单击按钮时，倒数计时器取消会使应用程序崩溃

Question

我正在尝试创建一个 countDownTimer 但是，每当我单击该按钮时，应用程序就会崩溃。我希望如果我点击 player1 按钮 player2 倒计时 应该暂停，反之亦然 player2.

我得到的错误：

Attempt to invoke virtual method 'void android.os.CountDownTimer.cancel()' on a null object reference

这是代码

public class Timer extends AppCompatActivity {

    Button player1, player2;
    long incrementTime = 3000;
    int time;
    long timeinLong;
    ImageButton pause;
    CountDownTimer player1count, player2count;

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

        player1 = findViewById(R.id.player1);
        player2 = findViewById(R.id.player2);

        Intent intent = getIntent();
        time = intent.getIntExtra("time", 0);
        timeinLong = time * 60000;

        int minutes = (int) (timeinLong / 1000) / 60;
        int seconds = (int) (timeinLong / 1000) % 60;

        String timeFormatted = String.format(Locale.getDefault(), "%02d:%02d", minutes, seconds);

        player1.setText(timeFormatted);
        player1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startCountDown(player1);
                player2count.cancel();

            }
        });
        player2.setText(timeFormatted);
        player2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startCountDown2(player2);
                player1count.cancel();
            }
        });

    }

    private void startCountDown(final Button button) {
        player1count = new CountDownTimer(timeinLong, 1000) {
            @Override
            public void onTick(long millisUntilFinished) {
                timeinLong = millisUntilFinished;
                updateCountDownText(button);
            }

            @Override
            public void onFinish() {
                timeinLong = 0;
                updateCountDownText(button);
            }
        }.start();
    }

    private void startCountDown2(final Button button) {
        player2count = new CountDownTimer(timeinLong, 1000) {
            @Override
            public void onTick(long millisUntilFinished) {
                timeinLong = millisUntilFinished;
                updateCountDownText(button);
            }

            @Override
            public void onFinish() {
                timeinLong = 0;
                updateCountDownText(button);
            }
        }.start();
    }

    private void updateCountDownText(Button button) {
        int minutes = (int) (timeinLong / 1000) / 60;
        int seconds = (int) (timeinLong / 1000) % 60;

        String timeFormatted = String.format(Locale.getDefault(), "%02d:%02d", minutes, seconds);

        button.setText(timeFormatted);

        if (timeinLong < 30000) {
            button.setTextColor(Color.RED);
        } else {
            button.setTextColor(Color.BLACK);
        }
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (player1count != null) {
            player1count.cancel();
        }
    }
}

Answer 1

点击侦听器调用时您没有初始化它
我通过在 .cancel 行
上添加 try catch 自己修复了它或设置

if (player1count != null)
...

Answer 2

player2count 仅在 startCountDown2 内部初始化，仅在 player2.setOnClickListener 内部调用。因此，如果您在单击 player2 按钮之前单击 player1 按钮，您将得到一个 NullPointerException，因为在尚未初始化的 player2count 是不允许的。为了防止这种情况发生，在这种情况下只检查 null 是合适的：

if (player2count != null) {
  player2count.cancel();
}

Answer 3

只是不要取消定时器，除非它们被初始化，它会带来 NPE，所以检查它们是否在两个播放器中都不为空，如下所示

    player1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            startCountDown(player1);
            if (player2count != null)
                player2count.cancel();

        }
    });
    player2.setText(timeFormatted);
    player2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            startCountDown2(player2);
            if (player1count != null)
                player1count.cancel();
        }
    });

单击按钮时，倒数计时器取消会使应用程序崩溃

Countdowntimer cancel crashes the app when click on button

android

android-studio

countdowntimer