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How do i return a result from a async task [duplicate]

This question already has answers here:
How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class?
(17 answers)
Closed 7 years ago.
I have been using async tasks to hit a web server and updating controls using the result. This has drawbacks, namely it makes the async methods specific to controls and stops me using the returned string again.
How do i return the resulting string from a async call onPostExecute? How do i call it? I cant seem to get my code able to do that. There should be no issues with threading as i have a dialog that freezes the UI until job is done.
My typical asyncTask code is as follows
class GetDataFromServer extends AsyncTask<String, String, String>
{
* */
// Progress Dialog
private ProgressDialog qDialog;
private Context context;
private String dialogString;
private ArrayList<String[]> newLoginResult;
// JSON parser class
String url_newGame ="http://xxxxxx.php";
public myAsyncMethos(String dialogMessage, Context con)
{
this.qDialog = new ProgressDialog(con);
this.dialogString = dialogMessage;
this.context = con;
}
/**
* Before starting background thread Show Progress Dialog
* */
#Override
protected void onPreExecute()
{
super.onPreExecute();
qDialog = new ProgressDialog(this.context);
qDialog.setMessage(this.dialogString);
qDialog.setIndeterminate(false);
qDialog.setCancelable(false);
qDialog.show();
}
#Override
protected JSONObject doInBackground(String... args)
{
//MAKE SERVER CALL and cast to JSONOBject
return jsonNewUser;
}
public void onPostExecute(JSONObject jsonString)
{
// dismiss the dialog after getting response
qDialog.dismiss();
//I WANT TO RETURN A STRING HERE BUT KEEP GETTING SYNTAX ERRORS BEFORE RUNTIME
}
}

I would personally add a callback to your class, then once onPostExecute is run, fire off your callback to the listener on the main class.
class GetDataFromServer extends AsyncTask<String, String,JSONObject>
{
// Progress Dialog
private ProgressDialog qDialog;
private Context context;
private String dialogString;
private ArrayList<String[]> newLoginResult;
private InformComplete myCallback;
public GetDataFromServer(String dialogMessage, Context con,InformComplete callback)
{
this.qDialog = new ProgressDialog(con);
this.dialogString = dialogMessage;
this.context = con;
this.myCallback=callback;
}
#Override
protected void onPreExecute()
{
// set up your dialog
}
#Override
protected JSONObject doInBackground(String... args)
{
JSONObject jsonNewUser=new JSONObject();
return jsonNewUser;
}
public void onPostExecute(JSONObject jsonString)
{
qDialog.dismiss();
myCallback.PostData(jsonString);
}
public interface InformComplete
{
public void PostData(JSONObject result);
}
}
Then from your calling class, you'd have something like this...
private void callTheAsyncThing
{
GetDataFromServer gds=new GetDataFromServer("please wait", this, letMeKnow);
gds.execute(params);
}
private InformComplete letMeKnow=new InformComplete()
{
public void PostData(JSONObject result)
{
// we now have the data in the calling class
}
};

You can't return a value in methods from AsynTask cause it used to return a void element. So, you can instance global var foe example, and set the value to it. Like...
`
class GetDataFromServer extends AsyncTask<String, String, String>
{
* */
// Progress Dialog
private ProgressDialog qDialog;
private Context context;
private String dialogString;
private ArrayList<String[]> newLoginResult;
private String value;
// JSON parser class
String url_newGame ="http://xxxxxx.php";
public myAsyncMethos(String dialogMessage, Context con)
{
this.qDialog = new ProgressDialog(con);
this.dialogString = dialogMessage;
this.context = con;
}
/**
* Before starting background thread Show Progress Dialog
* */
#Override
protected void onPreExecute()
{
super.onPreExecute();
qDialog = new ProgressDialog(this.context);
qDialog.setMessage(this.dialogString);
qDialog.setIndeterminate(false);
qDialog.setCancelable(false);
qDialog.show();
}
#Override
protected JSONObject doInBackground(String... args)
{
//MAKE SERVER CALL and cast to JSONOBject
return jsonNewUser;
}
public void onPostExecute(JSONObject jsonString)
{
// dismiss the dialog after getting response
qDialog.dismiss();
value = "Whatever you want";
}
public void setValue(String value){
this.value=value;
}
public String getValue(){
return this.value;
}
}`
And then use it. There is one way to return something. Btw you can't change return.

the method of onPostExecute is not Programmer call,it called by AsyncTask instance.if you want to return a result from a async task,you can send a parameter into GetDataFromServer ,and in method of onPostExecute,you give him the new value，and then,you can use Handler to send a message.

Your return JSONObject in doInBackground method while you try to get string in onPostExecute method.
public void onPostExecute(JsonObject jsonString)
{
// dismiss the dialog after getting response
qDialog.dismiss();
//I WANT TO RETURN A STRING HERE BUT KEEP GETTING SYNTAX ERRORS BEFORE RUNTIME
}

ProgressDialog in AsyncTask called from DialogFragment is not shown

I am executing an AsyncTask from inside a DialogFragment but the progress bar is not shown during doInBackground. Here is the code:
public class GetCustomerSoapAsync extends AsyncTask<Void, Void, String>
{
ProgressDialog prg;
ActionBarActivity activity;
GetResponseFromGetCustomer listener;
public GetCustomerSoapAsync(ActionBarActivity activity, GetResponseFromGetCustomer listener)
{
this.activity = activity;
this.listener = listener;
prg = new ProgressDialog(activity);
prg.setMessage("Lütfen Bekleyin");
Log.i("ED","Progress will be shown");
prg.show();
}
#Override protected String doInBackground(Void... params)
{
//some stuff
}
#Override protected void onPostExecute(String s)
{
listener.getResponseFromGetCustomer(s);
if (prg.isShowing())
{
prg.dismiss();
}
}
and where I call it:
public class B1_PhoneNumberFragment extends android.support.v4.app.Fragment
{
...
buttonLogin.setOnClickListener(new OnClickListener()
{
#Override
public void onClick(View v)
{
...
PhoneNumberVerified dialog = new PhoneNumberVerified();
dialog.show(getFragmentManager(), "NumberVerifiedByUser");
}
...
}
....
public class PhoneNumberVerified extends DialogFragment
{
#Override
public Dialog onCreateDialog(Bundle savedInstanceState)
{
// Use the Builder class for convenient dialog construction
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
// Format of this dialog will be changed
builder.setMessage("Numaranız doğru mu?\n" + "0" + number)
.setPositiveButton(R.string.yes,
new DialogInterface.OnClickListener()
{
public void onClick(DialogInterface dialog,
int id)
{
GlobalApplication.getUser().setPhone(
(excludeParanthesis
(number)));
//AsyncTask is not working properly,
// progress dialog is not shown and code flows before
// response is set to s
GetCustomerSoapAsync getCustomerSoapAsync =
new GetCustomerSoapAsync(
(ActionBarActivity) getActivity(),
new GetResponseFromGetCustomer()
{
#Override
public void getResponseFromGetCustomer
(String s)
{
response = s;
}
});
getCustomerSoapAsync.execute();
Log.i("ED", "Response after GetCustomerSoapAsync callback: " +
response);
}
And finally, maybe because of the flawed flow of the tasks or maybe something else, the callback can't do its job, and response is not set to return value of the AsyncTask.
Thanks for any help!

You should use onPreExecute :
class Task1 extends AsyncTask<Object, Void, String []> {
/** The Progress dialog. */
private final ProgressDialog dialog = new ProgressDialog(YourActivity.this);
/**
* Set the Progress dialog.
*/
protected void onPreExecute()
{
super.onPreExecute();
this.dialog.setMessage("Loading...");
this.dialog.show();
dialog.setCanceledOnTouchOutside(false);
}
protected String[] doInBackground(Object... params) {
///
}
protected void onPostExecute(String [] result)
{
super.onPostExecute(result);
this.dialog.dismiss();
}
}
To call it you should:
Task1 myTask = new Task1();
myTask.execute(stopArrey, start, end);
Hope it helped! :)

You need to operate on the ProgressDialog only on the UI Thread.
The constructor on the asynctask gives great flexibility enough to put the task in it's own class. Note: It's important that any field that is initialized in the Constructor on your custom AsyncTask takes advantage of the java final keyword so the field variables get automatic null for garbage collection.
Solution ProgressDialog code needs to be invoked in onPreExecute() where the task is still on the UI thread.
public class GetCustomerSoapAsync extends AsyncTask<Void, Void, String>
{
ProgressDialog prg;
// use final for fields initialized in a constructor.
final ActionBarActivity activity;
final GetResponseFromGetCustomer listener;
//The example below passes in the ProgressDialog from the caller where it's already shown. Pass it in to have access in the async tasks publish Progress method. Dismiss the ProgressDialog in the listener method; You didn't show your listener so this is just a technique
public GetCustomerSoapAsync(ActionBarActivity activity, GetResponseFromGetCustomer listener, ProgressDialog prg)
{
this.activity = activity;
this.listener = listener;
this.prg = prg;
// or move this code to onPreExecute() where it runs on the UI thread.
// move this code to onPreExecute()
//prg = new ProgressDialog(activity);
//prg.setMessage("Lütfen Bekleyin");
//Log.i("ED","Progress will be shown");
//prg.show();
}

Ok the issue I believe is you have to declare the PD in the layout visible to the user before the Aysnch task is executing.
For example:
//Declare the pd here. Pd private to class.
private ProgressDialog pd;
builder.setMessage("Numaranız doğru mu?\n" + "0" + number)
.setPositiveButton(R.string.yes,
new DialogInterface.OnClickListener()
{
....
pd = ProgressDialog.show(getActivity(), "",
"Your Message Here!!!", false);
// Now using a modified constructor call your execute function
//Previous parametes + pd
GetCustomerSoapAsync gCSA = new GetCustomerSoapAsync(...,...,pd);
getCustomerSoapAsync.execute();
}
Then in your Asynch class:
public class GetCustomerSoapAsync extends AsyncTask<Void, Void, String>
{
ProgressDialog prg;
ActionBarActivity activity;
GetResponseFromGetCustomer listener;
public GetCustomerSoapAsync(ActionBarActivity activity, GetResponseFromGetCustomer listener,ProgressDialog pd)
ProgressDialog prg;
{
this.activity = activity;
this.listener = listener;
this.prg = pd;
}
#Override protected String doInBackground(Void... params)
{
//some stuff
}
#Override protected void onPostExecute(String s)
{
listener.getResponseFromGetCustomer(s);
if (prg.isShowing())
{
prg.dismiss();
}
}
Ps: I don't know if you are using fragments as a implementation but if you are you must refer to the same pd you called in the onclick function in the fragment via rootview else you might be calling functions on a progresss dialog that never showed in the first place.

Android display a ProgressDialog on a ListActivity when using multiple external AsynTasks

So I am completely new to Andorid programming and can't seem to get a ProgressDialog to show on a ListActivity (ScheduleActiviy in my example) when running an AsyncTask from a separate class (GetGames in my example). I am attempting to use separate class for code re-usability. When I previously had the AsyncTask as an embedded class it seemed to work. I have posted what I believe to be all the relevant code. Any help would be great. Thanks!
ScheduleActivity.java
public class ScheduleActivity extends ListActivity
{
private final String PDIALOG_MSG = "Loading schedule...";
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.schedule);
ArrayList<HashMap<String, String>> gamesList = null;
try
{
// Loading information in Background Threads
gamesList = new GetGames(ScheduleActivity.this, PDIALOG_MSG).execute().get();
GetGames.java
public class GetGames extends AsyncTask<Void, Void, ArrayList<HashMap<String, String>>>
{
private Context context;
private ProgressDialog pDialog;
private String pDialogMsg;
public GetGames(Context ctx, String dialogMsg)
{
context = ctx;
pDialogMsg = dialogMsg;
}
#Override
public void onPreExecute()
{
super.onPreExecute();
pDialog = new ProgressDialog(context);
pDialog.setMessage(pDialogMsg);
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
#Override
public void onPostExecute(ArrayList<HashMap<String, String>> rtnList)
{
pDialog.dismiss();
}

Your ProgressDialog should probably be controlled on the Activity level instead of the AsyncTask level. Theoretically I don't see why how you're doing it wouldn't work, but I can show you a method which definitely works (it's what I do) and it organizes things a bit differently:
//In AsyncTask
#Override
protected void onPreExecute() {
showProgressDialog(R.string.importing_pages);
}
#Override
public void onPostExecute(Boolean b) {
hideProgressDialog();
}
//In Activity
public void showProgressDialog(int msgResId) {
showProgressDialog(getString(msgResId));
}
public void showProgressDialog(String msg) {
mProgressDialog = ProgressDialogHelper.buildDialog(this, msg);
mProgressDialog.show();
}
public void hideProgressDialog() {
if(mProgressDialog != null)
mProgressDialog.dismiss();
}
//My progress dialog helper class:
public class ProgressDialogHelper {
/**
* Creates a generic progress dialog with the specified message
*
* #param activity the activity which hosts the dialog. This must be an activity, not a context.
* #param msgResId the resId for the message to display
* #return a progress dialog
*/
public static ProgressDialog buildDialog(Activity activity, int msgResId) {
return buildDialog(activity, activity.getApplicationContext().getString(msgResId));
}
/**
* Creates a generic progress dialog with the specified message
*
* #param activity the activity which hosts the dialog. This must be an activity, not a context.
* #param msg the message to display
* #return a progress dialog
*/
public static ProgressDialog buildDialog(Activity activity, String msg) {
ProgressDialog dialog;
if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
dialog = new ProgressDialog(new ContextThemeWrapper(activity, android.R.style.Theme_Holo_Dialog));
else
dialog = new ProgressDialog(activity);
dialog.setMessage(msg);
dialog.setCancelable(false);
return dialog;
}
}
You don't have to make a helper class if you don't want to, it's just how I organized it. The main idea here is that the progress dialog should be owned by the Activity instead of the AsyncTask.
Also, the context used must be the activity's, not getApplicationContext(). It looks like you have that part right though.

You can display Progress Dialogs using AsyncTasks. That's not a problem. I do it all the time. What may be the problem is the doInBackground() method. What do you have there?
I also generally nest the AsyncTasks within the Activity class, so that it can call other Activity class methods in the onPostExecute() method. Otherwise, in order for it to communicate back with your Activity you'll have to use something like a handler or static references.
public class TestActivity extends Activity {
private AsyncTask<Void, Void, ArrayList<String>> bgLoader;
private ArrayList<String> listOfStuff;
private TextView textView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity);
listOfStuff = new ArrayList<String>();
textView = (TextView) findViewById(R.id.textView);
textView.setText("Your list has " + listOfStuff.size() + " items in it!");
bgLoader = new MyAsyncTask(this, "Waiting...").execute();
}
private void resumeDoingStuff() {
try {
listOfStuff = bgLoader.get();
textView.setText("Your list has " + listOfStuff.size() + " items in it!");
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
public class MyAsyncTask extends AsyncTask<Void, Void, ArrayList<String>> {
private ProgressDialog progressDialog;
private String message;
private Context ctx;
public MyAsyncTask(Context context, String message) {
this.ctx = context;
this.message = message;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
progressDialog = new ProgressDialog(ctx);
progressDialog.setMessage(message);
progressDialog.setIndeterminate(false);
progressDialog.setCancelable(false);
progressDialog.show();
}
#Override
protected ArrayList<String> doInBackground(Void... params) {
ArrayList<String> retList = new ArrayList<String>();
for (int i = 0; i < 10; i++) {
try {
retList.add("TEST STRING " + i);
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return retList;
}
#Override
protected void onPostExecute(ArrayList<String> result) {
progressDialog.dismiss();
resumeDoingStuff();
}
}
}

Android: How to update an UI from AsyncTask if AsyncTask is in a separate class?

I hate inner class.
I've a main activity who launches a 'short-life' AsyncTask.
AsyncTask is in a separate file, is not an inner class of main activity
I need async task updates a textView from main Activity.
I know i can update a TextView from onProgressUpdate, if AsyncTask is a inner class
But how from an external, indipendent, async task ?
UPDATE: This looks like working :
In acitivty i call the task
backgroundTask = new BackgroundTask(this);
backgroundTask.execute();
In the constructor i've
public BackgroundTask(Activity myContext)
{
debug = (TextView) myContext.findViewById(R.id.debugText);
}
where debug was a private field of AsyncTask.
So onProgressUpdate I can
debug.append(text);
Thanks for all of you suggestions

AsyncTask is always separate class from Activity, but I suspect you mean it is in different file than your activity class file, so you cannot benefit from being activity's inner class. Simply pass Activity context as argument to your Async Task (i.e. to its constructor)
class MyAsyncTask extends AsyncTask<URL, Integer, Long> {
WeakReference<Activity> mWeakActivity;
public MyAsyncTask(Activity activity) {
mWeakActivity = new WeakReference<Activity>(activity);
}
...
and use when you need it (remember to NOT use in during doInBackground()) i.e. so when you would normally call
int id = findViewById(...)
in AsyncTask you call i.e.
Activity activity = mWeakActivity.get();
if (activity != null) {
int id = activity.findViewById(...);
}
Note that our Activity can be gone while doInBackground() is in progress (so the reference returned can become null), but by using WeakReference we do not prevent GC from collecting it (and leaking memory) and as Activity is gone, it's usually pointless to even try to update it state (still, depending on your logic you may want to do something like changing internal state or update DB, but touching UI must be skipped).

Using Interface
1) Create one Interface
public interface OnDataSendToActivity {
public void sendData(String str);
}
2) Implements it in your Activity
public class MainActivity extends Activity implements OnDataSendToActivity{
#Override
protected void onCreate(Bundle savedInstanceState) {
new AsyncTest(this).execute(new String[]{"AnyData"}); // start your task
}
#Override
public void sendData(String str) {
// TODO Auto-generated method stub
}
}
3) Create constructor in AsyncTask(Activity activity){}
Register your Interface in AsyncTask file
and call interface method as below.
public class AsyncTest extends AsyncTask<String, Integer, String> {
OnDataSendToActivity dataSendToActivity;
public AsyncTest(Activity activity){
dataSendToActivity = (OnDataSendToActivity)activity;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
dataSendToActivity.sendData(result);
}
}
Here, your OnPostExecute will call after all task done by AsyncTask and will get "result"
as a parameter, returned by doInBackground(){ return "";}.
While "dataSendToActivity.sendData(result);" it will call activity's overrided method "public void sendData(String str) {}".
An edge case to remember: Be sure to pass this, i.e. you current activity's context to AsyncTask and not create another instance of your activity, otherwise your Activity will be destroyed and new one is created.

Make an static function in your activity class passing context in it to update your text view and then call this function in your AsynkTask class to update.
In Activity class:
public static void updateTextView(){
//your code here
}
In AynckTask class call this function.

Just pass the context (activity or whatever) to your AsyncTask in a constructor and then in onSuccess or onProgressUpdate call whatever you need on the context.

I wrote a small extension to AsyncTask for this kind of scenario. It allows you to keep your AsyncTask in a separate class, but also gives you convenient access to the Tasks's completion:
public abstract class ListenableAsyncTask<Params, Progress, Result> extends AsyncTask<Params, Progress, Result>{
#Override
protected final void onPostExecute(Result result) {
notifyListenerOnPostExecute(result);
}
private AsyncTaskListener<Result> mListener;
public interface AsyncTaskListener<Result>{
public void onPostExecute(Result result);
}
public void listenWith(AsyncTaskListener<Result> l){
mListener = l;
}
private void notifyListenerOnPostExecute(Result result){
if(mListener != null)
mListener.onPostExecute(result);
}
}
So first you extend ListenableAsyncTask instead of AsyncTask. Then in your UI code, make a concrete instance and set listenWith(...).

The Question has already been answered, still im posting how it should be done i guess..
Mainactivity class
public class MainActivity extends Activity implements OnClickListener
{
TextView Ctemp;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Ctemp = (TextView) findViewById(R.id.Ctemp);
doConv = (Button) findViewById(R.id.doConv);
doConv.setOnClickListener(this);
}
#Override
public void onClick(View arg0) // The conversion to do
{
new asyncConvert(this).execute();
}
}
now in the async class
public class asyncConvert extends AsyncTask<Void, Void, String>
{
SoapPrimitive response = null;
Context context;
public asyncConvert(Context callerclass)
{
contextGUI = callerclass;
}
.
.
.
.
protected void onPostExecute(String result)
{
((MainActivity) contextGUI).Ctemp.setText(result); // changing TextView
}
}

/**
* Background Async Task to Load all product by making HTTP Request
* */
public static class updateTExtviewAsyncTask extends AsyncTask<String, String, String> {
Context context;
ProgressDialog pDialog;
String id, name;
String state_id;
//--- Constructor for getting network id from asking method
public updateTExtviewAsyncTask(Context context,String id,String city)
{
context = context;
state_id = id;
city_name = city;
}
/* *
* Before starting background thread Show Progress Dialog
* */
#Override
protected void onPreExecute()
{
super.onPreExecute();
pDialog = ProgressDialog.show(context, "","Please wait...", true, true);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args)
{
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
YourClass.UpdateTextViewData("Textview data");
}
}
// place this code inside your activity class and also declare updating textview static
public static void UpdateTextViewData(String tvData)
{
tv.setText(tvData);
}

ProgressDialog is not shown in the AsyncTask

Document doc = new Obtainer(context, uri).execute().get();
This code in the activity class renders the Obtainer(which extends AsyncTask) which gets the xml document from the url. This is the onPreExecute method:
protected void onPreExecute() {
super.onPreExecute();
System.out.println("Pre execute began");
exception = null;
dialog = new ProgressDialog(context);
dialog.setMessage("Loading started");
dialog.setIndeterminate(true);
dialog.setCancelable(false);
System.out.println("Preexecute end");
dialog.show();
}
context is set in the Constructor:
public Obtainer(Context c, String addr) {
context = c;
address = addr;
}
During the runtime I can see in the console output both "Pre execute began" and "Preexecute end" but the progress dialog is not shown. What is the probleM?

Use this code, it works for me:
class Obtainer extends AsyncTask<Void, Void, Void> {
private ProgressDialog dialog;
#Override
protected void onPreExecute() {
dialog = new ProgressDialog(App.this); // App - your main activity class
dialog.setMessage("Please, wait...");
dialog.show();
}
#Override
protected Void doInBackground(Void... params) {
// ...
}
#Override
protected void onPostExecute(Void result) {
dialog.dismiss();
}
}
And in your main activity class method call
new Obtainer().execute();

What Context are you passing when you create your Obtainer (AsyncTask subclass)?
If you are using the Application context via getApplicationContext(), it can not be used to create a Dialog (or any View for that matter). You need to pass it a Context that can create Views.
"If you're in the habit of using your application context (from a call to getApplicationContext(), for example) in places where you need a Context to create views, it's only a matter of time until you find a case where things don't work quite like you would want or expect."
From: https://plus.google.com/107708120842840792570/posts/VTeRBsAeyTi