Question

How do i change the background of a LinearLayout via setBackgroundColor() by another thread?

I learned, that the Android UI Framework is not threadsafe, so you can’t change UI elements by another Thread than the UI thread.

My goal is to create a strobe light effect by calling the setBackgroundColor() method with changing colors (in this case black/white/black/ect,) on a LinearLayout which fills the entire screen.

Answer 1

One way is to use Handler with message queues. You instantiate the Handler in the main UI thread, then use obtainMessage() to send messages to the Handler. So an example would be like

public final Handler updateTextView = new Handler(){
   @Override
   public void handleMessage(Message msg)
   {
      if(msg.what == UPDATE_TEXT){
          myTextView.setText("arg1 = " + msg.arg1 +
                             "; arg2 = " + msg.arg2 + "; " + (String)msg.obj);
      }
   }
}

Then in your thread you can call:

String myString = new String("test");
updateTextView.obtainMessage(UPDATE_TEXT, 10, 20, myString).sendToTarget();

The result if called once will be myTextView now says “arg1 = 10; arg2 = 20; test”.