我無法在 JAVA 中使用 Handler 停止 Runnable

Question

我正在嘗試構建一個秒表，並且我有一個名為 start 的按鈕開始計數，在它開始后按鈕的名稱更改為停止，當我按下停止時我想暫停計數，但是當我嘗試運行newHandler.removeCallbacks(updateTimerThread); 程序繼續計數，在重置按鈕上此方法有效。

 public class MainActivity extends AppCompatActivity { Button start_button, reset_button; TextView time_view; long start_time = 0, time_in_miliseconds = 0, update_time = 0, prev_time = 0; final Handler newHandler = new Handler(); Runnable updateTimerThread = new Runnable() { @Override public void run() { time_in_miliseconds = SystemClock.uptimeMillis() - start_time; update_time = time_in_miliseconds + prev_time; int sec = (int) (update_time / 1000); int min = sec / 60; int hour = (int) sec / 3600; sec %= 60; int centisec = (int) (update_time / 10) % 100; time_view.setText(""+hour+":"+String.format("%2d",min)+":"+String.format("%2d",sec)+"."+String.format("%3d",centisec)); newHandler.postDelayed(this, 10); if (start_button.isPressed()) { prev_time += time_in_miliseconds; // Here the Runnable is not stopped newHandler.removeCallbacks(updateTimerThread); //time_view.setText(""+save_hour+":"+String.format("%2d",save_min)+":"+String.format("%2d",save_sec)+"."+String.format("%3d",save_centisec)); } } }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); start_button = (Button) findViewById(R.id.start_button); reset_button = (Button) findViewById(R.id.reset_button); time_view = (TextView) findViewById(R.id.time_view); start_button.setOnClickListener(view -> { start_time = SystemClock.uptimeMillis(); start_button.setText("Stop"); newHandler.postDelayed(updateTimerThread,0); }); if (start_button.isPressed()) { prev_time += time_in_miliseconds; newHandler.removeCallbacks(updateTimerThread); //time_view.setText(""+save_hour+":"+String.format("%2d",save_min)+":"+String.format("%2d",save_sec)+"."+String.format("%3d",save_centisec)); } reset_button.setOnClickListener(view -> { // Here the Runnable is stopped newHandler.removeCallbacks(updateTimerThread); start_time = 0; prev_time = 0; time_view.setText("0:0:0.0"); start_button.setText("Start"); }); } }

Answer 1

請刪除您正在檢查start_button.isPressed()的所有條件塊，它不起作用。 您可以使用附加標志isRunning來指示時鍾是否正在運行：

private boolean isRunning;

start_button.setOnClickListener(view -> {
        if (isRunning) {
            newHandler.removeCallbacks(updateTimerThread);
            start_button.setText("Start");
        } else {
            start_time = SystemClock.uptimeMillis();
            start_button.setText("Stop");
            newHandler.post(updateTimerThread);
        }
        isRunning = !isRunning;
    });

Answer 2

您的計時器需要一些 state。 你可以做這樣的事情（添加'boolean isActive'）：

        Runnable updateTimerThread = new Runnable() {
            boolean isActive = true;
            @Override
            public void run() {
                if (isActive) {
                    time_in_miliseconds = SystemClock.uptimeMillis() - start_time;
                    update_time = time_in_miliseconds + prev_time;
                    // ...
                }
                if (start_button.isPressed()) {
                    isActive = !isActive;
                    // Do some other stuff
                }
            }
        };

或者可以使用 State 模式。