Following an example about GLKViewController, I implemented update callback like the following
- (void)update
{
}
But I checked the source, looks like there is no update message defined, why I can use update?
#protocol GLKViewDelegate <NSObject>
#required
/*
Required method for implementing GLKViewDelegate. This draw method variant should be used when not subclassing GLKView.
This method will not be called if the GLKView object has been subclassed and implements -(void)drawRect:(CGRect)rect.
*/
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect;
#end
GLKViewController manages an animation timer that tells your app when to draw (and relatedly, tells you when drawing is about to happen so you can implement per-frame logic for simulations or gameplay or whatever). GLKView manages how to draw—you subclass it or use its delegate to provide rendering code.
If you subclass GLKViewController, you can put per-frame logic in a method whose signature is -(void)update. This method is not listed in the GLKViewController class definition because it's not a method declared or implemented by the class—it's only for subclasses. (This is described in the class overview documentation.)
Alternatively, if you use a stock GLKViewController, you can use your own custom class as its delegate and put per-frame logic in glkViewControllerUpdate:.
Related
I am trying to develop an Cocoa Touch Framework or a dynamic Library.
This Framework should intercept the touch, swipe, pan gestures on views. For starting let us assume that I want to intercept touch event on every control (UIButton, UIView etc. ) and it should be captured in the Framework where I would use that data for further processing.
Could anyone direct me in correct direction about how to target this?
If you want to replace methods in UI classes you can replace methods in base classes (UIView or UIViewController). If you do not want to call super inside a code of your classes. You should swizzle methods inside any of your subclass.
To achieve this, I see two solutions:
1. First, create custom subclass for UIView, UIControl, UIViewController. These subclasses should have swizzled methods and don't call super.
#interface CustomViewBase
#end
#implementation CustomViewBase
+ (void)initialize
{
[SwizleLib swizleMethodsInClass:[self class]];
}
- (BOOL)touchBegin<.....>
{
return YES;
}
#end
And you will create subclasses of CustomViewBase and call super implementation for any methods. (Don't forget that you should create subclasses for UIView, UIControl, UIViewController, UIButton, UITableViewCell).
2.If you do not want to change a base class (you want to use UIView as subclass for your UI classes), you should swizzle methods in your subclasses (since, you do not want to call super).
When subclassing GLKViewController, it has two methods amongst others:
- (void)update,
and - (void)glkView:(GLKView *)view drawInRect:(CGRect)rect.
Both of these methods seem to be called each frame. Documentation reads:
As an alternative to implementing a glkViewControllerUpdate: method in a delegate, your subclass can provide an update method instead. The method must have the following signature:
- (void)update;
Which one should I override in my code, and which of them should contain draw calls?
This thread answers this: Difference between glkView:drawInRect: and glkViewControllerUpdate:? OpenGL ES 2 - iOS
Quoting:
About update() The view controller calls its delegate’s glkViewControllerUpdate: method. Your delegate should update frame data that does not involve rendering the results to the screen.
About drawInRect: the GLKView object makes its OpenGL ES context the current context and binds its framebuffer as the target for OpenGL ES rendering commands. Your delegate method should then draw the view’s contents.
Subclass of UIView
I have a subclass MyView of UIView.
This subclass has a #property UIView * realView.
What I want to do
Whenever a message is sent to MyView, I want to "forward it" to self.realView, excepted for few messages.
For instance, in the implementation of MyView, I would have this override:
- (void)setBackgroundColor:(UIColor *)color
{
[self.realView setBackgroundColor:color] ;
}
Instead of overriding explicitly all the methods, can I do it automatically, at the runtime?
Exceptions
For some methods, I want to have an explicit control. For instance:
- (void)setFrame:(CGRect)frame
{
/* do stuff */
[super setFrame:frame] ;
}
Instead of overriding explicitly all the methods, can I do it automatically, at the runtime?
You implement the -forwardInvocation: method to send any unrecognized messages to the other object. -forwardInvocation is called whenever an object doesn't implement the selector that's passed to it as a sort of second chance to handle a message. You can override it to send the message to another object (which is pretty much what NSProxy does), log the messages, etc.
As #cobbal points out below, -forwardInvocation will help you with methods not implemented in your superview, but it won't handle methods that are implemented int the superview because your MyView inherits implementations of those. For example, if you want to use a UIView as a proxy for a UIButton, all the methods specific to UIButton can be handled by -forwardInvocation:, but those defined by UIView cannot. In order to get a behavior other than the inherited method, you will of course need to override. In some situations you can get around that by deriving MyView from NSObject or UIResponder instead of from UIView, thus avoiding the inherited UIView implementations, but if MyView needs to be a real view you're stuck with overriding each method.
If you think about it, it's hard to imagine how your goal could be met without explicitly overriding each inherited method. You say that you only want to forward most messages, but how can the poor runtime tell which ones you do want to forward and which ones you don't? All it can do is look for a method for the given selector and call it if it finds one, or take some action (like calling -forwardInvocation:) if it doesn't.
Update: #robmayoff points out -forwardingTargetForSelector:, which didn't occur to me but is probably a better solution in your case. It still doesn't handle the situation where you need to redirect methods that you inherit from a superclass, though.
It's entirely possible.
First you need WZProtocolIntercepter. Then use the intercepter as the normal UIView:
WZProtocolInterceptor* fakeView = [[WZProtocolInterceptor alloc]
initWithInterceptedProtocol:#protocol(TheMethodsForTheMiddleManToHandle)];
fakeView.receiver = self.realView;
fakeView.middleMan = self;
[someViewController.view addSubview:fakeView];
Put the methods you want to control in TheMethodsForTheMiddleManToHandle:
#protocol TheMethodsForTheMiddleManToHandle
- (void)setFrame:(CGRect)frame;
#end
I'm trying to category UIViewController to override viewWillAppear:. But getting this warning.
Category is implementing a method which also be implemented in primary
class
#implementation UIViewController (ViewWillAppearCategory)
-(void)viewWillAppear:(BOOL)animated
{
//.........
}
#end
I want to do some stuff during view appear in all screen, So I don't want to touch in all screen. that's why, go with category.
I may implement some method in sub class and I can call that method in all VC(all Screen). But I don't want this. It automatically invoke in view will appear call. Is this any idea to do this or did any mistake in above?
Note: This code will only appear in development phase for some testing purpose. So I'll remove this code when go with app store. So It should be easier task during removal, that is I won't touch all screen. I won't keep this code during submission to app store.
In such cases you must try Method Swizzling, a very nice formed concept which allows you to change the implementation of an existing selector.
For more details and code please visit the link below.
http://nshipster.com/method-swizzling/
categories are for adding new methods, not overriding existing ones. Maybe make a subclass of UIViewController, say, MyUIViewController, with this code:
-(void) viewWillAppear:(BOOL) animated {
// do your "category" stuff
}
then make all your other UIViewControllers subclasses of MyUIViewController with this code:
-(void) viewWillAppear:(BOOL) animated {
[super viewWillAppear:animated];
// rest of code for this class
}
I understand the reasons why you want to have a simple solution to test something on all screens and remove it easily, however:
You can not call super in a category, and not calling [super viewWillAppear:] may have unexpected results depending on the class and its particular implementation.
Swizzling methods is a hack and as you'll remove it from your final version, your testing version becomes useless as it may behave very differently.
On the other hand creating a UIViewController superclass where you properly override viewWillAppear: is not that complicated:
The code will belong only to a single class. No need to repeat/maintain code for every "screen".
You only need to change the other controllers' superclass and Nibs or Storyboards references once.
You can keep the superclass for both testing and release and the behavior will be similar.
You can do so many more things in a superclass than in a category.
Ultimately it would be interesting to know what are you trying to achieve. You could probably achieve similar things by implementing a UINavigationControllerDelegate and keep track of controllers getting pushed and popped.
As for viewWillAppear documentation:
This method is called before the receiver’s view is about to be added
to a view hierarchy and before any animations are configured for
showing the view. You can override this method to perform custom tasks
associated with displaying the view. For example, you might use this
method to change the orientation or style of the status bar to
coordinate with the orientation or style of the view being presented.
If you override this method, you must call super at some point in your implementation.
Again, you can't do that from a category.
As you are saying the code is going to be executed only in debug mode. Then why do you worry about warnings let the warning come you continue your work when it comes to release you remove your Category.
If you don't even need to see the warning your go with your same answer like
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-protocol-method-implementation"
-(void)viewWillAppear:(BOOL)animated
{
NSLog(#"I get callback here too");
}
#pragma clang diagnostic pop
But I would say to go for subclassing because removing the existing class is also not that hard in XCode tool.
What you want to achieve defeats the purpose of a Category. However, there's another way aside from subclassing UIViewController but you have to touch the viewWillAppear method for each controller.
//UIViewController+CustomCategory.h
#interface UIViewConctroller (CustomCategory)
- (void)performCustomization;
#end
//UIViewController+CustomCategory.m
#implementation UIViewController (CustomCategory)
- (void)performCustomization {
// Do custom stuff…
}
#end
Then in each controller
//MYViewController.m
#import "UIViewController+CustomCategory.h"
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
[self performCustomization];
}
This question already has answers here:
Is it possible to make the -init method private in Objective-C?
(9 answers)
how to block a superclass method to be called to a subclass
(5 answers)
Closed 9 years ago.
Suppose you have a UIView subclass. You define an init method "myInitWithFrame: ... andWhatNot:...". You know you won't be using the init method inherited from UIView ever and your custom init method does some vital custom initialising so that you want to force client classes to never use the inherited initWithFrame method.
Is it possible to hide the standard initWithFrame method that was inherited from UIView?
Actually, you can get compile-time warnings about calling a method on a subclass. Use the __attribute((deprecated)) attribute. If you want people to use -initWithPizza: instead of -initWithFrame:, do this:
#interface MyView : UIView
- (id)initWithPizza:(MyPizza *)pizza;
#end
#interface MyView (Deprecations)
- (id)initWithFrame:(CGRect)frame __attribute((deprecated("Use initWithPizza: instead")));
#end
Putting the -initWithFrame: declaration in a separate category is necessary to avoid Xcode complaining that you declared the method in the header but didn't implement it. Since you're just inheriting it from the superclass, that's fine; you don't have to implement it at all. But if you want to implement it to throw an exception, or call through to -initWithPizza: with a default argument, that's fine.
Of course, this won't stop UIKit from calling -initWithFrame: if it was already going to do so. But if you can guarantee that won't happen, then you're fine.
Actually, you CAN restrict with a subclass. You can override whichever methods you want to block in your subclass's .h file. You can make initWithFrame unavailable by placing the following in your .h file.
- (id) initWithFrame:(CGRect) frame __attribute__((unavailable("message")));
This will make the initWithFrame: method unavailable to anyone using your subclass.
To keep other code form calling this method, you can further restrict by putting this in your .m file.
- (id) initWithFrame:(CGRect) frame
{
return nil;
}
No. You can't prevent the users of your subclass from calling the methods of a superclass. You could override them and throw an exception inside, but that would just produce a broken subclass.
Remember that inheritance works as an "is a" extension, that is, instances of your subclasses should behave normally in any context that doesn't know about this particular subclass but knows about its superclass. It's only in places that have explicit knowledge about your subclass that you can benefit from adding extra initialization and other methods.
For example, UIKit has no knowledge of your subclass. So if you want to make your UIView subclass available from a NIB, you need to use the initialization methods that will be called by the NIB loading system, namely initWithCoder:. You can simply call your own initialization methods inside initWithCoder:. But if there are any additional parameters you would like to pass to the init method, you'll have to provide a way to configure them after initialization.