How to delay a loop in android without using thread.sleep?

Question

I wanted to delay a for loop without using Thread.sleep because that method make my whole application hang. I tried to use handler but it doesn't seems to work inside a loop. Can someone please point out the mistake in my code.

public void onClick(View v) {      if (v == start)     {            for (int a = 0; a<4 ;a++) {           Handler handler1 = new Handler();          handler1.postDelayed(new Runnable() {          ImageButton[] all= {btn1, btn2, btn3, btn4};         btn5 = all[random.nextInt(all.length)];         btn5.setBackgroundColor(Color.RED);               @Override              public void run() {               }              }, 1000);         }          }      } 

Basically what I wanted to do is that I got 4 ImageButton and I change each of their background to red by using a loop in order. Thats why I need a delay inside my loop, if not all the ImageButton will just directly turn red without showing which ImageButton turn first.

Answer 1

Your for loop should be:

final ImageButton[] all= {btn1, btn2, btn3, btn4}; Handler handler1 = new Handler(); for (int a = 1; a<=all.length ;a++) {     handler1.postDelayed(new Runnable() {           @Override          public void run() {               ImageButton btn5 = all[random.nextInt(all.length)];               btn5.setBackgroundColor(Color.RED);          }          }, 1000 * a);     }  } 

This way it achieves your desired behavior of staggering the color change.

Edited for syntax

Answer 2

You can use a Handler instead of for loop. You should not call Thread.sleep() on the UI thread.

final Handler handler = new Handler(); Runnable runnable = new Runnable() {      @Override     public void run() {         // do something         handler.postDelayed(this, 1000L);  // 1 second delay     } }; handler.post(runnable);