Android: How to use AlarmManager Android: 如何使用 AlarmManager

"Some sample code" is not that easy when it comes to AlarmManager.

Here is a snippet showing the setup of AlarmManager:

AlarmManager mgr=(AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
Intent i=new Intent(context, OnAlarmReceiver.class);
PendingIntent pi=PendingIntent.getBroadcast(context, 0, i, 0);


mgr.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime(), PERIOD, pi);

In this example, I am using setRepeating(). If you want a one-shot alarm, you would just use set(). Be sure to give the time for the alarm to start in the same time base as you use in the initial parameter to set(). In my example above, I am using AlarmManager.ELAPSED_REALTIME_WAKEUP, so my time base is SystemClock.elapsedRealtime().

Here is a larger sample project showing this technique.

There are some good examples in the android sample code

.\android-sdk\samples\android-10\ApiDemos\src\com\example\android\apis\app

The ones to check out are:

• AlarmController.java
• OneShotAlarm.java

First of, you need a receiver, something that can listen to your alarm when it is triggered. Add the following to your AndroidManifest.xml file

<receiver android:name=".MyAlarmReceiver" />

Then, create the following class

public class MyAlarmReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
Toast.makeText(context, "Alarm went off", Toast.LENGTH_SHORT).show();
}
}

Then, to trigger an alarm, use the following (for instance in your main activity):

AlarmManager alarmMgr = (AlarmManager)getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(this, MyAlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0, intent, 0);
Calendar time = Calendar.getInstance();
time.setTimeInMillis(System.currentTimeMillis());
time.add(Calendar.SECOND, 30);
alarmMgr.set(AlarmManager.RTC_WAKEUP, time.getTimeInMillis(), pendingIntent);

.

Or, better yet, make a class that handles it all and use it like this

Bundle bundle = new Bundle();
// add extras here..
MyAlarm alarm = new MyAlarm(this, bundle, 30);

this way, you have it all in one place (don't forget to edit the AndroidManifest.xml)

public class MyAlarm extends BroadcastReceiver {
private final String REMINDER_BUNDLE = "MyReminderBundle";


// this constructor is called by the alarm manager.
public MyAlarm(){ }


// you can use this constructor to create the alarm.
//  Just pass in the main activity as the context,
//  any extras you'd like to get later when triggered
//  and the timeout
public MyAlarm(Context context, Bundle extras, int timeoutInSeconds){
AlarmManager alarmMgr =
(AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(context, MyAlarm.class);
intent.putExtra(REMINDER_BUNDLE, extras);
PendingIntent pendingIntent =
PendingIntent.getBroadcast(context, 0, intent,
PendingIntent.FLAG_UPDATE_CURRENT);
Calendar time = Calendar.getInstance();
time.setTimeInMillis(System.currentTimeMillis());
time.add(Calendar.SECOND, timeoutInSeconds);
alarmMgr.set(AlarmManager.RTC_WAKEUP, time.getTimeInMillis(),
pendingIntent);
}


@Override
public void onReceive(Context context, Intent intent) {
// here you can get the extras you passed in when creating the alarm
//intent.getBundleExtra(REMINDER_BUNDLE));


Toast.makeText(context, "Alarm went off", Toast.LENGTH_SHORT).show();
}
}

Some sample code when you want to call a service from the Alarmmanager:

PendingIntent pi;
AlarmManager mgr;
mgr = (AlarmManager)ctx.getSystemService(Context.ALARM_SERVICE);
Intent i = new Intent(DataCollectionActivity.this, HUJIDataCollectionService.class);
pi = PendingIntent.getService(DataCollectionActivity.this, 0, i, 0);
mgr.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime() , 1000, pi);

You dont have to ask userpermissions.

What you need to do is first create the intent you need to schedule. Then obtain the pendingIntent of that intent. You can schedule activities, services and broadcasts. To schedule an activity e.g MyActivity:

  Intent i = new Intent(getApplicationContext(), MyActivity.class);
PendingIntent pi = PendingIntent.getActivity(getApplicationContext(),3333,i,
PendingIntent.FLAG_CANCEL_CURRENT);

Give this pendingIntent to alarmManager:

  //getting current time and add 5 seconds in it
Calendar cal = Calendar.getInstance();
cal.add(Calendar.SECOND, 5);
//registering our pending intent with alarmmanager
AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);
am.set(AlarmManager.RTC_WAKEUP,cal.getTimeInMillis(), pi);

Now MyActivity will be launched after 5 seconds of the application launch, no matter you stop your application or device went in sleep state (due to RTC_WAKEUP option). You can read complete example code Scheduling activities, services and broadcasts #Android

I wanted to comment but <50 rep, so here goes. Friendly reminder that if you're running on 5.1 or above and you use an interval of less than a minute, this happens:

Suspiciously short interval 5000 millis; expanding to 60 seconds

See here.

An AlarmManager is used to trigger some code at a specific time.

To start an Alarm Manager you need to first get the instance from the System. Then pass the PendingIntent which would get executed at a future time that you specify

AlarmManager manager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);


Intent alarmIntent = new Intent(context, MyAlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, alarmIntent, 0);
int interval = 8000; //repeat interval
manager.setInexactRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), interval, pendingIntent);

You need to be careful while using the Alarm Manager. Normally, an alarm manager cannot repeat before a minute. Also in low power mode, the duration can increase to up to 15 minutes.