Android TextView。setText()在按钮onClickListener中不执行任何操作

我试图在单击按钮后更改TextView的文本。文本将显示秒倒计时,因此 setText() 函数在循环内被调用多次。文本在整个过程结束后才会更改 onClickTrain

Log.d(…)完美地显示了所有内容,因此我知道这个过程是正常的。

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);

}

知道文本为什么没有显示吗?我尝试在几个不同的地方使用处理程序。