Android : AlarmManager

Android应用中使用Alarm事件，其功能和Java.util.Timer ,TimerTask类似。但Alarm可以即使当前应用退出后也可以做到Schedule一个任务在指定的时刻执行。

AlarmManager 用于管理Alarm事件，支持单次执行或重复执行。 和大都数Android服务一样，AlarmManager也是通过getSystemService来获取服务对象：

AlarmManager am = (AlarmManager)getSystemService(ALARM_SERVICE);  

与TimerTask对应的任务描述类型为PendingIntent，PendingIntent描述了将要执行的Intent，PendingIntent没有提供构造函数，需要通过static 函数getActivity(Context, int, Intent, int), getBroadcast(Context, int, Intent, int), getService(Context, int, Intent, int) 来或得想要执行的Activity，Broadcast，Service描述。

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定时启动 Activity

Intent intent = new Intent(this, MainActivity.class);
intent.setAction(Intent.ACTION_MAIN);
intent.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
// 定时启动窗口（10s后开始，每隔10s启动一次）
alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME,
        SystemClock.elapsedRealtime() + 10000, 10000, pendingIntent);

若需要窗体正在运行时不启动，运行在后台时自动启动，在 AndroidManifest.xml 的 Activity 属性中添加 android:launchMode="singleTask"即可。

<activity android:name=".MainActivity"
    android:launchMode="singleTask">
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

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定时执行Broadcast事件

OneShotAlarm.java

public class OneShotAlarm extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "OneShotAlarm", Toast.LENGTH_SHORT).show();
    }
}

RepeatingAlarm.java

public class RepeatingAlarm extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "RepeatingAlarm", Toast.LENGTH_SHORT).show();
    }
}

AndroidManifest.xml

<receiver android:name=".OneShotAlarm"/>
<receiver android:name=".RepeatingAlarm"/>

MainActivity.java

public class MainActivity extends AppCompatActivity {

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

        Button btnOneShotAlarm = (Button) findViewById(R.id.btn_one_shot_alarm);
        Button btnStartRepeatingAlarm = (Button) findViewById(R.id.btn_start_repeating_alarm);
        Button btnStopRepeatingAlarm = (Button) findViewById(R.id.btn_stop_repeating_alarm);

        // 单次执行，向OneShotAlarm发出一个Broadcast Intent
        btnOneShotAlarm.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, OneShotAlarm.class);
                PendingIntent pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0, intent, 0);

                Calendar calendar = Calendar.getInstance();
                calendar.setTimeInMillis(System.currentTimeMillis());
                calendar.add(Calendar.SECOND, 3);

                AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
                alarmManager.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
            }
        });

        // 重复执行，每5秒向RepeatingAlarm发送一个Broadcast事件
        btnStartRepeatingAlarm.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, RepeatingAlarm.class);
                PendingIntent pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0, intent, 0);

                long firstTime = SystemClock.elapsedRealtime();
                firstTime += 5 * 1000;

                AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
                alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, firstTime, 5*1000, pendingIntent);
            }
        });

        // 取消重复执行
        btnStopRepeatingAlarm.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this, RepeatingAlarm.class);
                PendingIntent pendingIntent = PendingIntent.getBroadcast(MainActivity.this, 0, intent, 0);

                AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
                alarmManager.cancel(pendingIntent);
            }
        });
    }
}

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参考：

• https://developer.android.com/samples/RepeatingAlarm/index.html

• http://blog.youkuaiyun.com/mapdigit/article/details/7644134