Question

I display an Alertbox with ok or cancel.
I want to implement an asynch task on the press of OK. Havent done asynch and been struggling with it for awhile. I dont understand where the asych class goes also. Does it go outside the method that is being executed or outside of it? Current code as follows:

 private abstract  class DoAsynchTask extends AsyncTask<Void,Void,Void> 
 {
  protected  void doInBackground()
  {
   Drawable drawable= getImage(imageSelect);     
   MakeWallPaper(drawable,1);
  }

  /* protected void onProgressUpdate(Integer... progress) 
  {
   setProgress(progress[0]);
  }*/

  protected void onPostExecute() 
  {
   Toast.makeText(getApplicationContext(), "Wallpaper Saved.",Toast.LENGTH_LONG).show();      
   AlertDialogProcessing=0;
  }
 }

 public void getWallpaper(final View v)
 {
  if(AlertDialogProcessing==0)
  {  
   final String title="Set Image to Wallpaper";
   final String message="Press OK to set as Wallpaper or CANCEL.\nWait after pushing OK.";
   final String ok="OK";
   final String cancel="CANCEL";
   final AlertDialog.Builder alertbox = new AlertDialog.Builder(this);
   alertbox.setCancelable(true);
   alertbox.setIcon(android.R.drawable.ic_dialog_alert);
   alertbox.setTitle(title);
   alertbox.setMessage(message);
   alertbox.setNegativeButton(cancel, null);
   final AlertDialog dlg = alertbox.create();

   alertbox.setPositiveButton(ok,new DialogInterface.OnClickListener()
   {  
     public void onClick(DialogInterface dlg, int which)
     {  
       DoAsynchTask.execute(null,null,null);  //<<<<Wrong
       dlg.dismiss();
       Vibrate(ClickVibrate); 
     } 
    });
    alertbox.setNegativeButton(cancel,new DialogInterface.OnClickListener(){ public  void onClick(DialogInterface arg0, int arg1){AlertDialogProcessing=0;                     
     Vibrate(ClickVibrate); } });
 alertbox.show();
    }
   }

Answer 1

There’s a couple problems in the code.

1) First of all, the compiler is probably giving you this message:

The type MyActivity.DoAsynchTask must implement the inherited abstract
method
AsyncTask.doInBackground(Void…) MyActivity.java

If you look closely at the error message, you’ll realize that what you defined was this:

protected  void doInBackground() {

which is not what is needed. Even though it might seem silly, when your AsyncTask subclass takes Void as the generic parameter types, that means that doInBackground() must look like this:

protected Void doInBackground(Void... arg0) {

The compiler complains because you haven’t implemented that (exact) method. When you inherit from an abstract class, and fail to implement all of its required/abstract method(s), then you can only get it to compile by marking the subclass as abstract, too. But, that’s not really what you want.

So, just change your code to (remove abstract from your class):

private class DoAsynchTask extends AsyncTask<Void,Void,Void> 

and

protected Void doInBackground(Void... arg0) {
{
   Drawable drawable= getImage(imageSelect);     
   MakeWallPaper(drawable,1);
   return null;
}

2) And the second problem, as others have pointed out, is that you must start your task with:

new DoAsynchTask().execute();

not

DoAsynchTask.execute(null,null,null);   

Your code would only be correct if execute() was a static method in AsyncTask, which it’s not. In order to invoke the non-static execute() method, you first need a new instance of the DoAsynchTask class. Finally, the null, null, null parameter list is also not necessary, although I don’t think it will cause the code to fail either.