Update Android UI from a thread in another class

android, asynchronous, handlers, multithreading, runnable

Solution

What I'm trying to do is update the UI from a thread which has been created in another class. I've seen all of the suggestions, such as async, handlers, runnable, etc... but I've having real trouble implementing them in separate classes.

Generally for your goal i recommend to you use:

- `AsyncTask`

- `IntentService` with `ResultReceiver`

I don't think that its too tricky. Absolutely not. If you have it as separated class(es) and not as inner class(es) in some `Activity` class so i recommend to use constructor where you will pass context, widgets, generally whatever you want and then in correct methods(which allows UI update) update your `UI`.

I'm doing it because i like when i have clean classes(so UI class have only UI implementations and logic is positioned separately).

Example:

public class TaskExample extends AsyncTask<Void, Integer, Void> {

   private Context c;
   private Button b;

   public TaskExample(Context c, Button b) {
      this.c = c;
      this.b = b;
   }

   protected Void doInBackground(Void... params) {
      // some work
      if (isSomethingConnected) {
         publishProgress(Constants.IS_CONNECTED);
      }
      return null;
   }

   public void onProgressUpdate(Integer... params) {
       switch (params[0]) {
          case Constants.IS_CONNECTED:
             b.setText("Connected");
          break;
          case Constants.ANOTHER_CONSTANT:
             // another work
          break;
       }
   }  
}

Usage:

public class Main extends Activity implements View.OnClickListener {

   private Button b;

   public void onCreate(Bundle b) {
      super.onCreate(b);
      // initialise widgets and set listeners to appropriate widgets
   }

   public void onClick(View v) {
      switch(v.getId()) {
         case R.id.connectBtn:
            startWorker();
         break;
      }
   }

   private void startWorker() {
      TaskExample te = new TaskExample(this, b);
      te.execute();
   }
}

Problem

Original source