How to make a Toast in top-level AsyncTask class

Issue

I have a top-level Fetch class that extends AsyncTask and I have a MainActivity. I can't get the Fetch class to make a toast due to not having an instance of the MainActivity or its context. I have tried to pass the MainActivity to the Fetch class but it potentially leaks memory. I have tried setting a WeakReference instance of the context, but I can't make a toast from that.

I have read many other posts about this and most seem to have a static inner-class but mine is top-level and I would prefer to keep it that way.

The MainActivity creates an instance of Fetch and then executes it.

public class Fetch extends AsyncTask<Void, Integer, List<List<String>>>
    {
    @Override
    protected void onPreExecute()
        {
        super.onPreExecute();
        }
    @Override
    protected List<List<String>> doInBackground(Context... params)
        {
        // run tasks
        }
    @Override
    protected void onProgressUpdate(Integer... progress)
        {
        }
    @Override
    protected void onPostExecute(List<List<String>> result)
        {
        super.onPostExecute(result);
        }
    }

Solution

One way, in doInBackground:

runOnUiThread(new Runnable() {
public void run() {
        Toast.makeText(<your class name>.this, "hello", Toast.LENGTH_SHORT).show();
    }
});

Or in onPostExecute(which invoked on the UI thread after the background computation finishes)

Toast.makeText(<your class name>.this, "hello", Toast.LENGTH_SHORT).show();

Edited: if you want to pass context to AsyncTask，you could do like:

public class MyAsyncTask extends AsyncTask<Void, Integer, List<List<String>>>

    private final Context mContext;

    public MyAsyncTask(final Context context) {
         mContext = context;
    }
}

And in MainActivity ：

final MyAsyncTask task = new MyAsyncTask(getApplicationContext());
task.execute();

Edited again: I tested WeakReference successfully.

public class ExampleAsyncTask extends AsyncTask {
    private WeakReference<Context> contextRef;

    public ExampleAsyncTask(Context context) {
        contextRef = new WeakReference<>(context);
    }


    @Override
    protected void onPostExecute(Object result) {
        Context context = contextRef.get();
        if (context != null) {
            Toast.makeText(context, "hello", Toast.LENGTH_SHORT).show();
        }
    }
}

In MainActivity:

  new ExampleAsyncTask(MainActivity.this).execute();

Answered By - navylover