why a new Thread can touch view

Asked Feb 08 '19 at 14:18

Active Feb 08 '19 at 14:18

Viewed 34 times

as we know in Android applications we can touch views just from Main/UI Thread and otherwise an CalledFromWrongThreadException throws with below message:

android.view.ViewRootImpl$CalledFromWrongThreadException:
Only the original thread that created a view hierarchy can touch its views.

but when I touch just 1 time at onCreate(), this Exception does not throw and "Hello Again!" sets on TextView

 TextView tv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    tv = findViewById(R.id.tv);

    new Thread(new Runnable() {
        @Override
        public void run() {
            tv.setText("Hello Again!");
        }
    }).start();
}

Do you know why?

asked Feb 08 '19 at 14:18

beigirad

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It looks like your runnable completes before onStart method, so may be view for that moment are not actually owned be Main/UI Thread. – Raskilas Feb 08 '19 at 14:35
@Raskilas It means `onCreate()` does not run on MainThread? I copied this snipped code to `onStart()` too. and it ran correctly. – beigirad Feb 08 '19 at 14:47
I suppose that your code just add Runnable to event queue, and it won't work if you will the same in AsyncTask in doInBackground(). – Raskilas Feb 08 '19 at 14:59
Hmm... what is `tv's` original text, as specified in the layout file? It may be important. – greeble31 Feb 08 '19 at 17:29
the original text is default "Hello world!" and there is no problem in layout and inflating and etc. @greeble31 – beigirad Feb 08 '19 at 18:18
Would you humor me and try it with "Hello Again Extra Text!"? – greeble31 Feb 08 '19 at 18:24
@greeble31 =)))) – beigirad Feb 08 '19 at 18:27
What does that mean? – greeble31 Feb 08 '19 at 18:31

why a new Thread can touch view

0 Answers0