How should I deal with persisting an Android WebView if my activity gets destroyed while showing another one?

Question

Hi,

I'm building an Android application that's based around an enhanced WebView (based on PhoneGap). I've enhanced the WebView so that from JavaScript running inside you can invoke the native contact picker to choose a phone number (which may be supplied by Facebook for example).

The problem I have is that the native contact picker runs in an activity in another process and the Android docs say that while another activity is open my activity may get destroyed due to memory constraints. I haven't actually seen this happen in my application but if it did then I'm guessing my WebView's state would be destroyed and the code that was waiting for the picked contact would be terminated.

It seems a bit crazy that the activity requesting a contact could be destroyed while the contact picker is open. Does anyone know if that does indeed happen? Is there a way to persist the state of the WebView if it does?

Thanks,

-Shaun

Answer 1

The long and detailed answer is a bit complicated, but essentially it comes down to a few points:

• If the Android OS has to go cleaning up Activities or Services, it knows how to prioritise which ones should go first. It does this based on whether they're currently in the foreground (last to go), in the middle of executing code, waiting for a result, or simply sitting inactive in the background (first to go). You can be reasonably certain that if your WebView Activity launched the contact picker using the startActivityForResult, it won't be killed
• There's a whole system for saving data if an activity is killed, such as the onPause method (which are triggered as soon as your activity leaves the foreground), the onSaveInstanceState method which is called when your activity is about to die. Read up on those to get more information, and the configurationChanged method when the screen orientation changes. If you haven't at least skim read the Activity Lifecycle document on the developers page, you must do that.
• Lastly, I'm sure this question has been addressed many times, but with slightly varying wording or situations. Have a look around, see what else you can find.

Answer 2

Does anyone know if that does indeed happen?

You're looking at the problem too simply.

You have a WebView. You open the contacts application. While the user is in the contacts application, a phone call comes in. While on the phone call (using a Bluetooth headset), a text message comes in, so the user opens that up from its Notification. While still on the phone call and texting away, a text comes in with a link, so she taps it and brings up the Browser application.

By this time, your activity is surely destroyed, except on maybe some of the most recent phones that have a fair bit of RAM.

Now, is that common? No. However, this also has nothing to do with the contacts application -- if the user presses HOME, at some point in the future, your activity may be destroyed to free up RAM as well.

Is there a way to persist the state of the WebView if it does?

That depends on what you consider "the state of the WebView" to be. This really is PhoneGap's job, if you are making a PhoneGap-based app. So, you might consider asking them.

There is no way to persist the DOM. There are trivial ways to persist the URL (see onSaveInstanceState()). And there may be stuff in between that you consider part of "the state of the WebView" that may or may not be possible to save.