Image not being set in method

I have a class with a viewDidLo开发者_开发知识库ad method and an artworkInfo method as follows:

-(void)viewDidLoad {
    mainDelegate = (AppDelegate*)[[UIApplication sharedApplication]delegate];   

    [super viewDidLoad];
}

-(void)artworkInfo:(NSNumber *)pos{
    mainDelegate = (AppDelegate*)[[UIApplication sharedApplication]delegate];   

[self.image setImage:(UIImage *)[[mainDelegate.mapAnnotations objectAtIndex:0]image]];

}

the mainDelegate thing is to gain access to the appDelegate where an array is stored, but anyway, with the "[self.image setImage...]" command where it is, the image on the app does not appear, but when I copy that exact line of code into the viewDidLoad method, it shows up like it should. I know that the artworkInfo method is being called because I debugged it and it goes through, so I can't figure out why the command would not be doing anything it's current method while it will in the viewDidLoad...?

Also, here is where the method is called and this new view is loaded from another class:

infoPage *info = [[infoPage alloc] initWithNibName:@"infoPage" bundle:nil];
    info.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
    [self presentModalViewController:info animated:YES];
    infoPage *myInfoPage = [[infoPage alloc] init];
    [myInfoPage artworkInfo:position];
    [info release];

OH, I see the problem. You're instantiating 2 different infoPage classes.

Change this:

infoPage *info = [[infoPage alloc] initWithNibName:@"infoPage" bundle:nil];
info.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentModalViewController:info animated:YES];
infoPage *myInfoPage = [[infoPage alloc] init];
[myInfoPage artworkInfo:position];
[info release];

to this:

infoPage *info = [[infoPage alloc] initWithNibName:@"infoPage" bundle:nil];
info.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentModalViewController:info animated:YES];
[info artworkInfo:position];
[info release];

Ok detailed answer. In order to understand why this image is not displaying properly you have to first look at how Runloops work in Objective C.

While viewDidLoad is the method that is called when a view is loaded and it is technically also called before a view is displayed and it's view objects initialized. Since presentModalViewController is an animation there is actually some threading going on in the works.

viewDidLoad gets called before the animation is created for the presentModalView. This initializes your objects. However, due to some of the inner workings of UI Kit some processes are loaded off into a thread. When they complete they run callback methods on the main UI thread.

Since presentModalViewController is a non-blocking method your artworkInfo method gets added to the mainRunLoop before the initializer form thread adds its callback methods to the main run loop. The best approach would be to have both a UIImage property of your viewController and a UIImageView.

set the value of UIImage by calling artworkInfo BEFORE the presentModalViewController method.

in your ViewDidLoad go ahead and set the value of your UIImageView

[self.imageView setImage:self.image];

Problem solved.

This seems pretty straight forward.

So you initialize your nib and try to call your method artwork before the nib is fully loaded. <-- This is not working for you.

Then you do additional initialization by overrider viewDidLoad per the doco where the nib is loaded <-- This is working for you

So the answer is, when you call setImage before your nib is loaded, then there is nothing to set the image to. When you call setImage in viewDidLoad your nib is loaded and then things should work just fine.

I hope this explains it a bit.