AsyncTask not generic?

Question

Hi When I try to compile to following code, I get two errors:

Description Resource Path Location Type Syntax error on token "void", invalid Expression AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 19 Java Problem

Description Resource Path Location Type The type AsyncTask is not generic; it cannot be parameterized with arguments AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 25 Java Problem

package org.me.asynctask;

import android.app.Activity; import android.content.Context; import android.os.Bundle; import android.widget.TextView; import android.widget.Toast; import android.os.; public class AsyncTask extends Activity { /* Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main);

    TextView mytextview = new TextView(this);
    TextView secondtextview = new TextView(this);

    new MyAsyncClass().execute(mytextview, void, secondtextview);

}



private class MyAsyncClass extends AsyncTask<TextView, Void, Void> {
 protected TextView doInBackground(TextView tv)
 {
  tv.setText("Your AsyncTask was successful!");
  return tv;
 }


 protected void onPostExecute(TextView Result)
 {
  Context context = context.getApplicationContext();
        Toast mytoast = Toast.makeText(context, "AsyncTask processing complete", Toast.LENGTH_LONG);
        mytoast.show();
 }

}

Obviously AsyncTask IS a generic (http://developer.android.com/reference/android/os/AsyncTask.html#execute(Params...) so why do i get those errors?

Answer 1

You are overriding the AsyncTask methods with the wrong types. It is defined as:

AsyncTask<Params, Progress, Result>

and the doInBackground method is defined as protected abstract Result doInBackground (Params... params)

so according to your definition, you should have protected Void doInBackround(TextView... params);

onPostExecute is also incorrectly defined.

Answer 2

There are several problems, two of which are:

1. You defined a class AsyncTask, which hides/collides with android.os.AsyncTask. Maybe you intended to call it AsyncTaskDemo.java or AsyncTaskActivity.java or something.

2. You're trying to change the UI from the background thread by calling tv.setText inside of doInBackground. That defeats the purpose of AsyncTask. Code in doInBackground shouldn't be touching the main (or 'UI') thread. For mid-task updates inside of doInBackground, use AsyncTask.publishProgress.