state restoration in iOS

Question

I am storing my application screen, so that when the application gets opened it will show the screen that was stored. The application is navigation based.

I have assigned the Restoration Ids to my two view controllers in main story board. The first controller is the root view controller of the navigation controller. I have also assigned Restoration Id to the navigation controller. Now the problem is when I run the application I am getting the following warning:

Unable to create restoration in progress marker file.

Not sure what else need to be done.

Answer 1

I had the same warning before and fixed it by doing the followings.

I was using storyboard. My storyboard only included a navigation view controller and a view controller (which was the root view controller of that navigation view controller). In my case, it was caused by either of the two reasons:

The application was not set up correctly for state preservation The followings need to be set:

1. In app delegate, override application:willFinishLaunching. One can simply return YES in that method.

2. For every view controllers and views (including the navigation view controllers and tab view controllers), set a restore ID

3. In app delegate, opt-in by overriding shouldSaveApplicationState and shouldRestoreApplicationState

If this warning still occurred, you could check how you run your app in Xcode. I ran my app in Xcode simulator and had to follow a specific sequence to trigger state preservation.

• launch the app in Xcode simulator
• In Xcode simulator, click the "Home" button to put the app into the background. The encodeRestorableStateWithCoder method of the view controller should be called
• go back to Xcode, click the "stop" button to terminate the simulation
• In Xcode simulator, double click the "Home" button and then remove the app from the app switcher and
• go back to Xcode, run the app again.

That warning should not appear. When I used other sequences, I saw that warning appearing. When I debugged my app on my device using Xcode, I followed the same sequence and did not see the warning.

I think that warning indicated that because Xcode could not terminate the app correctly, the state restoration file was not correctly saved onto the disk.