iPhone - fast-app switching and iOS 4

I'm trying to get the following functionality in my iPhone app:

• When backgrounded, stays running (doesn't have to do any background work)
• When resumed, app picks up where it was left off

I'm mainly wanting the same screen on my app still up, as there are several UINavigationControllers within a UITabBarController.

I have done all of the following:

• Made sure I'm compiling with 4.1 SDK
• Set UIApplicationExitsOnSuspend to false
• Handle DidEnterBackground and WillEnterForeground in my AppDelegate
• Call BeginBackgroundTask in DidEnterBackground, to attempt to keep my app open

I'm using MonoTouch, bu开发者_开发问答t that it probably beside the point. I can take answers in Obj-C, for sure.

I've tested my app on a jailbroken phone with Backgrounder, and I see the "app in background" badge disappear immediately after pushing the home button. I also tried setting UIBackgroundModes in my Info.plist, but to no avail.

Is there anything I'm missing?

Or is this something I would have to implement on my own to resume the previous state of my app? Everywhere I've read talks like it should just work automatically.

If you don't want to be doing work in background, don't call beginBackgroundTask. That call is for situations where you want to do some kind of work in the background. And if you don't finish that work fast enough, iOS will terminate your app.

When I upgraded to iOS 4.x, my MT application started exhibiting this behavior without me having to do anything. iOS should take care of it for you.

I finally got in touch with someone on MonoTouch's irc.

In MonoDevelop there is an option to make a dual iPad/iPhone project, which I used. This is causing my app to behave as if it's running with the 3.2 SDK when deployed to the device.

I think my solution is to install the iOS 4.2 SDK that just came out, since this ads the new multi-tasking feature on iPad.

Not only do you need to support going into the background, you also need to support cases where your app has been terminated. In your app’s initialization code, you should resume the state that it was in. For instance, when you push a view controller, use NSUserDefaults to store a value for the currently-displayed screen, and then when you start read that value and display the associated screen.