1小时后活动被破坏

Question

I'm new to Android development. I'v developed an android application which needs to store the connection/data even after 1 hour. Currently I have all the data and the connections(chromecast mediaplayer) in a singleton class. But, when the user puts the app into the background for about an hour, the activity is destroyed so the connections,data etc are lost causing my app to crash when re-launched.

I've read up on the android services, Can I use these services to hold the singletons so even when the activities are destroyed I can have data binded back to the views when re-launched?

Or is there a way to make sure that the activities are not destroyed when android decides to do a cleanup? Please advise

Thanks.

Answer 1

I think you might misunderstand what an Android application is.

Your application is a bunch of components that run in a single Linux process. Components come and go, within that process. You have absolutely no control over the lifecycle of the process itself.

The answer to part of your question is that "yes" a Service will stick around after an invisible activity is destroyed.

When an Activity becomes invisible, it gets destroyed. If your process is not doing anything else, then the process is likely to be killed too.

If your process is also running a Service, it is less likely that it will be killed. It is just less likely, though. The process will eventually get killed. When it does, your singletons will be gone. There is nothing you can do to prevent that. So the answer to the second part of your question is "no". You cannot depend on singletons in your service to be around when the process is relaunched

You might look into using the Application object. Its lifecycle is roughly the same as that of your process. It will not live forever but it will be around whenever any other component of your application is around (except ContentProviders).

Answer 2

It sounds like you want to keep connectivity to a chromecast device around when your application is in the background. Obviously services can be helpful but I have a few comments that may come handy:

• Services can be killed by system but based on how you have set them up (eg the return value of onStartCommand()), they can be restarted by the system. When that happens, you cannot expect that your dynamic data is still there (for example your singleton). You need to include logic to recreate what you need again (for example, rebuild your singleton)

• Phone can go to sleep when left for a little while (or user can lock his/her phone), so when phone goes to sleep, wifi may drop after a little while, based on the phone settings and the build on your phone; some do this more aggressively and some not (even if you hold a lock, it can still happen). The point is that you have to assume that it may happen. Even if you have a service, your Cast connection will go down due to wifi loss, so the proper way to handle things is not to try to keep the connection up all the time (since you can't) but is to have logic to re-establish connection when circumstances is right. In order to do that, you need to preserve enough information to be able to bring things to the state that they were. Your logic should also be intelligent enough not to reconnect if it shouldn't.

Answer 3

Android OS can destroy any activity , when it is low at resources it destroys any activities to make more space for other apps. But you can use background service to hold your singleton

You can use this link to create your background service