If I start a service in my main activity, then exit main and create main again, will a new service instance be put in its place? or will it be the same instance? or will there be two instances?
I need to know because in my service I make a unique id for every time a new service is created.
Whenever you call startService() or startForegroundService() in Android, the framework checks if that Service is already running.
So to answer your question, yes. There will only be a single instance.
However, every time you call startService() or startForegroundService(), the Service's onStartCommand() method will be called. That means, if you have any one-time initialization in your Service that you don't want to be reinitalized, put it in onCreate().
If I start a service in my main activity, then exit main and create
main again, will a new service instance be put in its place?
You have two situations If your service remains running a new instance will not be created but if your service stops (ends its work or system stops it due to low memory or other situations) when you start it again you get a new instance of it.
Related
I have my main activity that creates a service, binds to it and start calling its method. Lets say this Activity is destroyed. The service keeps running (as it should be). Now when the activity starts again, how can I connect to the service again (and not start new one)?
What's the right way of doing it
Thanks
Android services are created as singletons, so the framework will always guarantee that only 1 instance of the service is ever running, even if you call StartService 10 times in a row.
Simply run StartService and then BindService each time. If the service is already started, the StartService will simply not do anything.
I have a doubt that if i start a periodic service using alarm manager and start the service from the onCreate method of an activity. How can i prevent the service from triggering multiple times if that activity is launched again and again.
Assuming that you are creating a Normal Service (and not an IntentService), as per the Android Service documentation, when app invokes startService call, service will be instantiated and started (creating a process for it if needed).
Also, if it is running then it remains running.
So, to put it in simple terms,
Life cycle of "Started" service is independent of the life cycle of
Activity which has started this service. This is true irrespective
weather both are running in same process or different processes
So even though your Activity may be getting created multiple times, and if Service you created earlier is still running, then service object that already exists will be reused.
However, if there is a call to startService() from onCreate() of an Activity, this will invoke each time onStartCommand().
Hence, you need to ensure that you have a appropriate code/logic to handle multiple invocations of onStartCommand()
As far as I understood you must do something in either onCreate/onStart and onStop or onResume and onPaused. By do something I mean, in onCreate create what you need, alarm manager, etc then in onStart you can start the service and in onStop you stop the service or unBind from it, in case you want a foreground service. or in onResume or onStop.
Take a look here:
https://github.com/toaderandrei/live_tracking/blob/master/app/src/main/java/com/ant/track/activities/ServiceConnectActivity.java.
It is a tracking app that is based on MyTracks app from google.
Suppose that Activity A starts Service S and binds to Service S.
What will happen to S when A is destroyed?
How can I recreate another Activity that binds to S? The sample code in http://developer.android.com/guide/components/bound-services.html unbind the service in onStop(). I think if I open the app again, a new process is created for another instance of A and S. But I want the new activity to get data from the old service.
What will happen to S when A is destroyed?
If A is the only Activity bound to S and you didn't start the Service via startService(Intent), S will be destroyed. That's because a Service will be alive till the last bound Activity unbounds from the Service. This is documented here.
How can I recreate another Activity that binds to S?
If A is bound and you switch to Activity B via Intent, the Service will be destroyed and recreated when B binds to it.
If you want the Service to be alive even if no Activity is bound to it, you have to call the Servie with startService(Intent). Now it will be around if you explicitly stop it or system means it's time to destroy it. If you don't want this behavior, persist your data and access it at given time.
I think if I open the app again, a new process is created for another instance of A and S
The process remains the same till the process is killed from the system or if you kill the process, which is not recommanded.
Edit:
Only the bound service lifecycle depends on Activities. If you want a stand alone one use startService(). This way it's independent from Activities and runs in background as long as the process of the App is up or you explicitly stop the Service with stopService() / stopSelf(). You could even have a Service in a own App and use IPC to communicate between Apps. It's all a matter of the use case.
As you can see the configuration of a Service is very flexible and you have to decide which fits best for your App.
If You start service through startService() it will keep remaining after Activity finishes.
If You start service through bindService() it will live until last Activity unbounds from it.
Also if service is already started and you call startService() no new instance of service will be created, but in living service method onStartCommand() will be executed.
Almost same when you bind to living service, methon onBind() will be executed.
I have a service which I know is already running, how does my activity communicate with it without restarting the service.
to elaborate, I have a widget which starts a service, upon click an activity gets loaded, in that scenario the service should still be running.
How do I do something along the lines of:
conditionally checking if the service is alive
accessing methods in the service
Basically, the main thing I do not want to do is run startService(new Intent(...)) within my activity. I don't want to run onStart again within my service.
Ideally I can just add some methods within my service class, and call those within my activity, like I would call any other public method in the project.
I want to start some new threads within my service, and I don't want to make a second service class if I don't have to.
Thanks for the insight
The documentation on startService() might help:
Request that a given application service be started. The Intent can either contain the complete class name of a specific service implementation to start, or an abstract definition through the action and other fields of the kind of service to start. If this service is not already running, it will be instantiated and started (creating a process for it if needed); if it is running then it remains running.
...
Returns
If the service is being started or is already running, the ComponentName of the actual service that was started is returned; else if the service does not exist null is returned.
So if your Service is already running, startService() won't start a new version.
I have a service running in background. I started it from an Activity, but I want to recover an instance of that service from another activity (in the same app) in order to call one method.
Is it possible?
There is only one instance of the service, at most. You cannot have two instances. Hence, just have the second activity bind to the service ("recovery an instance").