Android之定时器

android开发中，常用定时器实现方式有以下几种：

1、Handler与sleep

2、Handler与postDelayed

3、Handler与timer

注：Handler的主要作用就是用来处理接收到的信息；用Handler消息传递机制是为了多个线程并发更新UI的同时，保证线程安全；

一、Handler 与 sleep

public class HandlerAndSleep { 
   

    // 1、定义一个Handler类，用于处理接受到的Message.
    Handler handler = new Handler(Looper.getMainLooper()) { 
   
        @Override
        public void handleMessage(@NonNull Message msg) { 
   
            super.handleMessage(msg);
            // do something eg.
            Log.d("HandlerAndSleep", "HandlerAndSleep");
        }
    };

    // 2、新建一个实现Runnable接口的线程类
    class MyThread implements Runnable { 
   
        @Override
        public void run() { 
   
            while (true) { 
   
                try { 
   
                    Thread.sleep(10000);
                    Message message = new Message();
                    message.what = 1;
                    handler.sendMessage(message);
                } catch (Exception e) { 
   
                    e.printStackTrace();
                }
            }
        }
    }

    public HandlerAndSleep() { 
   
        //3、在需要启动线程的地方加入下面语句,启动线程后，线程每10s发送一次消息
        new Thread(new MyThread()).start();
    }
}

结果打印如下：

2022-05-30 11:30:42.320 17864-17864/com.yh.study D/HandlerAndSleep: HandlerAndSleep
2022-05-30 11:30:52.324 17864-17864/com.yh.study D/HandlerAndSleep: HandlerAndSleep
2022-05-30 11:31:02.326 17864-17864/com.yh.study D/HandlerAndSleep: HandlerAndSleep
2022-05-30 11:31:12.335 17864-17864/com.yh.study D/HandlerAndSleep: HandlerAndSleep
2022-05-30 11:31:22.338 17864-17864/com.yh.study D/HandlerAndSleep: HandlerAndSleep
2022-05-30 11:31:32.339 17864-17864/com.yh.study D/HandlerAndSleep: HandlerAndSleep
2022-05-30 11:31:42.347 17864-17864/com.yh.study D/HandlerAndSleep: HandlerAndSleep

二、Handler 与 postDelayed

public class HandleAndPostDelayed { 
   

    Handler handler = new Handler(){ 
   
        @Override
        public boolean sendMessageAtTime(@NonNull Message msg, long uptimeMillis) { 
   
            Log.d("HandleAndPostDelayed", "HandleAndPostDelayed");
            return super.sendMessageAtTime(msg, uptimeMillis);
        }
    };

    Runnable runnable = new Runnable() { 
   
        @Override
        public void run() { 
   
            // do something
            handler.postDelayed(this, 2000);
        }
    };

    HandleAndPostDelayed() { 
   
    	// 开启定时器
        handler.postDelayed(runnable, 2000);
		// 停止定时器
// handler.removeCallbacks(runnable);
    }
}

结果打印如下：

2022-05-30 14:32:41.533 24351-24351/com.yh.study D/HandleAndPostDelayed: HandleAndPostDelayed
2022-05-30 14:32:43.534 24351-24351/com.yh.study D/HandleAndPostDelayed: HandleAndPostDelayed
2022-05-30 14:32:45.537 24351-24351/com.yh.study D/HandleAndPostDelayed: HandleAndPostDelayed
2022-05-30 14:32:47.539 24351-24351/com.yh.study D/HandleAndPostDelayed: HandleAndPostDelayed
2022-05-30 14:32:49.546 24351-24351/com.yh.study D/HandleAndPostDelayed: HandleAndPostDelayed
2022-05-30 14:32:51.550 24351-24351/com.yh.study D/HandleAndPostDelayed: HandleAndPostDelayed

三、Handler 与 timer

public class HandlerAndTimer { 
   

    private final Timer timer = new Timer();
    private TimerTask task;
    Handler handler = new Handler() { 
   

        @Override
        public void handleMessage(@NonNull Message msg) { 
   
            // do something
            Log.d("HandlerAndTimer", "HandlerAndTimer");
            super.handleMessage(msg);
        }
    };

    public HandlerAndTimer() { 
   
        task = new TimerTask() { 
   
            @Override
            public void run() { 
   
                Message message = new Message();
                message.what = 1;
                handler.sendMessage(message);
            }
        };
        //启动定时器 参数对应为 TimerTask 延迟时间 间隔时间
        timer.schedule(task, 2000, 2000);
    }
}

结果打印如下：

2022-05-30 14:43:40.922 25052-25052/com.yh.study D/HandlerAndTimer: HandlerAndTimer
2022-05-30 14:43:42.924 25052-25052/com.yh.study D/HandlerAndTimer: HandlerAndTimer
2022-05-30 14:43:44.925 25052-25052/com.yh.study D/HandlerAndTimer: HandlerAndTimer
2022-05-30 14:43:46.926 25052-25052/com.yh.study D/HandlerAndTimer: HandlerAndTimer
2022-05-30 14:43:48.927 25052-25052/com.yh.study D/HandlerAndTimer: HandlerAndTimer

在Android上常用的定时器有两种，一种是Java.util.Timer，一种就是系统的AlarmService。

public class MainActivity extends AppCompatActivity { 
   

    Handler handler = new Handler() { 
   
        @Override
        public void handleMessage(@NonNull Message msg) { 
   
            tCount++;
            timerTV.setText(tCount+"");
            super.handleMessage(msg);
        }
    };

    Timer timer = new Timer();
    int tCount = 0;
    int sCount = 0;
    TextView timerTV;
    TextView serviceTV;

    String ALARM_RECEIVER_ACTION = "com.yh.study.AlarmReceiver";
    @Override
    protected void onCreate(Bundle savedInstanceState) { 
   
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        timerTV = findViewById(R.id.timer_tv);
        serviceTV = findViewById(R.id.service_tv);

        timer.schedule(new TimerTask() { 
   
            @Override
            public void run() { 
   
                handler.sendEmptyMessage(0);
            }
        }, 2*1000, 5*1000);

        AlarmReceiver alarmReceiver = new AlarmReceiver(new Handler() { 
   
            @Override
            public void handleMessage(@NonNull Message msg) { 
   
                sCount++;
                serviceTV.setText(sCount+"");
                super.handleMessage(msg);
            }
        });
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(ALARM_RECEIVER_ACTION);
        registerReceiver(alarmReceiver, intentFilter);

        Intent intent = new Intent(ALARM_RECEIVER_ACTION);
        PendingIntent pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0, intent, 0);
//
        AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
        alarmManager.setExactAndAllowWhileIdle(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime(),
                pendingIntent);
    }
}

public class AlarmReceiver extends BroadcastReceiver { 
   

    Handler handler;
    AlarmReceiver(Handler handler) { 
   
        this.handler = handler;
    }

    @Override
    public void onReceive(Context context, Intent intent) { 
   
        Log.d("onReceive", "onReceive");
        handler.sendEmptyMessage(0);
        Intent serviceIntent = new Intent(context, MyService.class);
        context.startService(serviceIntent);
    }
}

public class MyService extends IntentService { 
   
    public MyService() { 
   
        super("MyService");
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) { 
   
        AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);

        Intent alarmIntent = new Intent("com.yh.study.AlarmReceiver");
        PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, alarmIntent, 0);
        alarmManager.setExactAndAllowWhileIdle(AlarmManager.RTC_WAKEUP, System.currentTimeMillis()+5*1000,
                pendingIntent);
    }
}

以下结论来源其他博主（小子在验证过程中，连接usb情况正常，拔掉usb后与结论不符，可能是小子哪里写的有问题）

在Timer中，当连接USB线进行调试时，会发现一切工作正常，每5秒更新一次界面，即使是按下电源键，仍然会5秒触发一次。当拔掉USB线，按下电源键关闭屏幕后，过一段时间再打开，发现定时器明显没有继续计数，停留在了关闭电源键时的数字。
在AlarmService中，拔掉USB线，按下电源键，过一点时间再次打开屏幕，发现定时器一直在计数。

测试机型小米8,上timer，下AlarmService