Android TextView.setText() does nothing in button onClickListener

Question

I am trying to change the text of a TextView after clicking a button. The text will display a countdown of seconds so the setText() function gets called several times inside a loop. The text never changes until after the entire onClickTrain function is finished.

I'm using fragments.

The Log.d(...) displays everything perfectly so I know the process is okay.

public  View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    final View v = inflater.inflate(R.layout.fragment_classification, container, false);
    assert v != null;

    liveView = (TextView)v.findViewById(R.id.textView3);

    View trainButton = v.findViewById(R.id.train);
    trainButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v){
            onClickTrain(v);
        }
    });

    return v;
}

public void onClickTrain(View v) {

    for(int i=0;i<numGestures;i++) {//countdown to train each gesture
        for (int countDown = 3; countDown > 0; countDown--) {//count down from 3

            Log.d("Hold ", ListElements[i] + " in " + String.valueOf(countDown));
            liveView.setText("Hold " + ListElements[i] + " in " + String.valueOf(countDown));

            SystemClock.sleep(1000);//wait 1 second
        }
        fcalc.setTrain(true);
        SystemClock.sleep(100);
        while(fcalc.getTrain()){
            //wait until training data is full
        }
    }
    Log.d("size of train vector: ", String.valueOf(fcalc.samplesClassifier.size()));
    fcalc.Train();
    fcalc.setClassify(true);

}

Any idea why the text is not displaying? I have tried using handlers in several different places.

Any input is appreciated. Thanks.

Answer 1

You can use a handler to add a delay. If you use Thread.Sleep(5000) it will make the UI irresponsive.

new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
      //Do something here
    }
}, 5000);