实现Handlers的基本方式

Question

我在处理程序上有这个示例应用程序，它在特定时间触发一个日志，但是当我单击我的开始按钮时它似乎不起作用。下面是我的代码。

public class Main extends Activity {
    private long selectedTimeInMills;
    private Handler handler;
    private static final Calendar CALENDAR = Calendar.getInstance();
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        TimePicker timepicker = (TimePicker) findViewById(R.id.timePicker1);
        final TextView timeText = (TextView) findViewById(R.id.time);

        Button start = (Button) findViewById(R.id.button1);
        handler = new Handler();
        String textTime = formatDate(CALENDAR.getTimeInMillis(), "hh:mm a");
        timeText.setText(textTime);

        timepicker.setOnTimeChangedListener(new OnTimeChangedListener() {

            public void onTimeChanged(TimePicker view, int hourOfDay, int minute) {
                CALENDAR.set(Calendar.HOUR_OF_DAY, hourOfDay);
                CALENDAR.set(Calendar.MINUTE, minute);
                selectedTimeInMills = CALENDAR.getTimeInMillis();
                String textTime = formatDate(CALENDAR.getTimeInMillis(), "hh:mm a");
                timeText.setText(textTime);
            }
        });

        start.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                Runnable runnable =  new Runnable() {

                    public void run() {
                        Log.d("HandlerCheck", "Handler Fired! @ ("+selectedTimeInMills+") "+formatDate(selectedTimeInMills, "hh:mm a"));
                    }
                };
                boolean flag = handler.postAtTime(runnable, selectedTimeInMills);

                Toast.makeText(Main.this, "Handler is Fired?:: "+flag, Toast.LENGTH_LONG).show();
            }


        });

    }
}

注意：当我单击按钮并实现 handler.postAtTime() 时，它会返回 true，但即使我已将时间选择器设置为距当前时间 1 分钟，它仍然不会显示登录 DDMS '不触发 DDMS 上的日志消息

Answer 1

Handler 类中的postAtTime 方法从启动开始计算时间（以毫秒为单位）；不是Calendar 时间（这是您正在传递的时间）。您应该改用SystemClock.uptimeMillis() 来计算时间。

或者，您可以使用postDelayed 函数在设定的时间段（以毫秒为单位）后调用 Runnable 对象。

// Introduce a new private variable
private long delayedTimeInMillis;

// Update delayedTimeInMillis inside onTimeChanged method:
delayedTimeInMillis = selectedTimeInMills - Calendar.getInstance().getTimeInMillis();

// replace handler.postAtTime(runnable, selectedTimeInMills); line with this:
handler.postDelayed(runnable, delayedTimeInMillis)