CODEWITHSUNDEEP
androidobserver-pattern
jwir3
jwir3

Reputation: 6219

onStartListener available for an activity

I have a series of activities, one of which is called UserActivity. What I'd like to do is have an object ListenerObject, that listens specifically for when UserActivity starts or stops. That is, I want UserActivity.onStart() to call ListenerObject.onActivityStart() (or some method named similarly).

I know that I can create an observer pattern set of classes to do this, but I'm wondering if there already exists such a framework within the Android API, and, more importantly, an accepted set of use patterns.

Upvotes: 1

Views: 63

Answers (3)

FunkTheMonk
FunkTheMonk

Reputation: 10938

Depends on the required life cycle of the ListenerObject. Seems like you want it to be around when the UserActivity isn't, but what about when you have none of your Activities on screen?

You could start a Service and then bind / unbind to it in your UserActivity's onStart / onStop. The service would likely stay alive whilst your app was in the background.

You could (un)bind to a service in all your Activities' onStart/Stop and provide an IBinder interface which asks would allow the service to ask the Activity if it is the UserAnctivity. The service would live whilst you navigate the app, but die once you put it in the background or go to another activity that doesn't bind to it (probably not what you want if you're doing something with G+ authentication / in app purchases etc).

You could (like others suggest) create a singleton, which won't die until the Application does, but won't keep it alive either.

You could have an Event Bus where the Listener subscribes to a known event published by the UserActivity.

shrug just some ideas

Upvotes: 0

Steve M
Steve M

Reputation: 9794

If ListenerObject makes sense as a static singleton you can just call the method on it during onStart() and onStop():

MySingleton.getSharedInstance().onActivityStart();

which would save you some overhead of the other valid methods mentioned.

The Android devs mention static singletons in the context of lazy creation for speed and reduced memory usage quite a bit it seems so it seems like an accepted pattern.

Upvotes: 0

Nathaniel D. Waggoner
Nathaniel D. Waggoner

Reputation: 2886

You could do this through Broadcasts:

http://developer.android.com/reference/android/content/BroadcastReceiver.html

http://developer.android.com/guide/components/intents-filters.html

In a few ways...

1) Have both activities receive and start from the same intent.

2) have activity 1 launch a broadcast to activity 2.

Upvotes: 1

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