How to update a TextView in an activity constantly in an infinite loop?

Question

I have an activity which has a TextView, and I want to update the text constantly..

In Java I could just make an infinite while loop, and just set the text each iteration.

But when I try to do that in Android, it shows a black screen, and doesn't even load the activity.

I put the infinite in the onCreate method, perhaps that's why it crashes..but if it is, where should I put it?

You shouldn't have an infinite loop, at least not on the main thread. What's the purpose of it? :-) — karllindmark, Jan 12 '13 at 16:08
Well, I want something to update infinitely ( or at least constantly) — aclowkay, Jan 12 '13 at 16:21
similar: http://stackoverflow.com/questions/11295152/android-running-infinite-loop || http://stackoverflow.com/questions/1099640/main-loop-in-android — Ciro Santilli OurBigBook.com, Feb 03 '16 at 22:13
http://stackoverflow.com/questions/8123231/android-count-down-timer-in-background || http://stackoverflow.com/questions/5464990/how-to-execute-background-job-that-update-ui-view-android — Ciro Santilli OurBigBook.com, Mar 02 '16 at 10:35

score 14 · Accepted Answer · edited Feb 05 '16 at 20:53

14

use Handler and a separate thread/runnable for updating TextView constantly instead of While loop :

Handler handler=new Handler();
handler.post(new Runnable(){ 
    @Override
    public void run() {
        // upadte textView here
        handler.postDelayed(this,500); // set time here to refresh textView
    }
});

edited Feb 05 '16 at 20:53

Ciro Santilli OurBigBook.com

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answered Jan 12 '13 at 16:11

ρяσѕρєя K

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3

If you are going to refer to handler as part of that closure, you need to delcare it final. – MattD Mar 02 '14 at 02:20

Ciro Santilli OurBigBook.com · Answer 2 · 2020-10-17T08:17:38.300

Minimal working example

Based on https://stackoverflow.com/a/14295193/895245:

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.widget.TextView;

public class Main extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        final int i = 0;
        final TextView textView = new TextView(this);
        textView.setText(String.format("%d", i));
        setContentView(textView);
        final Handler handler = new Handler();
        class MyRunnable implements Runnable {
            private Handler handler;
            private int i;
            private TextView textView;
            public MyRunnable(Handler handler, int i, TextView textView) {
                this.handler = handler;
                this.i = i;
                this.textView = textView;
            }
            @Override
            public void run() {
                this.handler.postDelayed(this, 500);
                this.i++;
                this.textView.setText(String.format("%d", i));
            }
        }
        handler.post(new MyRunnable(handler, i, textView));
    }
}

You can just copy paste this into the main activity generated by android create project [...], and you will see a counter on your app.

Tested on Android 22.

How to update a TextView in an activity constantly in an infinite loop?

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