java - 时间选择器每分钟执行计划任务，直到达到设定时间，而不是仅在设定时间执行

Question

我正在使用一个时间选择器，用户将在其中设置时间，然后在该时间显示一条 toast 消息。问题是每分钟都会显示一次 toast ，直到达到设定的时间。

代码如下:

public class ManualControlsFragment extends Fragment {

 private TimePicker tp;
    private Calendar calendar;
    long pickedTimeInMillis;
    long timeDifference;

//some Fragment methods

public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

       View view = inflater.inflate(R.layout.fragment_manual_controls, container, false);

       tp = (TimePicker) view.findViewById(R.id.lightTimePickerStart);
       tp.setIs24HourView(true);
       calendar = Calendar.getInstance();

       tp.setOnTimeChangedListener(new TimePicker.OnTimeChangedListener() {
            @Override
            public void onTimeChanged(TimePicker view, int hourOfDay, int minute) {

                calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                calendar.set(Calendar.MINUTE, minute);
                calendar.set(Calendar.SECOND, 0);
                pickedTimeInMillis= calendar.getTimeInMillis();
                // at this point get the current time
                Calendar cal = Calendar.getInstance();
                // now calculate the difference as the user actually selected a time
                timeDifference = pickedTimeInMillis - cal.getTimeInMillis();

                new Handler(Looper.getMainLooper()).postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        //Do something here
                        Toast.makeText(getActivity().getApplicationContext(), "Bulb is now on", Toast.LENGTH_LONG).show();
                    }
                }, timeDifference);
            }
        });

return view;
    }

我认为这是因为当我向下滚动选择器以选择分钟时，时间选择器中的 onTimeChangedListener 会每分钟注册一次。假设我必须将时间设置为 14:30，而当前时间选择器上的时间为 14:25，我必须将选择器从 25、26、27、28、29 向下滚动，最后滚动到 30 将其设置为14:30。我认为这就是时间选择器每分钟显示 toast 的原因。我怎样才能解决这个问题？而且，我在处理程序中使用 Looper.getMainLooper()) 因为我还有 4 个其他线程在其他 fragment 的后台运行。

Answer 1

尝试这样的操作，mHandler.removeMessages(0); 如果 hundler 已经在运行，它会停止它，并且最后一个不会停止:

 public class ManualControlsFragment extends Fragment {
    private TimePicker tp;
    private Calendar calendar;
    long pickedTimeInMillis;
    long timeDifference;
//some Fragment methods
    Handler mHandler = new Handler(Looper.getMainLooper());

    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_manual_controls, container, false);
        tp = (TimePicker) view.findViewById(R.id.lightTimePickerStart);
        tp.setIs24HourView(true);
        calendar = Calendar.getInstance();
        tp.setOnTimeChangedListener(new TimePicker.OnTimeChangedListener() {
            @Override
            public void onTimeChanged(TimePicker view, int hourOfDay, int minute) {
                calendar.set(Calendar.HOUR_OF_DAY, hourOfDay);
                calendar.set(Calendar.MINUTE, minute);
                calendar.set(Calendar.SECOND, 0);
                pickedTimeInMillis = calendar.getTimeInMillis();
                // at this point get the current time
                Calendar cal = Calendar.getInstance();
                // now calculate the difference as the user actually selected a time
                timeDifference = pickedTimeInMillis - cal.getTimeInMillis();
                mHandler.removeMessages(0);
                mHandler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        //Do something here
                        Toast.makeText(getActivity().getApplicationContext(), "Bulb is now on", Toast.LENGTH_LONG).show();
                    }
                }, timeDifference);
            }
        });
        return view;
    }
}