// Create a new popover controller that will display the imagePicker imagePickerPopover = [[UIPopoverController alloc]
initWithContentViewController:imagePicker];
[imagePickerPopover setDelegate:self];
// Display the popover controller; sender
// is the camera bar button item
[imagePickerPopover presentPopoverFromBarButtonItem:sender permittedArrowDirections:UIPopoverArrowDirectionAny
animated:YES];
To dismiss a modally-presented view controller, you must send the message dismissViewControllerAnimated:completion: to the view controller that presented it. You’ve done this before with UIImagePickerController – the DetailViewController presented it, and when the image picker told the DetailViewController it was done, the DetailViewController dismissed it.
Now, we have a slightly different situation. When a new item is created, the ItemsViewController presents the DetailViewController modally. The DetailViewController has two buttons on its navigationItem that will dismiss it when tapped: Cancel and Done. There is a problem here: the action messages for these buttons are sent to the DetailViewController, but it is the responsibility of the ItemsViewController to do the dismissing. The DetailViewController needs a way to tell the view controller that presented it, “Hey, I’m done, you can dismiss me now.”
Fortunately, every UIViewController has a presentingViewController property that points to the view controller that presented it. The DetailViewController will grab a pointer to its presentingViewController and send it the message dismissViewControllerAnimated:completion:.
Implement the action method for the Save button in DetailViewController.m.
[[self presentingViewController] dismissViewControllerAnimated:YES completion:nil];
There are two built-in properties for managing the relationship between presenter and presentee. A modally-presented view controller’s presentingViewController will point back to the view controller that presented it, while the presenter will keep a pointer to the presentee in its presentedViewController property
Presentation context
(不是很理解)
参考信息：https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/ModalViewControllers/ModalViewControllers.html
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