I'm trying to add custom properties to the UIView so I can use them among all UIView objects and all the UIView's subclasses, like UIImageView, UISlider ... etc
I've tried to use Category to do so, but it turns out I can't use instance variables in the Categories' properties. So, I canceled this solution.
I, also, have tried to use Inheritance to do so, as if I made UIView subclass and added all the properties that I want to. But in this case I do get my additional properties for all of my custom class instances, but I don't get them for any of the other UIView subclasses, like UIImageView.
I'm trying to figure it out but I couldn't.
At the end, I figured a solution to my problem. I'm not sure if it was the best one but it does work for me.
I've used a runtime feature of the Objective-C 2.0 which called: Associated Objects.
This feature gives me the ability to add custom properties to any class using Categories.
I found those resources helpful:
• http://nshipster.com/associated-objects/
• http://www.youtube.com/watch?v=VxUjilPe5Do
Related
I have a class that defines all styles on a UIVIew.
They are all predefined but I'm not sure when to fire this.
When I try to create an extension for this:
extension UIView
{
func willMoveToSuperview(newSuperview: UIView?)
{
self.stylize() // Another extension somewhere (not here my problem)
}
}
And I'm getting this error:
Method 'willMoveToSuperview' with Objective-C selector conflicts with
previews declaration with the same Objective-c selector
I have tried to override it, but didn't worked either.
Any ideas on how to be able to apply a same behaviour when all of my UIViews will become visible?
You can use Swizzling technic to customize UIView's function. Take a look at:
http://nshipster.com/method-swizzling/ (objective-c)
or
http://nshipster.com/swift-objc-runtime/ (swift)
Hope that helps.
Even though Swift's Extensions are similar to Categories from Objective-C, what you are trying to do is not allowed in Swift.
You cannot override existing functionality:
Extensions can add new functionality to a type, but they cannot override existing functionality.
Source: Swift Extensions - Apple Documentation
Depending on what it is that you are trying to style, you might want to take a look at UIAppearance, it will allow you to style default colors for the UINavigationBar, amongst other things. NSHipster has a good post about it: NSHipster - UIAppearance
You can create a subclass of UIView with the method .stylize().
Then each view you create, you inherit of you UIView subclass.
You'll be able to cal .stylize() on each UIViewSubclass. Simply write the style code inside the subclass and inherite.
Or
Use a category to add the method to the existing UIView class.
See : https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/CustomizingExistingClasses/CustomizingExistingClasses.html
Outside of swizzling (not generally recommended), or subclassing as noted by David in his answer, there isn't really a way to override existing methods on a class and its subclasses.
One thing you might try is creating a base class for your view controller instead of all your views. In your view controller base class, you could override viewWillLayoutSubviews to recurse through the view hierarchy and call stylize on each view. This means you would be using the subclass approach in fewer places (just view controllers as opposed to all views).
Another thing you might consider if taking the subclassing approach with UIView is that if you are subclassing anyway, you can take advantage of things like #IBDesignable and #IBInspectable to better integrate those UIView subclasses with storyboards and live preview.
I wrote a Swift library which does exactly this, and it works well for the type of styling it seems you want to do: https://github.com/daniel-hall/Stylish
Recently I've been looking into RESideMenu. What really piqued my interest was his 'UIViewController+RESideMenu.h/m'. It appears to me that this is a way to subclass a UIViewController. It includes IBActions and methods in it that are accessible from anything that inherits from UIViewController.
All of my attempts to replicate this have failed. Is there a special way to go about it?
Usually that sort of classname is used to denote a category. Instead of subclassing it adds additional methods and properties to a class. For more information see here: CustomizingExistingClasses
A quick question from a wanna-be iOS developer. I want to create a UI for an iPhone app without Interface Builder, only programmatically. However, I want to stick to MVC recommendations and separate V and C and have a clean readable code, therefore:
I create UIView class files (e.x. SplashView.h and SplashView.m)
I create UIViewController class files (SplashViewController.h and SplashViewController.m)
I define my UI elements (view, subviews, buttons and text fields) in the UIView class files
I load the main view in view controller's loadView method, and then do other things in view controller's viewDidLoad method
Is this a correct approach to begin with?
Second part of the question, independent of Y/N answer to the first. Where do I define these custom UI elements?
- Inside the view's initWithFrame: method?
- In separate (property getter? property setter?) methods? I.e. do I have to declare each UI element as a property first in the .h file?
If these questions sound a bit ignorant, it must be because they are :) I found lots of sample code on StackOverflow, but little to indicate where you actually put it. I would be really grateful for any help, especially if you could paste/reference some relevant code.
Your list is correct. This is how I do all of my apps. No Interface Builder, just code.
Each custom view typically creates its own subviews in an appropriate initXXX method. This could be initWithFrame: but you could define others as needed. Subview layout can be done through constraints, autoresizing masks, or by implementing layoutSubview.
Each view controller would instantiate its needed views in the viewDidLoad. View layout can be done with constraints, autoresizing masks, or by implementing viewWillLayoutSubviews.
The use of properties is completely optional. Create public properties for anything to be set/get from an outside class. Optionally create private properties for values internal to the implementation.
Go to the Apple website for Sample Code; download everything that you can for applications that are similar to your goal.
I'm working on an accessibility project for an iOS application. Because accessibility does not act quite as advertised, I have to override accessibilityFrame, accessibilityActivationPoint and pointInside:withEvent in a subclass in order to expand the region recognized by VoiceOver (for both drawing and touch recognition) beyond the "natural" bounds of the control view. So, in order to change the VoiceOver bounds of a UIButton I have to subclass that class and then add these three methods. In order to do this for a UILabel I have to add another subclass with the code, and so on.
I can refactor the code in these methods to a central location, but I was wondering if this can be done more elegantly with inheritance. I'd like to put this code into a subclass of UIView (maybe called UIViewAccessible) and then create a subclass of UIButton called UIButtonAccessible which inherits from UIButton which would in turn inherit from UIViewAccessible instead of UIView. Is this possible, or can something like this be done with a category?
Edit: According to the docs, you can't really achieve this with a category:
If the name of a method declared in a category is the same as a method in the original class, or a method in another category on the same class (or even a superclass), the behavior is undefined as to which method implementation is used at runtime.
Is there some other way to do this?
To answer your question, no, it can't, since your UIViewAccessible is a second degree sibling to UIButton in the inheritance chain (both inherit from UIView at some point). But I guess you already knew that. As for a solution, you could wrap around your UIView accessible classes a decorator and use protocols for strong typing. That way you'll keep the code in one place. I've described this technique here in more detail (although for a different purpose, it's the same situation).
For the views that would support accessibility you'll have to do this:
#property (nonatomic, strong) UIView<MyAccesibilityProtocol>* view;
//self.view can come from the nib or previously created in code
self.view = [[AccesibilityDecorator alloc] initWithDecoratedObject:self.view];
//you can then use self.view like any other UIView,
//and because it also implements an
//accessibility protocol, you can use the methods
//implemented in the wrapper as well.
//more than that, you can control which methods to override
//in the AccesibilityDecorator class
[self.view addSubview:otherView];//could be overridden or not
[self.view myAccesibilityMethod];//custom method declared in the protocol
In my application I want to associate NSMutableDictionary to all UIElements (UIButton, UILable, etc), I can easily achieve this by subclassing each element, but I just want to know if I can make my own UIControl subclass -with a property of type NSMutableDictionary-, as superclass of all programmatically created UIElement s in anyway, so that I can reduce the number of subclasses.
Here like this
#interface UIControl : MyControls
{
}
#property(nonatomic,retain) NSMutableDictionary *details;
#end
and make MyControls as superclass of all programmatically created UIElements
You can do this, not by subclassing, but by adding your own properties and methods to UIControl itself (the superclass of UIButton, UILabel, etc.). These will then be inherited by any standard buttons, labels, etc. that you instantiate. Objective-C lets you add your own methods very easily using Categories. However, you can't add instance variables via categories. To do that, you need to use Associative References which are documented in the Objective-C Runtime Reference.
There's a good tutorial on how to do this here.
By the way, I don't necessarily disagree with inturbidus. But if you're sure you want to go this route, that's how you'd do it.