Just as a matter of curiosity, how does the nextResponder method implementation of the UIView class know who is the UIViewController that manages the view?
The UIResponder documentation states this, and I can see it work, but I don't quite understand it. To the best of my knowledge, a UIView does not maintain a reference to it's controller, so what's happening behind the scenes? Or am I just missing something obvious?
I'm still very new to Objective-C and iPhone development so I apologize if this is something obvious, but I am quite curious.
Thanks!
The responder chain is separate from the view hierarchy. The responder chain might look like this:
First Responder > View Hierarchy > Window > Window Delegate > etc...
However, objects can insert themselves into the responder chain and that's what UIViewController does. From the docs:
Because view controllers are tightly bound to the views they manage, they are also part of the responder chain used to handle events. View controllers are themselves descendants of the UIResponder class and are inserted into the responder chain between the managed view and its superview.
In Big Cocoa, this is accomplished using the -setNextResponder: method. That method isn't public in Cocoa Touch, but nevertheless that's what UIViewController appears to do.
If you look at UIView.h, you can see a member variable named _viewDelegate that is of type UIViewController*, this is probably where the view controller reference is stored when the viewcontroller's view property is set, and where it knows to look when you call nextResponder.
there is actually a private api on uiview to get the uiviewcontroller it belongs to. Very handy ;)
My guess is when a view is added to a view controller(controller.view) this property is set.
My guess is that the system may maintain a mapping between UIViewController objects and their root UIView objects. The code for traversal of responder chain may use this mapping to pass the event to the corresponding UIViewController object.
Typically subviews are added using:
subview = [viewController view]
[superview addSubview subview]
addSubview method automatically sets superview as the next responder for subview, so:
a) viewController wont have the opportunity to insert itself between superview and subview.
b) viewController does not know about superview, hence it cannot set it as its next responder.
c) Apple recommends that a view may not be shared across controllers. In absence of multi-threading this restriction makes sense only if there is a map of views and view controllers.
Related
I need to create a class that will present a UIVIew and has a some code to initialize it before it is ready to show. I need to know when the view is ready, I mean, I need something like viewDidLoad or viewWillAppear, but as it is a UIVIew it lacks these protocols.
I cannot implement it as a UIViewController as I don't want to present it modal. It is really a rectangular view that needs to show on a screen side.
How do I declare this class? If the class is a UIView based I don't have the methods I mentioned.
thanks
Any reason to not do that kind of stuff inside the initWithFrame method on a UIView? Also, you can do additional stuff on layoutSubviews. A view controller has viewDidLoad because the view is lazy loaded (from a nib or otherwise - it also has a loadView). It has viewWillAppear and viewWillDisappear because it is managing the view (btw, even the view controller is managed by another view controller - these methods are called when you have the controller within a UINavigationController or UITabBarController or such classes which mange UIViewControllers. - the view itself is not really managing anything. All it knows about is how to draw itself. For that, you have layoutSubViews, drawRect, etc.
Doing some heavy stuff upon view's load will definitely kill the UI performance. You probably need to implement another kind of design pattern that will asynchrounously assign data values to the instance of your custom view - when that is done, you call layoutSubviews or setNeedsDisplay to update the view.
The scenario you described is no reason for not implementing a UIViewController. Assume you have a container view A and a subview B. Both have their own UIViewController AC and BC. Now on AC you add the View B managed by BC:
[self.view addSubview:BC.view];
You probably want to be using UIViewController.
You don't just have to present them modally. You can get your view controller's view with yourViewController.view, and add that as a subview of whatever view you want.
If you're targeting iOS 5, there are a few new methods (such as addChildViewController:) designed to make doing things like this easier. You can do it on iOS 4 too though, and it'll still work.
Implement a drawRect in youR UIView, plus an initialization flag. Just before the view is to be displayed the drawRect will be called. If the initialization flag isn't yet set, do your initialization and set the flag. This will only look good if your initialization can be done quickly (no long synchronous calls).
I need to create a class that will present a UIVIew and has a some code to initialize it before it is ready to show. I need to know when the view is ready, I mean, I need something like viewDidLoad or viewWillAppear, but as it is a UIVIew it lacks these protocols.
You might want to rethink how your view is being used. It sounds like you're trying to put too much controller-like logic into your view. That's why you're wanting your view to behave like a controller.
More specifically: What exactly are you trying to accomplish? If you're waiting for data to load before display the view, that might actually be something to put in the controller that is calling the view.
To illustrate my point, imagine you're putting some text in a UILabel that you read from disk. The reading from disk isn't really related to the view. The view only cares what text it displays, not how it received the text. Once it's read from disk, you can create a UILabel with that text that you read. This allows the UILabel to be more flexible.
That example might not be at all related to what you're doing, but I use it as an example of the difference between a view and a controller. Anything not related with the display and drawing of the view shouldn't belong there.
From within a UIViewController, I programmatically create about 10 instances of a CustomUIView and place them on the [UIViewController view].
When any of those instances of CustomUIView is touched, I want to let the controller know and take some action.
I've thought of two ways to do this:
Subscribe the UIViewController as an observer to the CustomUIView. Then when touchesBegan:withEvent: is fired, call a method on the UIViewController observer.
Use [self.nextResponder touchesBegan:touches withEvent:event] to raise the event to the UIViewController.
I've implemented both, and they both work ok.
Question: What is the best way for a programmatically-created view to communicate with its UIViewController? Is one of these the way to go? Or is there a third way?
The resources I've found online are very good at explaining all the Cocoa "pieces", but I'm having trouble finding best practices for overall architecture.
For the case of touch events, you don't have to do anything!
From the UIViewController class reference:
View controllers are tightly bound to the views they manage and take part in the responder chain used to handle events. View controllers are themselves descendants of the UIResponder class and are inserted into the responder chain between the managed root view and its superview, which typically belongs to a different view controller. If the view controller’s view does not handle an event, the view controller itself has the option of handling the event before passing the event along to the superview.
This means your view controller can handle touch events in its view without any extra setup, as long as you don't handle them in your view.
You would make the UIViewController the delegate for the UIViews, if you want the views to be able to communicate back to the controller.
Touch events will automatically get sent to the Controller as part of the responder chain.
I have created an UIView in my iPhone app. I want to handle something when user closes or opens when UIView is present as current screen. I thought, i can do this under viewWillAppear:. But, viewWillAppear: is not called in UIView. Does it work only on UIViewController? How can i handle viewWillAppear: or viewDidAppear: for an UIView?
Update: UIView what I created everything through program, not in .xib.
Please advise.
Thanks!
From your message I infer that you wrote your viewWillAppear: method on the UIView class. As you suspect, that method is part of [UIViewController]1, not [UIView]2 therefore it only gets called on the UIViewController.
You should connect the property view of the UIViewController to the UIView object in the interface builder and then implement that method in the UIViewController.
If your view is created in response to an user action,
Update for your update:
You should tag the views either in code (view.tag=1) or IB.
Then you can do if (self.window.rootViewController.view.tag == 1) { ... } from your delegate (assuming you are looking for the view of the controller who is the rootController, otherwise post more details).
It's even better if you define constants on one place instead writing 1 as a literal.
These delegate methods are called every time the superview is presented to the screen and should be implemented in the UIViewControllers.
The gotcha is that these methods aren't called when subviews are presented on the screen, so your superview-view-controller will have to respond to these events accordingly.
You can find more information in this post here.
If you study the documentation for UIView and UIViewController what you will find is -(void)viewWillAppear:animated: is a method of UIViewController and not of UIView, so in order to use it, it must be implemented by subclassing UIViewController. Generally for best practice if you want to follow MVC, any functionality that does not pertain to the view itself should be delegated to the view controller and not be in the body of your UIView subclass.
Create a new view controller with xib file, and then link your custom view class to the view in your xib file.
MyViewController.xib has File's Owner class set to MyViewController (a subclass of UIViewController) and File's Owner view connected to a UIView containing some subviews.
OtherViewController.xib has File's Owner class set to UIViewController and File's Owner view connected to an empty UIView.
Is it possible in Interface Builder to embed MyViewController's view inside the view in OtherViewController.xib?
I tried adding an instance of MyViewController into OtherViewController.xib, but I can't drop it inside the view (because it's not a UIView) and I can't get to the view that was associated with MyViewController in MyViewController.xib (only the view controller itself, and nothing it's connected to, makes it over to OtherViewController.xib).
You probably do not want to do this. Follow the warning in the View Controller Programming Guide:
Note: If you want to divide a view hierarchy into multiple subareas and manage each one separately, use generic controller objects (custom objects descending from NSObject) instead of view controller objects to manage each subarea. Then use a single view controller object to manage the generic controller objects.
A UIViewController subclass whose view does not fill the window will not behave as you might expect. It will not receive view controller lifecycle messages, rotation messages, or have its parentView/navigation/tabBarController properties set correctly.
A UITableViewCell should not be the view for a UIViewController. It might have some controller object responsible for managing its behavior (though I suspect this behavior can probably all be contained within the cell view itself) but that controller should not inherit from UIViewController.
This has changed since some of the other answers were posted - you want to take a look at the latest documentation for UIViewController, particularly the guide section "Presenting View Controllers from Other View Controllers" and the class reference guide section "Implementing a Container View Controller". Also, there's a video from WWDC 2012 covering the topic on iTunes: Session 236 - The Evolution of View Controllers on iOS. (The video is very useful, it's not just a general overview.)
You can put it all in one xib. For example, just put it all in your MainWindow.xib.
This can be done programmaticly by adding a reference in OtherViewController to MyViewController. This is perhaps a bit messy and does in some way lead me to ask why you would want to do this but... I will trust that you know what you're doing.
Warning. Because 'Other' will contain a reference to 'My' you will want retain My inside Other. but Do not, I repeat do not retain 'Other' inside of 'My' this kind of cycle will lead to errors.
Good luck and don't forget to vote
ps if you have a little more detail I may be able to help you sort out a better design so that this sort of thing can be avoided :)
I have a relatively simple app. I have a fullscreen UIView subclass (musicGridView) that the user interacts with, and a UIScrollView subclass (scrollView) that loads this class in, as well as a ViewController and mainWindow.xib.
Right now, I have a viewController instance loaded in the nib, which is of type myViewController. The nib also has instance of myUIView, which the myViewController is pointed to.
In AppDelegate, I do this:
[window addSubview:scrollView];
[scrollView addSubview: viewController.view];
scrollView.musicGridView = (MusicGridView*) viewController.view;
which I think is wrong. Ideally, the appDelegate doesn't have an instance of scrollView.
In scrollView's AwakeFromNib class, I do the initialization on the scrollView.
The way I think it should go, is load the [window addSubview:viewController.view] in appDelegate, and then point the viewController to an instance of scrollView instead of musicGridView. Then, in scrollView awakeFromNib add a subview of musicGridView.
Eventually, I want to create another view owned by scrollView that is actually a side TabBar (which isn't possible with the given API's) that the user can scroll to the left to reach.
So I guess amongst other MVC stuff, the question is, should the viewController point to the scrollView, which contains all other content UIView subclasses, including musicGridView?
It sounds like you are not using Interface Builder to design your UI. Since this is a new project, I would suggest doing that. You should not have to write any code like this at all. You will however need to describe your outlets and actions.
The two most important things you need to know when dealing with IB are the IBOutlet and IBAction keywords.
Sample class header:
#interface MyClass : NSObject {
IBOutlet UIScrollView* myScrollView;
}
- (IBAction) doWork;
#end
Now you can wire these two things up using Interface Builder by dragging sources to destinations with your mouse. YouTube has lots of tutorial videos on IB if you need a better description of how to do this.
I'm someone who doesn't use Interface Builder for UI design; in my experience, you need to go either all-IB, or all-programmatic. To solve your particular problem, I think you need your musicGridView to be an instance or extension of UIScrollView.
This can be done in your custom viewController's loadView method - simply initialize it to a UIScrollView (and add things to it), instead of a plain old UIView.
However, as described above, this approach isn't compatible with an IB-centric approach, as is confirmed in the UIViewController Class Reference
All subclasses of UIViewController
should implement the loadView method
to set the view property unless you
load your view from a nib file.