I have a custom uiview class that implements drawRect and is an IBoutlet to my interface builder. I assume this is a pretty standard way of implementing custom views that do their own drawing.
Now, I'm doing my good deed to release all IBOutlets in my view controller's dealloc - however, i noticed that custom view classes do not respond to release - now why would this be? they inherit from UIView, so why does the xcode code sense feature not provide release on them? is it not necessary or possible to release them from memory?
Release the view and set the view variable to nil in the viewDidUnload method of your view controller.
The viewDidUnload method is the recommended place to release IBOutlets.
Related
Most of the time, owners of xib is a UIViewController.
I sort of use it my self.
Still I am confused why.
I suppose, the viewDidLoad and viewWillAppear is kind of the main selling point.
Is that it?
What are the advantage of using UIViewController as owners of an XIB?
A UIViewController object is the main way for views to appear within an iOS window.
Apple provides this as a fundamental, foundational building block (along with so many others) which you can use to build upon quickly and get your app out to market.
And when you subclass UIViewController, you're able to do lots of beautiful customizations which can be collected and eventually turned into (hopefully decent) products. When you subclass a UIViewController, you need to set the "owner" of a XIB file to that subclassed view controller (e.g. ThioViewController), so that way the app knows what object (and user interface) is being instantiated.
Hopefully this isn't too super abstract of an explanation.
First, spend a bit time to understand MVC http://en.wikipedia.org/wiki/Model–view–controller
This is the milestone of Objective-C (not only) development.
UIViewController is controller for all your views (inside this viewController). It provide starting point for you to create views on the screen, manipulate the views, handle actions from views etc.
You can create UIViewController programmatically.
XIB is representation of the screen which you can comfortably operate in Interface Builder to create and customize design of your application screen or one of the screens.
Since XIB represent the screen(view) it must be the controller which controls all the view on the screen - UIViewController or UINavigationController or other type of controller depending of your needs.
Most of time you will subclass UIViewController and use it to achieve you goals.
UIViewController have several subclasses which inherit directly from it (UINavigationController, UITabBarController).
Also UIViewController hav several methods (some of them)
-(void)viewDidLoad
This method is called after the view controller has loaded its view hierarchy into memory. This method is called regardless of whether the view hierarchy was loaded from a nib file or created programmatically in the loadView method. You usually override this method to perform additional initialization on views that were loaded from nib files.
and
-(void)viewWillAppear:(BOOL)animated
Parameters
animated
If YES, the view is being added to the window using an animation.
Discussion
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.
Please check Apple documentation for more information
https://developer.apple.com/LIBRARY/IOS/documentation/UIKit/Reference/UIViewController_Class/Reference/Reference.html
I have a custom view controller with several subviews. Each of those subviews is connected to the view controller's .m file via IBOutlet properties. Those subviews have custom setters that adjust size of the other subviews depending on whether that subview is or is not displaying content.
Now it seems that these custom setters are being called by initWithCoder: prior to viewDidLoad being called. (I hope/assume this is normal.)
My issue is that calling self.view accesses the setter methods for self.view's subviews. My current understanding is that this should not be necessary. Can someone explain what's going on here? I'd rather this not happen as I'm not intending to set anything by accessing self.view.
Here is the code: https://github.com/kenmhaggerty/Sandbox
Calling self.view on a view controller causes it to load its view from the nib, if it hasn't already done so. This instantiates all objects in the nib (using initWithCoder:) and sets the values of any outlets (using your accessor methods). It then calls viewDidLoad, by which point everything in the nib will exist.
Your outlet setter methods are probably not an appropriate place to be making layout adjustments. Either use a constraint-based layout which will automatically adapt to changes in size of the subviews, or use viewDidLayoutSubviews, or use the methods you are using to pass model information to those subviews.
I believe that UIView objects can delegate control to views in iOS programming. However, I thought this was already handled by an IBAction associated with an IBOutlet corresponding to the UIView.
In that case, what does it mean to drag a blue line (while pressing Ctrl) from the delegate circle of the UIView in my xib to File Owner?
Isn't the UIView already delegating to my view controller via an IBAction? The code seems to work if I don't specify anything for my UIView's delegate.
"Isn't the UIView already delegating to my view controller via an IBAction? The code seems to work if I don't specify anything for my UIView's delegate".
It looks like you're confusing the idea of the Target-Action Mechanism with delegation. While you could in a way think of target-action as involving “delegation”, it would only be in the most general sense of the word in that it’s the target (generally a controller) that handles and implements the action (the message). However, a Cocoa programmer would probably refrain from explaining the target-action mechanism by using that particular word – delegation – as it would be too easy to confuse it with actual Delegation.
When you “wire up” buttons and controls in the nib file to call IBAction methods in your controller object, that’s just the target-action mechanism at work. As you saw, the code works even if you "don't specify anything for my UIView delegate”, since target-action doesn’t involve delegation (in the Cocoa-sense of the word).
Delegation is generally used as an easier alternative to using subclassing to implement the desired behavior. For example, instead of having to create your own custom subclass of UITableView in order to have it know what data you want it to display, you can simply use the plain UITableView class, set its delegate to a controller class, and have the controller class implement the required/desired designated delegate methods. Using subclassing to accomplish that could potentially get complicated, since when you subclass, you need to have a full understanding of the inheritance chain and how all of the superclasses work.
File's Owner is just a fancy way of disguising the name of the class that the XIB is taking it's references from. When you drag the delegate outlet to your class, it's the equivalent of this line:
[self.myControl setDelegate:self];
When you drag while pressing CNTRL from an IBOutlet or IBAction to a UILabel, UIButton or something else, you are binding events or outlets to your controller.
A delegate sort of a controller that must implement specific functions depending on which type of delegate it is. For example, the UIViewController, which implements the UIViewDelegate protocol, can implement
-(void)viewDidLoad
the YourApplicationDelegate, which implements UIApplicationDelegate must implement
-(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
So a delegate is just a set of functions which define the behavior of an object, the classes that implement them can change this behavior.
I want to run some code when any UIView is loaded from the resources.
How can I do that, without having to modify implementation of each UIView subclass?
Note: subclassing UIView is not an option.
You should subclass UIView and then use your subclass for all your others UIviews
You could consider creating a UIView, which will be the base view class to all your UIView as suggested by #gsempe and implement the willMoveToSuperview: method.
From Documentation.
Tells the view that its superview is
about to change to the specified
superview.
- (void)willMoveToSuperview:(UIView *)newSuperview;
- (void)willMoveToWindow:(UIWindow *)newWindow;
Since we are talking resources and NIB implicitly, I can recollect only two methods in which you would load a view – UIViewController's initWithNibName:bundle or loadNibNamed:owner:options: although there might be some private methods that we aren't provided access to.
So you can think of overriding behavior there. You can create a custom UIViewController subclass that will be the parent for all your view controller's and subclass NSBundle to override loadNibNamed:owner:options:. But this might depend on what kind of task you want to accomplish.
You can try declaring your own category and override a method, but I don't think that would be a good practice. Other way is to extend the UIView subclass and override the method you want. And use that class in your application instead of UIView.
So the approach really depends on your use case.
I'm trying to understand how these two are connected. Every time you make a UIViewController does it also automatically come with its own UIView?
Also are these from Cocoa or Objective-C?
UIViewController is a Cocoa Touch class built for the purpose of managing UIViews. It expects to have a view hierarchy, but you don't "automatically" get a view (this is slightly inaccurate; see edit below). Usually you will obtain views by calling initWithNibName on your view controller.
There is some built-in magic in Interface Builder which knows that if File's Owner is a UIViewController (or subclass), there is a property called view. That's about it.
Once you have linked a view controller and a view, the view controller does a fair amount of work for you: it registers as a responder for view touch events, registers for device rotation notifications (and handles them automatically, if you wish), helps you take care of some of the details of animation, and handles low-memory conditions semi-automatically.
Edit: correction—if you don't call initWithNibName or set the view property manually, the view property getter will invoke loadView if view is nil. The default implementation of loadView will see if you've set nibBundle and nibName and attempt to load the view from there (which is why you don't have to call initWithNibName, most of the time), but if those properties aren't set, it will instantiate a UIView object with default values. So technically, yes, it does automatically come with its own UIView, but most of the time that's of little value.
UIViewController doesn't automatically come with a view. You have to make a view in the -loadView method. By default, this loads the view from the nib file you've specified. You can also override this method to make a custom view if you prefer not to use a nib.
Also, the view is not created right when the UIViewController is created. UIViewController uses a technique known as lazy-loading to defer the creation of a view until the view is actually accessed for the first time.