server.
//SOAP Request.
String soapRequest = "<sample XML request>";
#Override
protected String doInBackground(String... string) {
String responseStorage = null; //storage of the response
try {
//Uses URL and HttpURLConnection for server connection.
URL targetURL = new URL(targetServer);
HttpURLConnection httpCon = (HttpURLConnection) targetURL.openConnection();
httpCon.setDoOutput(true);
httpCon.setDoInput(true);
httpCon.setUseCaches(false);
httpCon.setChunkedStreamingMode(0);
//properties of SOAPAction header
httpCon.addRequestProperty("SOAPAction", soapAction);
httpCon.addRequestProperty("Content-Type", "text/xml; charset=utf-8");
httpCon.addRequestProperty("Content-Length", "" + soapRequest.length());
httpCon.setRequestMethod(HttpPost.METHOD_NAME);
//sending request to the server.
OutputStream outputStream = httpCon.getOutputStream();
Writer writer = new OutputStreamWriter(outputStream);
writer.write(soapRequest);
writer.flush();
writer.close();
//getting the response from the server
InputStream inputStream = httpCon.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
ByteArrayBuffer byteArrayBuffer = new ByteArrayBuffer(50);
int intResponse = httpCon.getResponseCode();
while ((intResponse = bufferedReader.read()) != -1) {
byteArrayBuffer.append(intResponse);
}
responseStorage = new String(byteArrayBuffer.toByteArray());
} catch (Exception aException) {
responseStorage = aException.getMessage();
}
return responseStorage;
}
protected void onPostExecute(String result) {
aTextView.setText(result);
}
}
Easy:
Create interface class, where String output is optional, or can be whatever variables you want to return.
public interface AsyncResponse {
void processFinish(String output);
}
Go to your AsyncTask class, and declare interface AsyncResponse as a field :
public class MyAsyncTask extends AsyncTask<Void, Void, String> {
public AsyncResponse delegate = null;
#Override
protected void onPostExecute(String result) {
delegate.processFinish(result);
}
}
In your main Activity you need to implements interface AsyncResponse.
public class MainActivity implements AsyncResponse{
MyAsyncTask asyncTask =new MyAsyncTask();
#Override
public void onCreate(Bundle savedInstanceState) {
//this to set delegate/listener back to this class
asyncTask.delegate = this;
//execute the async task
asyncTask.execute();
}
//this override the implemented method from asyncTask
#Override
void processFinish(String output){
//Here you will receive the result fired from async class
//of onPostExecute(result) method.
}
}
UPDATE
I didn't know this is such a favourite to many of you. So here's the simple and convenience way to use interface.
still using same interface. FYI, you may combine this into AsyncTask class.
in AsyncTask class :
public class MyAsyncTask extends AsyncTask<Void, Void, String> {
// you may separate this or combined to caller class.
public interface AsyncResponse {
void processFinish(String output);
}
public AsyncResponse delegate = null;
public MyAsyncTask(AsyncResponse delegate){
this.delegate = delegate;
}
#Override
protected void onPostExecute(String result) {
delegate.processFinish(result);
}
}
do this in your Activity class
public class MainActivity extends Activity {
MyAsyncTask asyncTask = new MyAsyncTask(new AsyncResponse(){
#Override
void processFinish(String output){
//Here you will receive the result fired from async class
//of onPostExecute(result) method.
}
}).execute();
}
Or, implementing the interface on the Activity again
public class MainActivity extends Activity
implements AsyncResponse{
#Override
public void onCreate(Bundle savedInstanceState) {
//execute the async task
new MyAsyncTask(this).execute();
}
//this override the implemented method from AsyncResponse
#Override
void processFinish(String output){
//Here you will receive the result fired from async class
//of onPostExecute(result) method.
}
}
As you can see 2 solutions above, the first and third one, it needs to create method processFinish, the other one, the method is inside the caller parameter. The third is more neat because there is no nested anonymous class.
Tip: Change String output, String response, and String result to different matching types in order to get different objects.
There are a few options:
Nest the AsyncTask class within your Activity class. Assuming you don't use the same task in multiple activities, this is the easiest way. All your code stays the same, you just move the existing task class to be a nested class inside your activity's class.
public class MyActivity extends Activity {
// existing Activity code
...
private class MyAsyncTask extends AsyncTask<String, Void, String> {
// existing AsyncTask code
...
}
}
Create a custom constructor for your AsyncTask that takes a reference to your Activity. You would instantiate the task with something like new MyAsyncTask(this).execute(param1, param2).
public class MyAsyncTask extends AsyncTask<String, Void, String> {
private Activity activity;
public MyAsyncTask(Activity activity) {
this.activity = activity;
}
// existing AsyncTask code
...
}
You can try this code in your Main class.
That worked for me, but i have implemented methods in other way
try {
String receivedData = new AsyncTask().execute("http://yourdomain.com/yourscript.php").get();
}
catch (ExecutionException | InterruptedException ei) {
ei.printStackTrace();
}
I felt the below approach is very easy.
I have declared an interface for callback
public interface AsyncResponse {
void processFinish(Object output);
}
Then created asynchronous Task for responding all type of parallel requests
public class MyAsyncTask extends AsyncTask<Object, Object, Object> {
public AsyncResponse delegate = null;//Call back interface
public MyAsyncTask(AsyncResponse asyncResponse) {
delegate = asyncResponse;//Assigning call back interfacethrough constructor
}
#Override
protected Object doInBackground(Object... params) {
//My Background tasks are written here
return {resutl Object}
}
#Override
protected void onPostExecute(Object result) {
delegate.processFinish(result);
}
}
Then Called the asynchronous task when clicking a button in activity Class.
public class MainActivity extends Activity{
#Override
public void onCreate(Bundle savedInstanceState) {
Button mbtnPress = (Button) findViewById(R.id.btnPress);
mbtnPress.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
MyAsyncTask asyncTask =new MyAsyncTask(new AsyncResponse() {
#Override
public void processFinish(Object output) {
Log.d("Response From Asynchronous task:", (String) output);
mbtnPress.setText((String) output);
}
});
asyncTask.execute(new Object[] { "Your request to aynchronous task class is giving here.." });
}
});
}
}
Thanks
This answer might be late but I would like to mention few things when your Activity dependent on AsyncTask. That would help you in prevent crashes and memory management. As already mentioned in above answers go with interface, we also say them callbacks. They will work as an informer, but never ever send strong reference of Activity or interface always use weak reference in those cases.
Please refer to below screenshot to findout how that can cause issues.
As you can see if we started AsyncTask with a strong reference then there is no guarantee that our Activity/Fragment will be alive till we get data, so it would be better to use WeakReference in those cases and that will also help in memory management as we will never hold the strong reference of our Activity then it will be eligible for garbage collection after its distortion.
Check below code snippet to find out how to use awesome WeakReference -
MyTaskInformer.java Interface which will work as an informer.
public interface MyTaskInformer {
void onTaskDone(String output);
}
MySmallAsyncTask.java AsyncTask to do long running task, which will use WeakReference.
public class MySmallAsyncTask extends AsyncTask<String, Void, String> {
// ***** Hold weak reference *****
private WeakReference<MyTaskInformer> mCallBack;
public MySmallAsyncTask(MyTaskInformer callback) {
this.mCallBack = new WeakReference<>(callback);
}
#Override
protected String doInBackground(String... params) {
// Here do whatever your task is like reading/writing file
// or read data from your server or any other heavy task
// Let us suppose here you get response, just return it
final String output = "Any out, mine is just demo output";
// Return it from here to post execute
return output;
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
// Here you can't guarantee that Activity/Fragment is alive who started this AsyncTask
// Make sure your caller is active
final MyTaskInformer callBack = mCallBack.get();
if(callBack != null) {
callBack.onTaskDone(s);
}
}
}
MainActivity.java This class is used to start my AsyncTask implement interface on this class and override this mandatory method.
public class MainActivity extends Activity implements MyTaskInformer {
private TextView mMyTextView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mMyTextView = (TextView) findViewById(R.id.tv_text_view);
// Start your AsyncTask and pass reference of MyTaskInformer in constructor
new MySmallAsyncTask(this).execute();
}
#Override
public void onTaskDone(String output) {
// Here you will receive output only if your Activity is alive.
// no need to add checks like if(!isFinishing())
mMyTextView.setText(output);
}
}
You can do it in a few lines, just override onPostExecute when you call your AsyncTask. Here is an example for you:
new AasyncTask()
{
#Override public void onPostExecute(String result)
{
// do whatever you want with result
}
}.execute(a.targetServer);
I hope it helped you, happy codding :)
in your Oncreate():
`
myTask.execute("url");
String result = "";
try {
result = myTask.get().toString();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}`
Why do people make it so hard.
This should be sufficient.
Do not implement the onPostExecute on the async task, rather implement it on the Activity:
public class MainActivity extends Activity
{
#Override
public void onCreate(Bundle savedInstanceState) {
//execute the async task
MyAsyncTask task = new MyAsyncTask(){
protected void onPostExecute(String result) {
//Do your thing
}
}
task.execute("Param");
}
}
You can call the get() method of AsyncTask (or the overloaded get(long, TimeUnit)). This method will block until the AsyncTask has completed its work, at which point it will return you the Result.
It would be wise to be doing other work between the creation/start of your async task and calling the get method, otherwise you aren't utilizing the async task very efficiently.
You can write your own listener. It's same as HelmiB's answer but looks more natural:
Create listener interface:
public interface myAsyncTaskCompletedListener {
void onMyAsynTaskCompleted(int responseCode, String result);
}
Then write your asynchronous task:
public class myAsyncTask extends AsyncTask<String, Void, String> {
private myAsyncTaskCompletedListener listener;
private int responseCode = 0;
public myAsyncTask() {
}
public myAsyncTask(myAsyncTaskCompletedListener listener, int responseCode) {
this.listener = listener;
this.responseCode = responseCode;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected String doInBackground(String... params) {
String result;
String param = (params.length == 0) ? null : params[0];
if (param != null) {
// Do some background jobs, like httprequest...
return result;
}
return null;
}
#Override
protected void onPostExecute(String finalResult) {
super.onPostExecute(finalResult);
if (!isCancelled()) {
if (listener != null) {
listener.onMyAsynTaskCompleted(responseCode, finalResult);
}
}
}
}
Finally implement listener in activity:
public class MainActivity extends AppCompatActivity implements myAsyncTaskCompletedListener {
#Override
public void onMyAsynTaskCompleted(int responseCode, String result) {
switch (responseCode) {
case TASK_CODE_ONE:
// Do something for CODE_ONE
break;
case TASK_CODE_TWO:
// Do something for CODE_TWO
break;
default:
// Show some error code
}
}
And this is how you can call asyncTask:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Some other codes...
new myAsyncTask(this,TASK_CODE_ONE).execute("Data for background job");
// And some another codes...
}
Hi you can make something like this:
Create class which implements AsyncTask
// TASK
public class SomeClass extends AsyncTask<Void, Void, String>>
{
private OnTaskExecutionFinished _task_finished_event;
public interface OnTaskExecutionFinished
{
public void OnTaskFihishedEvent(String Reslut);
}
public void setOnTaskFinishedEvent(OnTaskExecutionFinished _event)
{
if(_event != null)
{
this._task_finished_event = _event;
}
}
#Override
protected void onPreExecute()
{
super.onPreExecute();
}
#Override
protected String doInBackground(Void... params)
{
// do your background task here ...
return "Done!";
}
#Override
protected void onPostExecute(String result)
{
super.onPostExecute(result);
if(this._task_finished_event != null)
{
this._task_finished_event.OnTaskFihishedEvent(result);
}
else
{
Log.d("SomeClass", "task_finished even is null");
}
}
}
Add in Main Activity
// MAIN ACTIVITY
public class MyActivity extends ListActivity
{
...
SomeClass _some_class = new SomeClass();
_someclass.setOnTaskFinishedEvent(new _some_class.OnTaskExecutionFinished()
{
#Override
public void OnTaskFihishedEvent(String result)
{
Toast.makeText(getApplicationContext(),
"Phony thread finished: " + result,
Toast.LENGTH_SHORT).show();
}
});
_some_class.execute();
...
}
Create a static member in your Activity class. Then assign the value during the onPostExecute
For example, if the result of your AsyncTask is a String, create a public static string in your Activity
public static String dataFromAsyncTask;
Then, in the onPostExecute of the AsyncTask, simply make a static call to your main class and set the value.
MainActivity.dataFromAsyncTask = "result blah";
I make it work by using threading and handler/message.
Steps as follow:
Declare a progress Dialog
ProgressDialog loadingdialog;
Create a function to close dialog when operation is finished.
private Handler handler = new Handler() {
#Override
public void handleMessage(Message msg) {
loadingdialog.dismiss();
}
};
Code your Execution details:
public void startUpload(String filepath) {
loadingdialog = ProgressDialog.show(MainActivity.this, "Uploading", "Uploading Please Wait", true);
final String _path = filepath;
new Thread() {
public void run() {
try {
UploadFile(_path, getHostName(), getPortNo());
handler.sendEmptyMessage(0);
} catch (Exception e) {
Log.e("threadmessage", e.getMessage());
}
}
}.start();
}
You need to use "protocols" to delegate or provide data to the AsynTask.
Delegates and Data Sources
A delegate is an object that acts on behalf of, or in coordination with, another object when that object encounters an event in a program. (Apple definition)
protocols are interfaces that define some methods to delegate some behaviors.
Here is a complete example!!!
try this:
public class SomAsyncTask extends AsyncTask<String, Integer, JSONObject> {
private CallBack callBack;
public interface CallBack {
void async( JSONObject jsonResult );
void sync( JSONObject jsonResult );
void progress( Integer... status );
void cancel();
}
public SomAsyncTask(CallBack callBack) {
this.callBack = callBack;
}
#Override
protected JSONObject doInBackground(String... strings) {
JSONObject dataJson = null;
//TODO query, get some dataJson
if(this.callBack != null)
this.callBack.async( dataJson );// asynchronize with MAIN LOOP THREAD
return dataJson;
}
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
if(this.callBack != null)
this.callBack.progress(values);// synchronize with MAIN LOOP THREAD
}
#Override
protected void onPostExecute(JSONObject jsonObject) {
super.onPostExecute(jsonObject);
if(this.callBack != null)
this.callBack.sync(jsonObject);// synchronize with MAIN LOOP THREAD
}
#Override
protected void onCancelled() {
super.onCancelled();
if(this.callBack != null)
this.callBack.cancel();
}
}
And usage example:
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final Context _localContext = getContext();
SomeAsyncTask.CallBack someCallBack = new SomeAsyncTask.CallBack() {
#Override
public void async(JSONObject jsonResult) {//async thread
//some async process, e.g. send data to server...
}
#Override
public void sync(JSONObject jsonResult) {//sync thread
//get result...
//get some resource of Activity variable...
Resources resources = _localContext.getResources();
}
#Override
public void progress(Integer... status) {//sync thread
//e.g. change status progress bar...
}
#Override
public void cancel() {
}
};
new SomeAsyncTask( someCallBack )
.execute("someParams0", "someParams1", "someParams2");
}
Probably going overboard a bit but i provided call backs for both the execution code and the results. obviously for thread safety you want to be careful what you access in your execution callback.
The AsyncTask implementation:
public class AsyncDbCall<ExecuteType,ResultType> extends AsyncTask<ExecuteType, Void,
ResultType>
{
public interface ExecuteCallback<E, R>
{
public R execute(E executeInput);
}
public interface PostExecuteCallback<R>
{
public void finish(R result);
}
private PostExecuteCallback<ResultType> _resultCallback = null;
private ExecuteCallback<ExecuteType,ResultType> _executeCallback = null;
AsyncDbCall(ExecuteCallback<ExecuteType,ResultType> executeCallback, PostExecuteCallback<ResultType> postExecuteCallback)
{
_resultCallback = postExecuteCallback;
_executeCallback = executeCallback;
}
AsyncDbCall(ExecuteCallback<ExecuteType,ResultType> executeCallback)
{
_executeCallback = executeCallback;
}
#Override
protected ResultType doInBackground(final ExecuteType... params)
{
return _executeCallback.execute(params[0]);
}
#Override
protected void onPostExecute(ResultType result)
{
if(_resultCallback != null)
_resultCallback.finish(result);
}
}
A callback:
AsyncDbCall.ExecuteCallback<Device, Device> updateDeviceCallback = new
AsyncDbCall.ExecuteCallback<Device, Device>()
{
#Override
public Device execute(Device device)
{
deviceDao.updateDevice(device);
return device;
}
};
And finally execution of the async task:
new AsyncDbCall<>(addDeviceCallback, resultCallback).execute(device);
Hope you been through this , if not please read.
https://developer.android.com/reference/android/os/AsyncTask
Depending on the nature of result data, you should choose best possible option you can think of.
It is a great choice to use an Interface
some other options would be..
If the AsyncTask class is defined inside the very class you want to
use the result in.Use a static global variable or get() , use it from
outer class (volatile variable if necessary). but should be aware of the AsyncTask progress or should at least make sure that it have finished the task and result is
available through global variable / get() method. you may use
polling, onProgressUpdate(Progress...), synchronization or interfaces (Which ever suits best for you)
If the Result is compatible to be a sharedPreference entry or it is okay to be saved as a file in the memory you could save it even from
the background task itself and could use the onPostExecute() method
to get notified when the result is available in the memory.
If the string is small enough, and is to be used with start of an
activity. it is possible to use intents (putExtra()) within
onPostExecute() , but remember that static contexts aren't that safe
to deal with.
If possible, you can call a static method from the
onPostExecute() method, with the result being your parameter
FOllowing is my piece of code:
class GraphicsView extends GLSurfaceView
{
public void LoadProjectFile(String Filename)
{
m_Renderer.m_Project=new Project();
m_Renderer.m_SelectedProjectPath = Filename;
try {
m_Renderer.m_Project.load_file(Filename);
}
catch (Exception e)
{
throw new MalformedURLException();
}
}}
public class Map extends Activity
{
private GraphicsView mGLView;
//private GisGLRenderer m_GisRenderer;
final static String RESULT_KEY="result";
final static int REQ_CODE=1001;
AlertDialog m=null;
public class LoadFile extends AsyncTask<String,String,String>
{
ProgressDialog Asycdialog = new ProgressDialog(Map.this);
#Override
protected void onPreExecute() {
//set message of the dialog
super.onPreExecute();
Asycdialog.setMessage("Loading File");
Asycdialog.setButton(DialogInterface.BUTTON_NEGATIVE,"Cancel",new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialogInterface, int i) {
}
});
//show dialog
if (!Map.this.isFinishing())
{
Asycdialog.show();
}
}
protected void onProgressUpdate(String ... progress)
{
}
protected String doInBackground(String ... Params)
{
try{
Map.this.mGLView.LoadProjectFile(AppFuncs.g_path);
}
catch (Exception e)
{
Toast.makeText(Map.this,"Project file missing please upload project file ",Toast.LENGTH_SHORT).show();
}
Map.this.mGLView.requestRender();
return null;
}
protected void onPostExecute(String result)
{
Asycdialog.dismiss();
super.onPostExecute(result);
}
}
}
I am calling loadProjectfile function from MAP class. i want to handle exception that comes in loadprojectfile in Map class. But i am getting error exception is not reported.
If you want to handle it in Map class then throw Exception from LoadProjectFile method and also remove the try..catch block.
public void LoadProjectFile(String Filename) throws Exception
{
m_Renderer.m_Project=new Project();
m_Renderer.m_SelectedProjectPath = Filename;
m_Renderer.m_Project.load_file(Filename);
}
Modify this
public void LoadProjectFile(String Filename)
to this:
public void LoadProjectFile(String Filename) throws Exception
and remove try-catch from the method