Andorid 开发之子线程更新UI AsyncTask

public class MainActivity extends AppCompatActivity {
    private ProgressBar progressBar;
    private Button btnDownLoad;
    private TextView txtView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView() {
        progressBar = findViewById(R.id.progressBar);
        btnDownLoad = findViewById(R.id.btnDownLoad);
        txtView = findViewById(R.id.txtView);
    }

    public void onDownLoad(View view) {
        new DownLoadTask().execute(20);
    }

    class DownLoadTask extends AsyncTask {
        
        @Override
        protected void onPreExecute() {
            txtView.setText("下载中。。。");
        }

        @Override
        protected Boolean doInBackground(Integer...integers) {
            int progress = integers[0];
            while (true) {
                progress+=5;
                publishProgress(progress);
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (progress > 100) {
                    return true;
                }
            }
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            int progress = values[0];
            progressBar.setProgress(progress);
        }

        @Override
        protected void onPostExecute(Boolean aBoolean) {
            if (aBoolean) {
                txtView.setText("下载完毕！");
            }
        }
    }
}