Save the state of UIImageView using restorationIdentifier in iOS6 - ios

Question

I read in the documentation that the #property(nonatomic, copy) NSString *restorationIdentifier is capable of preserving the state of an UIImageView properties such as position, angle, etc. I tried adding the methods
-(BOOL)application:(UIApplication *)application shouldRestoreApplicationState:(NSCoder *)coder
{
return YES;
}
-(BOOL)application:(UIApplication *)application shouldSaveApplicationState:(NSCoder *)coder
{
return YES;
}
to the view controller. I have set the restoration ID of the view controller as #"myFirstViewController in the IB.
I have added the following methods to the view controller as well.
-(void)encodeRestorableStateWithCoder:(NSCoder *)coder
{
[coder encodeObject:_myImageView.image forKey:#"UnsavedImage"];
[super decodeRestorableStateWithCoder:coder];
}
-(void)decodeRestorableStateWithCoder:(NSCoder *)coder
{
_myImageView.image = [coder decodeObjectForKey:#"UnsavedImage"];
[super encodeRestorableStateWithCoder:coder];
}
Am i supposed to add the first two methods in the appDelegate or the view controller?
The UIImageView is not getting preserved. What is wrong here?

Answer 1

To make the state preservation and restoration work there are two steps that are always required:
The App delegate must opt-in
Each view controller or view to be
preserved/restored must have a restoration identifier assigned.
You should also implement encodeRestorableStateWithCoder: and decodeRestorableStateWithCoder: for views and view controllers that require state to be saved and restored.
Add the following methods to the view controller of your UIImageView.
-(void)encodeRestorableStateWithCoder:(NSCoder *)coder
{
[coder encodeObject:UIImagePNGRepresentation(_imageView.image)
forKey:#"YourImageKey"];
[super decodeRestorableStateWithCoder:coder];
}
-(void)decodeRestorableStateWithCoder:(NSCoder *)coder
{
_imageView.image = [UIImage imageWithData:[coder decodeObjectForKey:#"YourImageKey"]];
[super encodeRestorableStateWithCoder:coder];
}
State preservation and restoration is an optional feature so you need to have the application delegate opt-in by implementing two methods:
- (BOOL)application:(UIApplication *)application shouldSaveApplicationState:(NSCoder *)coder
{
return YES;
}
- (BOOL)application:(UIApplication *)application shouldRestoreApplicationState:(NSCoder *)coder
{
return YES;
}
Useful article about state preservation:
http://useyourloaf.com/blog/2013/05/21/state-preservation-and-restoration.html