Android警报管理器和待定意图

Question

I am looking at the page for Alarm Manager in Android and see that we can use Pending Intent to trigger a component after a certain time using this feature.

I can the see utility of this feature, but am interested in knowing why was this feature introduced. Can't an application count time itself and trigger an Intent after a certain amount of time ? What are the unique advantages of using Pending Intent with Alarm Manager to achieve the same goal ?

Answer 1

Activities are volatile in Android. Android can decide to destroy the application at any time or pause it. If a long running activity is paused or destroyed, how can it know the current time and trigger the Intent? Alarm Manager sets the alarm in the system and at that time, or roughly at the specified time, depending on the number of alarms set in the system the alarm is triggered, and you can use it to trigger an Intent.

Edit: an application can have a service. The service is part of the application and runs on the application thread. You can create an handler so it triggers some code from the current time to a determined number of seconds, and this is all fine, since the service won't continually run and take all the focus in the main thread. A service is something that runs its code and then finishes. It doesn't stay there waiting on some line. It runs on the main thread so it can cause an ANR on the application if there is code in the service always running. Counting time is not something that should be done, like a while loop in the service, because it takes all the processing power and freezes the application. This is why an Alarm is useful, Android triggers it on that moment, it is not something that is processing in your application. Of course you can create a service in another thread, but unless counting time like a clock is really necessary, and I don't see why would it be, Alarm is better for this.