Question

(programming Android in Eclipse) I am trying to set up a delay in changing the text in a button. I am getting errors only after there is a delay and the text needs to be changed. Here is the simplified code without a while loop:

final Button button_target = (Button) findViewById(R.id.button_target);        
    Thread textChange = new Thread(new Runnable() { 
        public void run(){
            button_target.setText("fog");
            try{
                Thread.sleep(3000);
            }catch(InterruptedException e){}                
        }
    });
    textChange.start();

And now here is the code where a change of text on the button is required after the sleep which now causes and error and exit (forced):

 final Button button_target = (Button) findViewById(R.id.button_target);        
    Thread textChange = new Thread(new Runnable() { 
        public void run(){
            button_target.setText("cat");
            try{
                Thread.sleep(3000);
            }catch(InterruptedException e){}                
            button_target.setText("dog");
        }
    });
    textChange.start();

what am I doing to cause the error? Is there another method that I should do to be able to invoke a sleep or delay to the thread so that a text change operation can be performed?

(the actual code has a while loop but I believe this form puts the error in highlight)

Answer 1

You can’t change UI stuff on a thread like setText(), it must be done on the UIThread. See AsyncTask for more informations :

http://developer.android.com/reference/android/os/AsyncTask.html

Add more information

You can use THREAD_POOL_EXECUTOR with AsyncTask in function of which versions of Android you use like this :

AsyncTask<Void, Void, Void> task = new AsyncTask<Void, Void, Void>() {

    @Override
    protected Void doInBackground(Void... voids) {

        try{
            Thread.sleep(3000);
            }catch(InterruptedException e){} 
        }
    }

    @Override
    protected void onPostExecute(Void result) {
        button_target.setText("dog");
    }

};

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
    task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
} else {
    task.execute();
}