Android Error: Only the original thread that created a view hierarchy can touch its views

Question

Getting an error: android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
I really dont have a clue why.

  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button generate = (Button) findViewById(R.id.gen);
    final TextView dice1 = (TextView) findViewById(R.id.dice1);
    final TextView dice2 = (TextView) findViewById(R.id.dice2);
    final TextView dice3 = (TextView) findViewById(R.id.dice3);


    generate.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {           
            dice1.setText(" ");
            dice2.setText(" ");
            dice3.setText(" ");         
            Thread thread = new Thread()
            {
                @Override
                public void run() {
                    try {
                        while(true) {
                            sleep(2000);
                            setText("lol", "lol", "lol");
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            };
            thread.start();             
        }

    });
}
public void setText(String d1, String d2, String d3){
    dice1.setText(d1);
    dice2.setText(d2);
    dice3.setText(d3);  
}

Thanks for helping.

score 5 · Accepted Answer · answered Jun 18 '13 at 19:04

You have this error because you manipulate views in another thread than the UI thread. Your setText method modify the text of 3 TextViews (dice1, dice2, dice3).

You should call this method with runOnUiThread like this:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Button generate = (Button) findViewById(R.id.gen);
    final TextView dice1 = (TextView) findViewById(R.id.dice1);
    final TextView dice2 = (TextView) findViewById(R.id.dice2);
    final TextView dice3 = (TextView) findViewById(R.id.dice3);

    generate.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {           
            dice1.setText(" ");
            dice2.setText(" ");
            dice3.setText(" ");         
            Thread thread = new Thread()
            {
                @Override
                public void run() {
                    try {
                        while(true) {
                            sleep(2000);
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    setText("lol", "lol", "lol");
                                }
                            });
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            };
            thread.start();             
        }

    });
}
public void setText(String d1, String d2, String d3){
    dice1.setText(d1);
    dice2.setText(d2);
    dice3.setText(d3);  
}

sleep inside a thread is a bad design. http://developer.android.com/training/articles/perf-anr.html — Raghunandan, Jun 18 '13 at 20:05
@Raghunandan If you call _sleep()_ on the main thread yes, but not in this case. However it's sure that using an [AsynTask](http://developer.android.com/reference/android/os/AsyncTask.html) for example is probably better than create a Thread each time the user clicks on 'generate' button... — Donkey, Jun 18 '13 at 20:27
If you implement `Thread or HandlerThread`, be sure that your UI thread does not block while waiting for the worker thread to complete— `do not call Thread.wait() or Thread.sleep()`. Quoting from doc. — Raghunandan, Jun 18 '13 at 20:28
Yes, and it means "don't call _Thread.wait()_ on the UI thread waiting for another thread to call _Thread.notify()_ for instance. Calling _Thread.sleep()_ (or _Thread.wait()_) on another thread than the UI thread won't cause an ANR. — Donkey, Jun 18 '13 at 20:52
it blocks the worker thread. so it is not good. i am not saying it will cause anr. — Raghunandan, Jun 18 '13 at 20:53

score 2 · Answer 2 · edited May 23 '17 at 11:48

You are, literally, trying to set fields on your view from the wrong thread. Your OnClickListener creates a new thread, but only the thread that created a view and its hierarchy may alter those views.

You might refactor to use http://developer.android.com/reference/java/util/concurrent/ScheduledThreadPoolExecutor.html

Alternatively, you could just wrap your setter code to be inside of a runOnUiThread block. There's an example on this site, along with a caution of why this might not be a good idea: Android: RunOnUiThread vs AsyncTask.

score 1 · Answer 3 · answered Jun 18 '13 at 18:59

1

You are setting setText on a thread apart. Put the method calling manipulating UI components inside a runOnUiThread block.

answered Jun 18 '13 at 18:59

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Android Error: Only the original thread that created a view hierarchy can touch its views

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