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.

you don't need a for loop. you can use a Handler itself – Raghunandan Jan 03 '14 at 03:55 — Raghunandan, Jan 03 '14 at 03:55

sddamico · Accepted Answer · 2014-01-03T04:18:39.230

46

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

edited Jan 03 '14 at 04:18

answered Jan 03 '14 at 04:05

sddamico

2,130
16
13

It worked but I have another problem. I get an syntax error at the `ImageButton btn5 = all[random.nextInt(all.length)];` when I use your code. It seems like I had to put `final ImageButton[] all= {btn1, btn2, btn3, btn4};` for it to work. – user3153613 Jan 03 '14 at 04:14
Edited with `final` added to the array. – sddamico Jan 03 '14 at 04:19
1

this is not working because a is not specific for each runable – Mahdi Oct 16 '16 at 13:29
TextView number = findViewById(R.id.textView2); Handler handler1 = new Handler(); for (int a = 1; a<=3 ;a++) { handler1.postDelayed(new Runnable() { @Override public void run() { number.setText(String.valueOf(numbersArray[a])); } }, 1000 * a); } It says, Textview AND a needs to be decalred final! Now, how would i increase if a is final? Any ideas! – user3156040 Aug 27 '19 at 08:45

score 17 · Answer 2 · edited Feb 26 '20 at 13:53

17

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);

edited Feb 26 '20 at 13:53

Abandoned Cart

4,512
1
34
41

answered Jan 03 '14 at 03:58

Raghunandan

132,755
26
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256

can you give me an example of using `Handler` instead of loop for my code – user3153613 Jan 03 '14 at 04:05
@user3153613 use the above . that ihas 1 second delay and then instead of do something. set the background color to button – Raghunandan Jan 03 '14 at 04:07
1

it keeps on going untill you stop the handler by `m_hnbdler.removeCallbacks(m_handlerTask)` – Raghunandan Jan 03 '14 at 04:10
@user3153613 how do you initialize your buttons? – Raghunandan Jan 03 '14 at 04:41
This generates an error that `runnable` may not have been initialized, but you can replace the reference inside `run` with `this`. @Raghunandan I believe you meant `handler.removeCallbacks(runnable);` – Abandoned Cart Feb 25 '20 at 17:39
After looking this over a little more, I also think you want to call `handler.post(runnable);` rather than `runnable.run();` initially. – Abandoned Cart Feb 25 '20 at 17:57
@AbandonedCart corrected it. it was a long time back thanks for correcting. – Raghunandan Feb 26 '20 at 07:06
@Raghunandan You copied in the **optional** suggestion, but did not address the **error** of attempting to call the variable inside its initialization. I have edited the answer to fix it. – Abandoned Cart Feb 26 '20 at 13:57

Cody · Answer 3 · 2017-02-06T09:25:12.930

7

The following code doing the task in every second:

final Handler handler = new Handler();
Runnable task = new Runnable() {
    @Override
    public void run() {
        Log.d(TAG, "Doing task");
        handler.postDelayed(this, 1000);
    }
};
handler.post(task);

edited Feb 06 '17 at 09:25

answered Mar 01 '16 at 12:47

Cody

4,353
4
39
42

score 1 · Answer 4 · edited Jun 06 '15 at 02:58

Try this :

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};
                @Override
                public void run() {
                    btn5 = all[random.nextInt(all.length)];
                    btn5.setBackgroundColor(Color.RED);
                }
            }, 1000);
        } 
    }
}

Example for Delay :

final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
    @Override
    public void run() {
        // Do something after 5s = 5000ms
        buttons[inew][jnew].setBackgroundColor(Color.Red);
    }
}, 5000);

just call public void run() inside the loop and make parameters for your button index or button names — Imran Ali Khan, Jan 03 '14 at 04:00

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

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