Using an instance of a UIViewController, is there any way I can find the UIPopoverController being used to present it? I would also want to find the UIViewController that displayed the UIPopoverController in the first place.
I would normally use a delegate or other sort of notification to send a signal from the displayed view controller to the displaying one, but in this case I'm trying to create a reusable custom segue that dismisses the popover and then moves on to another view in the main view.
Both are used for different purpose. A UIViewController class manages a ViewContoller which is responsible for actions that happen within that View controller. This class is aware of actions that happen on view controller, like ViewDidLoad, ViewWillApper, ViewDidAppear, ViewWillDisapper, ViewDidDisapper.
A UIViewController is an object which manages the view hierarchy of the UIKit application. The UIViewController defines the shared behavior and properties for all types of ViewController that are used in the iOS application. The UIViewController class inherits the UIResponder class.
You would think that this would be simple (the UIViewController
even has a private _popoverController
property!), but it is not.
The general answer is that you have to save a reference to the UIPopoverController
in the UIViewController
that it is presenting, at the time the UIViewController
is created.
If you are creating the UIPopoverController
programmatically, then that's the time to store the reference in your UIViewController
subclass.
If you are using Storyboards and Segues, you can get the UIPopoverController
out of the segue in the prepareForSegue
method:
UIPopoverController* popover = [(UIStoryboardPopoverSegue*)segue popoverController];
Of course, be sure that your segue really is a UIStoryboardPopoverSegue!
My recommendation is to leverage a combination of your own custom property and the private APIs in UIKit. To avoid app store rejection, any private APIs should compile out for release builds, and should be used only to check against your implementation.
First let's build the custom property into a category on UIViewController
. This allows some perks in the implementation, and it doesn't require you to go back and derive every class from some custom view controller subclass.
// UIViewController+isPresentedInPopover.h
#import <UIKit/UIKit.h>
@interface UIViewController (isPresentedInPopover)
@property (assign, nonatomic, getter = isPresentedInPopover) BOOL presentedInPopover;
@end
Now for the implementation - we'll be using the Objective C runtime's associated object API to provide the storage for this property. Note that a selector is a nice choice for the unique key used to store the object, as it's automatically uniqued by the compiler and highly unlikely to be used by any other client for this purpose.
// UIViewController+isPresentedInPopover.m
#import "UIViewController+isPresentedInPopover.h"
#import <objc/runtime.h>
@implementation UIViewController (isPresentedInPopover)
- (void)setPresentedInPopover:(BOOL)presentedInPopover
{
objc_setAssociatedObject(self,
@selector(isPresentedInPopover),
[NSNumber numberWithBool:presentedInPopover],
OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (BOOL)isPresentedInPopover
{
NSNumber *wrappedBool = objc_getAssociatedObject(self, @selector(isPresentedInPopover));
BOOL userValue = [wrappedBool boolValue];
return userValue ?: [[self parentViewController] isPresentedInPopover];
}
@end
So there's a convenient side effect of using this as a category - you can call up to the parentViewController
and see if that is contained in a popover as well. This way you can set the property on, say, a UINavigationController
and all of its child view controllers will respond correctly to isPresentedInPopover
. To accomplish this with subclasses, you'd be either trying to set this on every new child view controller, or subclassing navigation controllers, or other horrific things.
There is still more that the Objective C Runtime has to offer for this particular problem, and we can use them to jump into Apple's private implementation details and check your own app against it. For release builds, this extra code will compile out, so no need to worry about the all-seeing eye of Sauron Apple when submitting to the store.
You can see from UIViewController.h
that there is an ivar defined as UIPopoverController* _popoverController
with @package
scope. Luckily this is only enforced by the compiler. Nothing is sacred as far as the runtime is concerned, and it's pretty easy to access that ivar from anywhere. We'll add a debug-only runtime check on each access of the property to make sure we're consistent.
// UIViewController+isPresentedInPopover.m
#import "UIViewController+isPresentedInPopover.h"
#import <objc/runtime.h>
@implementation UIViewController (isPresentedInPopover)
- (void)setPresentedInPopover:(BOOL)presentedInPopover
{
objc_setAssociatedObject(self,
@selector(isPresentedInPopover),
[NSNumber numberWithBool:presentedInPopover],
OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
- (BOOL)isPresentedInPopover
{
NSNumber *wrappedBool = objc_getAssociatedObject(self, @selector(isPresentedInPopover));
BOOL userValue = [wrappedBool boolValue];
#if DEBUG
Ivar privatePopoverIvar = class_getInstanceVariable([UIViewController class], "_popoverController");
UIPopoverController *popover = object_getIvar(self, privatePopoverIvar);
BOOL privateAPIValue = popover != nil;
if (userValue != privateAPIValue) {
[NSException raise:NSInternalInconsistencyException format:
@"-[%@ %@] "
"returning %@ "
"while private UIViewController API suggests %@. "
"Did you forget to set 'presentedInPopover'?",
NSStringFromClass([self class]), NSStringFromSelector(_cmd),
userValue ? @"YES" : @"NO",
privateAPIValue ? @"YES" : @"NO"];
}
#endif
return userValue ?: [[self parentViewController] isPresentedInPopover];
}
@end
When using the property incorrectly, you'll get a message like this on the console:
2012-09-18 14:28:30.375 MyApp[41551:c07] * Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Consistency error in -[UINavigationController isPresentedInPopover]: returning NO while private UIViewController API suggests YES. Did you forget to set 'presentedInPopover'?'
...but when compiling with the DEBUG flag off or set to 0, it compiles down to the exact same code as before.
Maybe you're doing Ad-Hoc/Enterprise/personal builds, or you're sufficiently bold to see just what Apple thinks about this one for the App Store. Either way, here's an implementation that just works using the current runtime and UIViewController
- no setting properties needed!
// UIViewController+isPresentedInPopover.h
#import <UIKit/UIKit.h>
@interface UIViewController (isPresentedInPopover)
@property (readonly, assign, nonatomic, getter = isPresentedInPopover) BOOL presentedInPopover;
@end
// UIViewController+isPresentedInPopover.m
#import "UIViewController+isPresentedInPopover.h"
#import <objc/runtime.h>
@implementation UIViewController (isPresentedInPopover)
- (BOOL)isPresentedInPopover
{
Ivar privatePopoverIvar = class_getInstanceVariable([UIViewController class], "_popoverController");
UIPopoverController *popover = object_getIvar(self, privatePopoverIvar);
BOOL privateAPIValue = popover != nil;
return privateAPIValue ?: [[self parentViewController] isPresentedInPopover];
}
@end
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