java - CountdownTimer 崩溃应用程序。尝试更新 UI 线程

Question

我希望倒数计时器在一个单独的线程上，并让它在每次滴答时更新 UI。每次我点击启动时，应用程序都会关闭，并且我会收到“应用程序已停止”错误消息。

public class Activity_MultiplayerGame extends AppCompatActivity {

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

public void btnStart_onClick(View view){
    CountDownTimer timer = new CountDownTimer(15000, 1000){

        @Override
        public void onTick(final long millisUntilFinished) {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    TextView countdownText = (TextView) findViewById(R.id.countdown);
                    Integer timeUntilFinished = (int) millisUntilFinished/1000;
                    countdownText.setText(timeUntilFinished);
                }
            });
        }

        @Override
        public void onFinish() {
            TextView countdownText = (TextView) findViewById(R.id.countdown);
            countdownText.setText("Finished");
        }
    };

    timer.start();
}
}

我假设创建 CountDownTimer 会为其提供自己的线程？

Answer 1

你可以使用 Handler 。我给你写了一个例子

此代码每隔一秒增加一个计数器，并在 textView 上显示和更新计数器值。

public class MainActivity extends Activity {


    private Handler handler = new Handler();
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView) findViewById(R.id.text);
        startTimer();
    }


    int i = 0;
    Runnable runnable = new Runnable() {
        @Override
        public void run() {
            i++;
            textView.setText("counter:" + i);
            startTimer();
        }
    };

    public void startTimer() {
        handler.postDelayed(runnable, 1000);
    }

    public void cancelTimer() {
        handler.removeCallbacks(runnable);
    }

    @Override
    protected void onStop() {
        super.onStop();
        cancelTimer();
    }
}