Why UIAlertView prevents my modal view controller from being displayed? - objective-c

Question

Let's say that when the user presses a button a message needs to be shown and then a modal view controller is displayed.
I would write something like that :
- (void)pickImageButtonPressed:(id)button {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Alert"
message:#"Some alert"
delegate:nil
cancelButtonTitle:#"OK"
otherButtonTitles:nil];
[alert show];
[alert release];
UIImagePickerController *picker = [[UIImagePickerController alloc] init];
picker.delegate = self;
picker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
[[UIApplication sharedApplication].keyWindow.rootViewController
presentModalViewController:picker animated:YES];
[picker release];
}
With this code, the modal view controller is simply not displayed !
However, if I switch the two blocks of code (show modal first, then show the alert), the view controller is displayed modally and the alert shows up above it, exactly as I want.
My question is: why the alert prevents the modal view controller from being displayed ?
Please note that I do not want to wait for alert to be dismissed before calling presentModalViewController.
Update :
I figured out that my production code was a bit more complicated than what I first put. I updated the example code and then finally found a simple example to reproduce the problem.
Note that in my production code, the popup is displayed from a place where I don't have any reference to a view controller, that's why I use [UIApplication sharedApplication].keyWindow.rootViewController instead of a direct reference to a view controller

Answer 1

I finally found the answer. The issue really was on this line:
[[UIApplication sharedApplication].keyWindow.rootViewController
presentModalViewController:picker animated:YES];
When an alert is displayed, [UIApplication sharedApplication].keyWindow.rootViewController is nil !. That's why the picker was never displayed. And that's why it worked when I switched the two blocks.
Now I need to find a way to get the most relevant view controller to present the picker modally...