Retry AsyncTask

For example I have following AsyncTask:

  private class MyAsyncTask extends AsyncTask<Void, Void, Boolean> {


     @Override
     protected Void doInBackground(Void... params) {
         try {
             //some code that may throws exception
             return true;
         } catch (IOException ex) {
             return false;
         }
     }


     @Override
     protected void onPostExe开发者_如何学JAVAcute(Boolean param){
        if (!param) {
           AlertDialog.Builder builder = new AlertDialog.Builder(MyActivity.this);
           builder.setMessage("Error");
           builder.setPositiveButton("Retry", new DialogInterface.OnClickListener() {
              public void onClick(DialogInterface dialog, int which) {
                  //I want to retry MyAsyncTask here
              } 
           });
           builder.setNegativeButton("Exit", new DialogInterface.OnClickListener() {
              public void onClick(DialogInterface dialog, int which) {
                 finish();
              } 
           });
           AlertDialog alert = builder.create();
           alert.show();
        }
     }
  }

What is best practice to do this? I'm afraid of recursion this code.

---

You cannot strictly "retry" an instance of AsyncTask. You have to create a new instance and execute it, just as you did the first one. You should not encounter a recursion problem.

---

I retry the code within doInBackground() for x number of times:

 @Override
 protected Void doInBackground(Void... params)
 {
    final int MAX_RETRY=3;
    int iLoop;
    boolean bSuccess=true;
    for (iLoop=0; iLoop<MAX_RETRY; iLoop++)
    {
        try
        {
            //do some code that throw an exception

            //success! exit loop
            iLoop=0;
            break;
        }
        catch (IOException ex)
        {
            bSuccess=false;
        }
    }
    if (iLoop==(MAX_RETRY-1))
    {
        bSuccess=false;
    }
    return bSuccess;
 }

This is also one of those times when the two values of a boolean are inadequate to measure success. You could replace bSuccess with an enum for a third measure of success: retry later.

---

I solved the same problem using BetterASyncTask.

It provides the handy HandleError abstract method, which allows me to catch the exception on the UI thread and decide if retry and how.

---

Please take a look at retryableasynctask and see if it helps.

Usage:

// Params, Progress and Result could be anything, same as a regular AsyncTask
new RetryableAsyncTask<Params, Progress, Result>(myActivity) {
  @Override
  protected void onPreExecute() {
    // write some code here
  }

  @Override
  protected Result doInBackground(Params... params) {
    // execute some expensive task here with your params
    // eg: MyExpensiveTask with method called 'get'

    return MyExpensiveTask.get(params);
  }

  @Override
  protected void onPostExecute(Result result) {
    // write some code here with your result
  }
}.execute(myParams);

Overriding "onError" behaviour

By the default, onError method shows a dialog "Cancel" and "Retry" button options. However, you might wanna do something else when something goes wrong. To do so, override onError with your own error handling.

// Params, Progress and Result could be anything, same as a regular AsyncTask  
new RetryableAsyncTask<Params, Progress, Result>(myActivity) {
  // ...

  @Override
  protected void onError(Throwable error, final Params... params) {
    // write your own error handling
  }
}.execute(myParams);