Is there any function that is similar to viewWillAppear() for UIIbutton classes?
All these functions below are called only once
prepareForInterfaceBuilder()
awakeFromNib()
init()
So not exactly like a viewWillAppear, No.
This is because these are fundamentally different aspects of the architecture. One is usually the manager(a viewController), and the other always is a minion(UIView).
Their lifecycles are naturally different.
But if you want to perform a change in your custom view, whether a UIButton or any other UIView subclass, what you can do to reset is to use the method setNeedsLayout().
From the apple docs
Call this method on your application’s main thread when you want to
adjust the layout of a view’s subviews. This method makes a note of
the request and returns immediately. Because this method does not
force an immediate update, but instead waits for the next update
cycle, you can use it to invalidate the layout of multiple views
before any of those views are updated. This behavior allows you to
consolidate all of your layout updates to one update cycle, which is
usually better for performance.
Blockquote
You should perform further operations on the setting of the view by overriding
the layoutSubviews() method
Again, from the docs
Subclasses can override this method as needed to perform more precise
layout of their subviews. You should override this method only if the
autoresizing and constraint-based behaviors of the subviews do not
offer the behavior you want. You can use your implementation to set
the frame rectangles of your subviews directly. You should not call
this method directly. If you want to force a layout update, call the
setNeedsLayout() method instead to do so prior to the next drawing
update. If you want to update the layout of your views immediately,
call the layoutIfNeeded() method.
Hope I have been clear in the explanation.
You can also post your exact situation with code for more clarity and answers.
There is no strait way to do it: UILabel, UIButton haven't such functions because they are inherited from UIControl -> UIView -> UIResponder these classes haven't such functionality.
What you can to do: in your main controller which contains buttons and labels you can call custom method at viewWillAppear which will update content on your custom elements.
PS. Elements you can organize like an array or also check super views and based on protocol / class call your custom method.
With the help of Abhishek Arora, I was able to change the UILabel's textColor this way.
override func setNeedsLayout() {
tintColor = .clear
}
override func tintColorDidChange() {
print("TINT COLOR DID CHANGE")
textColor = .blue
}
}
Related
In iOS, if UILabel inherits from UIView then why isn't the animate method available to UILabel and how would I have known to go up the class? I know its probably private to the UIView class but wouldn't it make sense to have it directly available to UILabel as well? How does Apple or developers dictate what methods should or should not be available?
Here's an example:
func animateLabelTransitions(){
UIView.animate(withDuration: 3.5, animations: {self.questionLabel.alpha = 1})
}
The animate methods are available to UILabel. They are class methods of UIView which means they are class methods of any subclass of UIView as well.
While pointless, you could have written your code as:
func animateLabelTransitions(){
UILabel.animate(withDuration: 3.5, animations {
self.questionLabel.alpha = 1
})
}
But what's the point? This would confuse a lot of people. Just call the animate methods on UIView.
Just because you call animate on UIView doesn't mean it restricts what you can put inside the animation or completion blocks.
animate is a class method, not an instance method; it applies to all views simultaneously, not some specific view. There's no need to specify which one thing you're trying to animate. You can put many things in the block and animate them all together. What would you expect to happen if you called UILabel.animate(...) and animated a button inside of the block? That would be totally legal (since it would just call the UIView version which can animate anything), but very confusing.
I am making a custom keyboard and I have a function named setButtonConstraints(). When I insert this function into the viewDidLoad() and run my app the constraints are properly set. However when I move the function call into the override func updateViewConstraints() (which is supposed to be called after the subviews have been layed out) no constraints are set. What is the cause of this?
This is what the simple updateViewConstraints() looks like:
override func updateViewConstraints() {
super.updateViewConstraints()
// Add custom view sizing constraints here
setButtonConstraints()
}
Per Apple's documentation, updateViewConstraints() only gets called if the constraints need to be updated. Also, I believe you need to call the super.updateViewConstraints() after you change constraints.
The following link is helpful.
Where should I be setting autolayout constraints when creating views programmatically
Put your constraints code in updateViewConstraints and call this from viewWillAppear. The same method can also be called in response to rotation. The accepted answer is incorrect on both points it makes. Call super anywhere in the method. If you want to update the constraints call setNeedsUpdateConstraints which will handle it efficiently.
From the docs
You may override this method in a subclass in order to add constraints
to the view or its subviews. If you override this method, your
implementation must invoke super’s implementation.
And here.
I'm working on some custom UIView-based input controls, and I'm trying to ascertain proper practice for setting up the view. When working with a UIViewController, it's fairly simple to use the loadView and related viewWill, viewDid methods, but when subclassing a UIView, the closest methosds I have are `awakeFromNib, drawRect, and layoutSubviews. (I'm thinking in terms of setup and teardown callbacks.) In my case, I'm setting up my frame and internal views in layoutSubviews, but I'm not seeing anything onscreen.
What is the best way to ensure that my view has the correct height and width that I want it to have? (My question applies regardless of if I'm using autolayout, although there might be two answers.) What's the proper "best practice"?
Apple defined pretty clearly how to subclass UIView in the doc.
Check out the list below, especially take a look at initWithFrame: and layoutSubviews. The former is intended to setup the frame of your UIView whereas the latter is intended to setup the frame and the layout of its subviews.
Also remember that initWithFrame: is called only if you are instantiating your UIView programmatically. If you are loading it from a nib file (or a storyboard), initWithCoder: will be used. And in initWithCoder: the frame hasn't been calculated yet, so you cannot modify the frame you set up in Interface Builder. As suggested in this answer you may think of calling initWithFrame: from initWithCoder: in order to setup the frame.
Finally, if you load your UIView from a nib (or a storyboard), you also have the awakeFromNib opportunity to perform custom frame and layout initializations, since when awakeFromNib is called it's guaranteed that every view in the hierarchy has been unarchived and initialized.
From the doc of NSNibAwaking (now superseded by the doc of awakeFromNib):
Messages to other objects can be sent safely from within awakeFromNib—by which time it’s assured that all the objects are unarchived and initialized (though not necessarily awakened, of course)
It's also worth noting that with autolayout you shouldn't explicitly set the frame of your view. Instead you are supposed to specify a set of sufficient constraints, so that the frame is automatically calculated by the layout engine.
Straight from the documentation:
Methods to Override
Initialization
initWithFrame: It is recommended that you implement this method. You can also implement custom initialization methods in addition to,
or instead of, this method.
initWithCoder: Implement this method if you load your view from an Interface Builder nib file and your view requires custom
initialization.
layerClass Implement this method only if you want your view to use a different Core Animation layer for its backing store. For example,
if you are using OpenGL ES to do your drawing, you would want to
override this method and return the CAEAGLLayer class.
Drawing and printing
drawRect: Implement this method if your view draws custom content. If your view does not do any custom drawing, avoid overriding this
method.
drawRect:forViewPrintFormatter: Implement this method only if you want to draw your view’s content differently during printing.
Constraints
requiresConstraintBasedLayout Implement this class method if your view class requires constraints to work properly.
updateConstraints Implement this method if your view needs to create custom constraints between your subviews.
alignmentRectForFrame:, frameForAlignmentRect: Implement these methods to override how your views are aligned to other views.
Layout
sizeThatFits: Implement this method if you want your view to have a different default size than it normally would during resizing
operations. For example, you might use this method to prevent your
view from shrinking to the point where subviews cannot be displayed
correctly.
layoutSubviews Implement this method if you need more precise control over the layout of your subviews than either the constraint or
autoresizing behaviors provide.
didAddSubview:, willRemoveSubview: Implement these methods as needed to track the additions and removals of subviews.
willMoveToSuperview:, didMoveToSuperview Implement these methods as needed to track the movement of the current view in your view
hierarchy.
willMoveToWindow:, didMoveToWindow Implement these methods as needed to track the movement of your view to a different window.
Event Handling:
touchesBegan:withEvent:, touchesMoved:withEvent:, touchesEnded:withEvent:, touchesCancelled:withEvent: Implement
these methods if you need to handle touch events directly. (For
gesture-based input, use gesture recognizers.)
gestureRecognizerShouldBegin: Implement this method if your view handles touch events directly and might want to prevent attached
gesture recognizers from triggering additional actions.
This still comes up high in Google. Below is an updated example for swift.
The didLoad function lets you put all your custom initialization code. As others have mentioned, didLoad will be called when a view is created programmatically via init(frame:) or when the XIB deserializer merges a XIB template into your view via init(coder:)
Aside: layoutSubviews and updateConstraints are called multiple times for the majority of views. This is intended for advanced multi-pass layouts and adjustments when a view's bounds changes. Personally, I avoid multi-pass layouts when possible because they burn CPU cycles and make everything a headache. Additionally, I put constraint code in the initializers themselves as I rarely invalidate them.
import UIKit
class MyView: UIView {
//-----------------------------------------------------------------------------------------------------
//Constructors, Initializers, and UIView lifecycle
//-----------------------------------------------------------------------------------------------------
override init(frame: CGRect) {
super.init(frame: frame)
didLoad()
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
didLoad()
}
convenience init() {
self.init(frame: CGRectZero)
}
func didLoad() {
//Place your initialization code here
//I actually create & place constraints in here, instead of in
//updateConstraints
}
override func layoutSubviews() {
super.layoutSubviews()
//Custom manually positioning layout goes here (auto-layout pass has already run first pass)
}
override func updateConstraints() {
super.updateConstraints()
//Disable this if you are adding constraints manually
//or you're going to have a 'bad time'
//self.translatesAutoresizingMaskIntoConstraints = false
//Add custom constraint code here
}
}
There's a decent summary in the Apple documentation, and this is covered well in the free Stanford course available on iTunes. I present my TL;DR version here:
If your class mostly consists of subviews, the right place to allocate them is in the init methods. For views, there are two different init methods that could get called, depending on if your view is being instantiated from code or from a nib/storyboard. What I do is write my own setup method, and then call it from both the initWithFrame: and initWithCoder: methods.
If you're doing custom drawing, you indeed want to override drawRect: in your view. If your custom view is mostly a container for subviews, though, you probably won't need to do that.
Only override layoutSubViews if you want to do something like add or remove a subview depending on if you're in portrait or landscape orientation. Otherwise, you should be able to leave it alone.
layoutSubviews is meant to set frame on child views, not on the view itself.
For UIView, the designated constructor is typically initWithFrame:(CGRect)frame and you should set the frame there (or in initWithCoder:), possibly ignoring passed in frame value. You can also provide a different constructor and set the frame there.
I have several UITextViews in several ViewControllers. In the past, when I have a couple of instances of needing a custom drawing for a TextView or Label, etc I would just adjust the drawing in viewWillAppear inside the VC that owned the UI object. This time, I will be needed several instances to be customized.
Would it be more appropriate to just create a subclassed UITextView and include the drawing code in drawRect versus having the same drawing code spread around several VC's. I am mainly worried about performance. Code maintainability is a secondary concern though.
To be clear, this is what I would use in drawRect:
- (void)drawRect:(CGRect)rect {
self.layer.cornerRadius = 10;
self.clipsToBounds = YES;
}
So after further testing, initWithFrame doesn't get called, but initWithCoder does. I have also found that initWithCoder is called once and so is drawRect. In my use case (a StaticCellTableView with the UITextView in a cell, what would the difference be?
You can include those 2 lines in init or initWithCoder (In case it's a xib or storyboard) method of the subclassed UITextView.
Basically, this is just properties of the object - the don't need to run every time the UIView needs to refresh itself.
Create a ViewController baseclass, and then use that as the superclass for all your other VCs. You can then add this and other convenience methods to it and share the wealth so to speak.
In this particular case, putting it at the end of viewDidLoad would be a good place, as that is only messaged once, where viewWillAppear may be called multiple times. If you use viewdidLoad the code will be executed once.
I would not put those lines in the view's drawRect since that's called for every refresh. I'd recommend that you subclass UITextView and add those lines to the custom init method.
(iPhone SDK 3.x:) I have a UIControl subclass that creates a different number of subviews depending on the length of an NSArray property. Please take my word for it that this needs to be a UIControl rather than a UIView.
Currently I implement subview management in drawRect, beginning by removing all subviews and then creating the appropriate number based on the property. I don't think this is very good memory management and I'm not sure if drawRect is really the appropriate place to add subviews. Any thoughts on the best way to handle this pattern?
Thank you.
There is a method called layoutSubviews, and like the name already says, that method is thought to layout the subviews. You can call setNeedsLayout and the layoutSubviews method will be called (do not call layoutSubviews directly).