I am loading a UIView from a NIB file with outlets and I want to change the properties of these outlets. I am wondering when I should do that because in the init method the outlets are nil and that make sense and in the drawRect method I can change the properties of my outlets but I'm not sure it's the proper way to do that.
Is there a method called after the init method and the drawRect method where I could do what I want ?
Thank you.
There's layoutSubviews - this will definitely be called before the first call to drawRect?
The UIViewController method viewDidLoad is called after a nib has been loaded and after loadView is called. (loadView allows you to load a view programmatically instead of using a nib. However, nibs are much better so it's best to pretend that loadView doesn't exist.)
NSObject implements awakeFromNib. awakeFromNib is called after an object has been loaded from a nib. Here's a quote from the docs:
Typically, you implement awakeFromNib for objects that require additional set up that cannot be done at design time. For example, you might use this method to customize the default configuration of any controls to match user preferences or the values in other controls. You might also use it to restore individual controls to some previous state of your application.
drawRect: is a UIView method, only use it if you need to do Quartz drawing. Using layers and Core Animation is more efficient. If you want to configure a custom UIView (i.e. you've subclassed UIView instead of configuring a view within a UIViewController) then you should use initWithCoder:.
If you want to use IBOutlets in your initialization code for a UIView - override awakeFromNib. This is the first method called after outlets have been configured.
With regard to UIViewController - viewDidLoad and viewDidAppear are often convenient locations to put your initialization code in but beware: autolayout has not happened at this stage which means strange autoresizing effects can cause you bother. The better solution is to put your code in viewDidLayoutSubviews which is the first lifecycle method called after autolayout.
Related
I have a subclass of UIViewController that I want to add from the storyboard.
So I'm using what seems the standard methodology:
SubViewController *svc = [self.storyboard instantiateViewControllerWithIdentifier:#"SubViewControllerID"];
[self addChildViewController:svc];
[self.view addSubview:svc.view];
Which is fine but what if I want to call a custom init method on the subview?
I can do something like:
svc = [svc initWithFoo:#"Hello"];
Which seems to have to go after the addSubview call inorder for it to work.
Is this the best way to do this?
Seems a bit unorthodox. Calling an init method on an object that has already been created seems like its no longer truly an init method.
Maybe I should call it setWithFoo: or something and not have it return anything?
SubViewController *svc = [self.storyboard instantiateViewControllerWithIdentifier:#"SubViewControllerID"];
will cause the SubViewController to be inited with it's - (id)initWithCoder:(NSCoder *)decoder {} method.
Override that method (don't forget to call super)
If you want to do additional setup to your view controller after you instantiate it form the storyboard you can create some methods in the view controller's class and call them after the instantiate method fo the storyboard.
But be careful, if you try to make changes on any UI component in those methods, they wont be applied, and probably the app will crash. So use those methods to set params to the View Controller like array of objects, or any kind of data, and apply the UI changes for the view controller's view in viewDidLoad/viewWillAppear/viewDidAppear methods of your view controller.
Essentially I think the answer is that you can't use custom initialisers on ViewControllers added from the storyboard. Instead you have to set properties directly or through a method at the appropriate time in the life cycle as stated above.
Also as mentioned, the VC will be instantiated through initWithCoder, so calling an additional initialiser might be superfluous(?).
I encountered problems trying to use a custom initialiser that contains a call to super if I called it before the subview was added. I would just get a blank view added, I think because the superclass doesn't seem to know about the storyboard at that point. I had more success removing the call to super but that seems wrong.
This case would be more pertinent when adding subviews to a scrollview. For simplicity I left this out of my example.
I have a UIView subclass which currently assembles itself completely programatically. It has a custom initWithFrame:bundle: initializer which is necessary because it uses the bundle passed in to load image resources.
I want to make this view a subview in a larger nib file, but then initWithCoder will be called when the nib loading code gets to it instead of my custom initializer. Is there any way I can place this view in a nib and still have my custom initialization occur?
Yes, you can override initWithCoder: too if your bundle is known ahead of time (read: You don't need it passed in as a parameter). Otherwise, nope.
If you can wait until awakeFromNib, you can do your initialization in there. You still have the problem of not being able to pass the bundle into the method, though. Since awakeFromNib is called after initialization and setup of all outlets and actions, it might be too late for you. Maybe it's better to redesign around the nib-loading system anyway?
Ran into something interesting, want to know if I'm doing something wrong or if this is the correct behavior.
I have a custom UITableViewController. I ASSUMED (first mistake) that if you initialize as such:
[[CustomTableController alloc] init];
it would automatically load from a XIB of the same name, CustomTableController.xib, if it is in the same directory and such.
HOWEVER
This does not work; doesn't load the XIB. BUT, if I change the parent class of my controller from 'UITableViewController' to 'UIViewController', EVERYHTING WORKS FINE!
Calling:
[[CustomTableController alloc] init];
loads the controller and view from my xib.
Am I doing something wrong? Is this a bug? Expected behavior?
Most of the classes in Cocoa Touch list a "designated initializer" that you're supposed to call from your init methods when you subclass them. When you create your own custom class, it's a good idea to check the documentation to find the designated initializer for your superclass. When you initialize the class using some other initializer from a more general superclass (which you're doing by calling - [NSObject init] in this case), you rob your direct superclass of its opportunity to properly initialize its state. Sometimes you can get away with this. Often you can't.
UIViewController's documentation states that its designated initializer is -initWithNibName:bundle:. If you call this method with a nil nibName, it will look for a nib that matches your class name. The behavior of -init is undocumented for UIViewController. Based on the behavior you're seeing, it seems like it may be calling [self initWithNibName:nil bundle:nil], but it would be safer to call initWithNibName:bundle: directly rather than relying on this undocumented behavior.
UITableViewController only defines a single initializer, -initWithStyle: (although it doesn't specify this method as the designated initializer). This method initializes your UITableViewController without using a nib, which is usually fine. Since you don't add subviews to a UITableView, there usually isn't much to be gained by configuring your UITableViewController via a nib.
If decide you want to configure your UITableViewController via a nib anyway, the documentation tells us that we can safely bypass -initWithStyle: and call UIViewController's initWithNibName:bundle: method. Here is what the documentation tells us about how our UITableView and its controller will be initialized in each case:
If a nib file is specified via the initWithNibName:bundle: method (which is declared by the superclass UIViewController), UITableViewController loads the table view archived in the nib file. Otherwise, it creates an unconfigured UITableView object with the correct dimensions and autoresize mask. You can access this view through the tableView property.
If a nib file containing the table view is loaded, the data source and delegate become those objects defined in the nib file (if any). If no nib file is specified or if the nib file defines no data source or delegate, UITableViewController sets the data source and the delegate of the table view to self.
In summary, the documentation for most Cocoa Touch classes either specify a single designated initializer or a handful of initializers that you can call safely from your subclasses. Always refer to the documentation for your superclass to figure out which initializer your subclass should call.
I messing with iphone developement. I have a uiimageview subclass that I want to use to detect touches. I have sucessfully added to interfacebuilder and I can detect a touch in my UIImageview subclass within my application so all is good on that front. however my UIImageView subclass has a custom initializer which is not called when it is created in interface builder.
if I manually initialize the UIImageview and add it programmatically I think it will work but then I lose the ability to 'see' my positioning in Interface builder.
how can I either
1) 'see' a uiimageview in interface builder that is added in code? (not possible?)
2) call my custom initializer when the subclass is instantiated in interfacebuilder.
thanks
Hi thanks for suggestions. I think I'm getting closer to understanding the relationship between the xib and the viewcontroller.
I now am sucessfully adding my UIImageView subclass programmatically and using my custom initiializer which overrides InitWithFrame.
I think I read that the xib calls 'awakeFromNib' so I could equally add my iniitialization code in there. I like the idea of adding it programmatically as I have more control (although harderto set up my IU)
so one more realted question. if I add an UIImageView subclass in interface builder. I can see it and detect touches on it. if I want to refer to it in the view controller class do I have a pointer to it? i.e. is there a variable name for it? the UIImageViews I create myself I obviuosly know what they are called.....
You likely have put your instructions in the wrong initializer.
According to the documentation, objects unarchived from a NIB are initialized with initWithCode: if they conform to the NSCoding protocol; objects that don't conform to NSCoding are initialized with init.
In this particular case, UIImageView does conform to NSCoding. It's likely that you have you intended for initWithFrame: to be called and put your instructions in that method.
Can you not simply put your initialisation logic in viewDidLoad? In particular,
-(void)viewDidLoad {
[super viewDidLoad];
// Put whatever was in your custom initialiser here.
}
i set my view controller to the particular view through Interfacebuilder.
but initWithFrame is not calling , but drawRect is being called?when i put break point?
Right, because it's not guaranteed that initWithFrame: will be called when unarchiving the xib. Try using awakeFromNib or viewWillLoad or viewDidLoad. Which one you choose will mainly depend on at what stage during the display process you need to insert your code.
Also, check out the answer to this question.
According to the documentation - http://developer.apple.com/library/ios/#documentation/uikit/reference/UIView_Class/UIView/UIView.html - initWithFrame: is not called when your view objects are subsequently loaded from the nib file. Objects in a nib file are reconstituted and then initialized using their initWithCoder: method, which modifies the attributes of the view to match the attributes stored in the nib file.