Activity -> AsyncTask -> BroadcastReceiver -> Update UI

Question

I am starting an AsyncTask from an Activity. When, the AsyncTask completes its execution I need to send a broadcast which needs to call Activity method to update the UI.

Any good approach to achieve this.

Answer 1

Yes.

If the AsyncTask is an inner class of your Activity then it has access to any member variables and your Activity methods. If it isn't then you can simply pass variables to its constructor or even a reference to the Activity to call Activity methods from onPostExecute(). Without any code its hard to say much else.

To pass an instance of your Activity and use its methods if its a separate class then you can create a constructor and do something like

    public class MyTask extends AsyncTask<...>  // add your params
{
    private MyActivity activty;

    public MyTask (MyActivity act)
    {
        this.activty = activty;
    }

    // ...
}

and in onPostExecute() add something like

activity.myMethod();

and call the task like

MyTask task = new MyTask(this); // pass a reference of the activity
task.execute();  // add params if needed

If the AsyncTask is a separate file from the Activity then you can see this answer on how to use an interface for a callback

Answer 2

Please use Interface.

interface INotifyChange {
    void notifyChange(); // You can use params to transfer data :D
}

In Activity you should implements this interface.

YourActivity  extends Activity implements INotifyChange {

    @Override
    public void notifyChange() {
        // Right here, you can Update UI.
    }
}

When you create new instance of AsyncTask

Example:

YourAsyncTask mTask = new YourAsyncTask(this); // You put INotifyChange

In YourAsyncTask

private INotifyChange iNotifyChange;
public YourAsyncTask(INotifyChange iNotifyChange) {
    this.iNotifyChange = iNotifyChange;
}

// When you complete doInBackground or anywhere you want to Update UI please use iNotifyChange.notifyChange()

Example:

@Override
public void onPostExecute(ResultType mResult) {
    iNotifyChange.notifyChange();
}

By this way I often use to update progress bar. In this case, I use parameter in my method:

Example:

iNotifyChange.notify(progress);

Answer 3

Have you considered overwriting the onPostExecute() method of the AsyncTask to update the UI? Try something like this:

AsyncTask<String, Void, Bitmap> task = new AsyncTask<String, Void, Bitmap>(imageView)
{
    private ImageView imageView;

    public AsyncTask(ImageView imageView)
    {
         this.imageView = imageView;
    }

    @Override
    protected Bitmap doInBackground (String... params)
    {
        if(params.length > 0)
        {
            String filePath = params[0];

            // Load Bitmap from file

            return bitmap;
        }
    }

    @Override
    protected void onPostExecute(Bitmap result)
    {
       imageView.setImageBitmap(result);
    }
}
task.execute(filePath);