Android: Cancel Async Task

Android: Cancel Async Task

FOUND THE SOLUTION:
I added an action listener before uploadingDialog.show() like this:

    uploadingDialog.setOnCancelListener(new DialogInterface.OnCancelListener(){
          public void onCancel(DialogInterface dialog) {
              myTask.cancel(true);
              //finish();
          }
    });

That way when I press the back button, the above OnCancelListener cancels both dialog and task. Also you can add finish() if you want to finish the whole activity on back pressed. Remember to declare your async task as a variable like this:

    MyAsyncTask myTask=null;

and execute your async task like this:

    myTask = new MyAsyncTask();
    myTask.execute();

How to cancel or stop AsyncTask?

On your button click write the code

task.cancel(true);

where task is the reference of the async task you have created and started

Ideal way to cancel an executing AsyncTask

Just discovered that AlertDialogs's boolean cancel(...); I've been using everywhere actually does nothing. Great.

So...

public class MyTask extends AsyncTask<Void, Void, Void> {

    private volatile boolean running = true;
    private final ProgressDialog progressDialog;

    public MyTask(Context ctx) {
        progressDialog = gimmeOne(ctx);

        progressDialog.setCancelable(true);
        progressDialog.setOnCancelListener(new OnCancelListener() {
            @Override
            public void onCancel(DialogInterface dialog) {
                // actually could set running = false; right here, but I'll
                // stick to contract.
                cancel(true);
            }
        });

    }

    @Override
    protected void onPreExecute() {
        progressDialog.show();
    }

    @Override
    protected void onCancelled() {
        running = false;
    }

    @Override
    protected Void doInBackground(Void... params) {

        while (running) {
            // does the hard work
        }
        return null;
    }

    // ...

}

Cancel AsyncTask after some time

You need a thread that cancels your task after a certain amount of time. That Thread could look like this:

public class TaskCanceler implements Runnable{
    private AsyncTask task;

    public TaskCanceler(AsyncTask task) {
        this.task = task;
    }

     @Override
     public void run() {
        if (task.getStatus() == AsyncTask.Status.RUNNING )
            task.cancel(true);
     }
}

And when you call your AsyncTask, you need to run the cancle task after a certain amount of time (=the timeout, in this case 20 sec)

private Handler handler = new Handler();
private TaskCanceler taskCanceler;
...
LoadData task = new LoadData();
taskCanceler = new TaskCanceler(task);
handler.postDelayed(taskCanceler, 20*1000);
task.execute(...)

It's a good idea if you clean this up on cancel or finish with

if(taskCanceler != null && handler != null) {
     handler.removeCallbacks(taskCanceler);
}

You can of course wrap this in an custom implementation of AsyncTask. I've used this pattern many times and it works like a charm. One thing to note, in rare cases the handler would not start, I suspect if you create it in the wrong context it will not survive in certain instances, so I forced the handler to be an the UI Thread with handler= new Handler(Looper.getMainLooper());

Android Async task cancel/stop

keep reference to AsyncTask object as instance variable and then in onDestroy() do this

@Override
protected void onDestroy() {
    if (mTask != null) {
        mTask.cancel(true);
    }

    super.onDestroy();
}

How to cancel AsyncTask and execute it again with new parameters?

You have to call the cancel on the AsynTask to cancel it.

It meant that control wont go in the onPostExecute(result) if you have cancelled it when control is in doInBackGround(..)

and you have to check that your asynctask has cancelled or not. You can do this isCancelled()

See here : http://developer.android.com/reference/android/os/AsyncTask.html#cancel(boolean)

See here : http://developer.android.com/reference/android/os/AsyncTask.html#isCancelled()

---

Related Topics