Override UIViewController.view with specific type - ios

Question

Let's consider an application with highly customized or complex views.
We'll have a specific kind of view-controller sending methods to a specific kind of UIView, where the UIView is itself composed of a number of other views.
The view should have a rich, domain-specific interface, allowing the controller to act is a thin "glue" layer between it and a similarly rich model.
So we override our controller's view property as follows:
#interface PlaybackViewController : UIViewController<StageLayoutDelegate, ControlPanelDelegate>
{
NSMutableArray* _sections;
LightingMode _lightingMode;
}
#property (nonatomic, strong) PlaybackView* view; // <------ Specific type of view
#pragma mark - injected
#property (nonatomic, strong) id<OscClient> oscClient;
#property (nonatomic, strong) AbstractStageLayoutView* stageLayoutView;
#end
Ovverriding makes sense over defining another accessor, and I can just send messages to the specific type of UIView without having to cast.
Problem: The only problem is that it results in a compiler warning:
property type 'PlaybackView *' is incompatible with type 'UIView *' inherited from 'UIViewController'
. . and I like to build code that doesn't have any warnings. This way a valid warning doesn't get missed by being buried amongst other warnings.
Question:
Is there a way to suppress this particular warning?
Why is this part of the default settings, when most modern OO languages will happily allow overriding a property or method in a sub-class so that it returns a more specific sub-class of the type declared in the super-class?

Answer 1

The problem here is not not the override of the property, its using a forward declaration of the class type.
So this...
#class PlaybackView;
#interface PlaybackViewController : UIViewController
#property (nonatomic, strong) PlaybackView* view;
#end
will give you the mentioned warning because the compiler cannot know the inheritance hierarchy of PlaybackView. UIViewController has a contract to provide a UIView from its view property
Its telling you that it thinks PlaybackView is not a UIView
The simple solution here is to use a #import instead to give the compiler full knowledge of PlaybackView...
#import "PlaybackView.h"
#interface PlaybackViewController : UIViewController
#property (nonatomic, strong) PlaybackView* view;
#end
alternatively (but really bad form as the PCH is an optimising feature and shouldn't manage dependancies ) is to add #import "PlaybackView.h" to your projects PCH

Answer 2

As suggested in another answer using #import instead of #class will clear the warning but it is advised to import as little as possible in the header, so I would recommend leaving the view unchanged and having an additional PlaybackView * playbackView:
It is perfectly fine to have both view and playbackView pointing to the same view.
Classes that need to have knowledge of your specialized view have to import your controllers header, so they could just use playbackView in the first place.
More important, if you want to embed your specialized view as a subview in the future (which happens often like adding a UIScrollView superview), you won't have to refactor other code and classes!
It's plain cleaner.

Answer 3

I do not think override UIViewControllers view property is a good way .
I think it is better to do like this :
#interface PlaybackViewController : UIViewController<StageLayoutDelegate, ControlPanelDelegate>
{
NSMutableArray* _sections;
LightingMode _lightingMode;
}
//#property (nonatomic, strong) PlaybackView* view; //you do not need this property
#pragma mark - injected
#property (nonatomic, strong) id<OscClient> oscClient;
#property (nonatomic, strong) AbstractStageLayoutView* stageLayoutView;
#end
and in the .m file .
- (void)loadView
{
PlaybackView *mainView = [[PlaybackView alloc] initWithFrame:[UIScreen mainScreen].applicationFrame];
// set the mainView
self.view = mainView;
}
and you can use your PlaybackView like this .
((PlaybackView *)(self.view)).oscClient
or
((PlaybackView *)(xxxViewControler.view)).oscClient

Answer 4

Perhaps you could declare another method that provides the cast for you, in a sense.
#implementation PlaybackViewController
- (void)viewDidLoad {
[super viewDidLoad];
// use view_ property instead of view
self.view_.foo = 1;
}
- (void)loadView {
CGRect frame = [UIScreen mainScreen].applicationFrame;
self.view = [[PlaybackView alloc] initWithFrame:frame];
}
- (PlaybackView *)view_ {
return (PlaybackView *)self.view;
}
Not exactly the cleanest approach, but it does avoid the cast on self.view (by not using self.view, though)

Answer 5

[UPDATE]
Finally I've probably found a solution that suit the problem:
This is a quick and dirty just to suppress the warning, try to wrap your code between these lines
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
//YOUR CODE
#pragma clang diagnostic pop
or -Wall
To see more about compiler warning suppression Clang Manual
[OLD ANSWER]
I'd like to give my 2 cents.
If I understood well you are trying to create a sort of Abstract factory, that gives you a specialized version of a view based on the view controller funcionality. In my opinion storyboards doesn't work well in that kind of design, but I'd like to give you my vision about it.
First I will create an abstract class for your view controller where in the interface you declare all property you need in all your VC sublcasses, such as :
OSClient
AbstractStageLayoutView
PlaybackView as weak
playbackProperty
The PlaybackView class is a class cluster such as NSNumber, you call a factory method on it, that will return an object that could be different from case to case. If you inspect an NSnumber it returns a different object if you create a float or an integer, but they are all subclasses of NSNumber, and NSNumber declares all the property of its subclasses, but it doesn't implement them.
Now what you can do in the -viewDidLoad method of the abstract class is call a method like that
PlaybackView *plbackView = [PlaybackView playbackViewFroProperty:self.playbackProperty];
[self.view addSubview:playbackView];
self.playbackView = plbackView;
The playbackProperty can be valued inside the User defined runtime attibute in the viewcontroller storyboard editor.