In reading the View Programming Guide from Apple it is apparent they have not updated it for constraints. So a couple of questions:
Many posts here talk about NOT using -initWithFrame when initializing a new UIView or setting it to CGRectZero or some equivalent. How would you handle this then?:
-(id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self){
//Set up rounded rectangle ivar
CGRect frame = [self bounds];
CGFloat radius = frame.size.height / 2;
_rectPath = [UIBezierPath bezierPathWithRoundedRect:frame cornerRadius:radius];
}
}
and then putting the drawing code in the drawRect:. I have found that it won't init properly without a frame. (Obviously, I'm initing this UIView and immediately setting constraints but no frame immediately). This code set's frame = (0,0,0,0) because constraints haven't been computed yet.
If we don't put this code in init where would we put it? Also, I thought it was good practice to init all our stuff we needed in the view in init.
So this leads to question...
When is -updateConstraints called in the runtime cycle and when does the view compute it's bounds using those constraints? I have noticed that the view really doesn't know what it's bounds are until after -layoutSubviews. Is there another place before this that the UIView knows it's bounds if it has only been set with constraints?
Sorry about all the questions, but they all kinda seem connected. Thanks for the looks.
Your problem with your frames is not related to auto layout. View size changes all the time. It is almost never the same as during object instantiation. You need to create/calculate the size of paths to fit the current size during drawRect, not when you first create the view.
The only objects you should set during init are properties and/or ivars that the rest of your class relies on existing in a certain state.
Related
The problem: Let's suppose I have an image and an element which constantly triggers viewDidLayoutSubviews (a scrollview.. so that at every scroll viewDidLayout would be called... or whatever element that triggers viewDidLayout quite often).
This image as well as the "viewDidLayout_element" are all set up well with autolayout in the storyboard.
Now:
I need to make the image to be a rounded one.
with the typical: layer.cornerRadius.. and layer.masksToBounds. This requires a calculated imageView frame.
In what view controller cycle do I make it programatically? Taking into consideration that:
*except for the viewDidLayoutSubviews I don't get the right frame
*the viewDidLayoutSubviews can be called even thousands of times depending on the "viewDidLayout_element" that triggers it.
*If I call layoutIfNeeded on the imageView in viewDidAppear (because it's the only case when frames are already available so we can force their calculation) the user will already catch a glimpse of the transformation from a square image to a circular image. In other words in viewDidAppear the frame becomes available for our manipulation, but is also available for milliseconds to the user's eyes.
*it does not make sense to fill the viewDidLayoutSubviews with flags (especially if there will be something more performance intensive than a circular imageView transformation) like below:
if !iDidChangedTheImage
{
imageView.applyCornerRadius()
}
The question:
Where do I have the correct frame size inside a viewController cycle without the problems from above? Or how do you usually solve this problem?
Subclass UIImageView to your custom class, and override layoutSubviews. After that you don't need to care about image view size change and updating corner radius, just use that class for your custom image view
#implementation CustomImageView
- (void)awakeFromNib {
[super awakeFromNib];
self.layer.masksToBounds = YES;
}
- (void)layoutSubviews {
[super layoutSubviews];
self.layer.cornerRadius = self.frame.size.height / 2.0;
}
#end
I'm initting a UIView with a xib, programatically:
- (id)initWithFrame:(CGRect)frame
{
self = [[[NSBundle mainBundle] loadNibNamed:#"MyViewNib" owner:self options:nil] objectAtIndex:0];
if (self)
{
//perform setup of various components
return self;
}
}
This view uses size classes for Any Width, Any Height, and Any Width, Compact Height.
I have a UIButton in a xib that I need to put a circle in the background of, like so:
self.closeButton.layer.cornerRadius = self.closeButton.frame.size.width / 2.0f;
self.closeButton.layer.backgroundColor = [UIColor colorWithWhite:164.0f / 255.0f alpha:1.0f].CGColor;
If I try setting the button's corner radius in the init function when I'm on a device using Any Width, Compact Height, the label's frame is still set to the Any Width, Any Height value. I've also tried overriding layoutSubviews and setting the value there, with no luck. It appears that the size class constraints are applied after layoutSubviews without another call to layoutSubviews, since the other components appear on-screen correctly.
So, I'm wondering if there's a good entry point for me to catch where the size classes are applied, so that I can set the background corner radius of the button correctly. I could just set the button up programmatically, but I'd like to figure out how to do this since it will probably come up again in the process of converting to size classes.
In your xib class -(void)awakeFromNib;
This works if I put it at the end of the init function:
[self performSelector:#selector(updateButtonBackground) withObject:nil afterDelay:.001];
Apparently by this point the constraints have been set up with the size classes. It's certainly non-ideal though, so if anyone has an answer that's event-driven or involves view "lifecycle" (as far as that applies to UIView) I'll accept that...
How about doing this?
-(void)layoutSubviews
{
[super layoutSubviews];
self.closeButton.layer.cornerRadius = self.closeButton.frame.size.width / 2.0f;
self.closeButton.layer.backgroundColor = [UIColor colorWithWhite:164.0f / 255.0f alpha:1.0f].CGColor;
//more of your changes
[self layoutIfNeeded]; // You can remove this line if it works without it for you..
}
I know this thread is old, but I see no good answer here.
Size classes are defined in traitCollectionDidChange: method. You can't ensure that traitCollection is set in initWithFrame: or awakeFromNib:.
So set your corner radius in traitCollectionDidChange: method based on the view size classes.
You need to apply the corner radius in viewDidLayoutSubviews. It is at this point that you know the bounds of the button have been established.
You can see an example on my blog.
I have created this simple custom UIView
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self) {
internalView = [UIView new];
[self addSubview:internalView];
internalView.backgroundColor = [UIColor whiteColor];
sublabel = [UILabel new];
sublabel.text = #"test";
sublabel.backgroundColor = [[UIColor yellowColor] colorWithAlphaComponent:0.4];
sublabel.textAlignment = NSTextAlignmentCenter;
sublabel.translatesAutoresizingMaskIntoConstraints = NO;
[internalView addSubview:sublabel];
}
return self;
}
- (void)layoutSubviews
{
[super layoutSubviews];
[internalView setFrame:self.bounds];
[sublabel setFrame:internalView.bounds];
}
#end
The view is used in a xib where are defined 4 constraints:
The constrains are related to the top, trailing, leading and the height.
The views hierarchy of the custom view is self -> internalView -> sublabel
The layoutSubviews is doing a simple thing like setting the frame of each subview with the bounds of the superview.
I created the code above just to point out a strange behaviour i found in translatesAutoresizingMaskIntoConstraints.
(The yellow view is the label)
If the value of the property is YES the results is what I expect from the code in the layoutSubviews method
If it is NO, with the same layoutSubviews i got:
The documentation of the translatesAutoresizingMaskIntoConstraints says:
If this is value is YES, the view’s superview looks at the view’s
autoresizing mask, produces constraints that implement it, and adds
those constraints to itself (the superview).
In both cases the autoresizingMask is set to UIViewAutoresizingNone and there are no constraints in the constraints property of the label.
Why with the translatesAutoresizingMaskIntoConstraints=NO the frame that i set in the layoutSubviews is not what i see on screen?
Edit 2:
I expect, given the exposed scenario, to have the same results with translatesAutoresizingMaskIntoConstraints set to YES or NO.
Edit:
I tried to swizzle the sizeToFit method to check if it is called. It's not.
This is happen in iOS6/7
Update 08/08/14
After further investigation i discovered that there is a way to change the frame of the label without having autolayout playing around.
I discovered that after the first pass of layout (when is called the layoutSubviews) with the translatesAutoresizingMaskIntoConstraints=NO autolayout adds constraints for the hugging/compression of the UILabel. The point is that for every view that implements intrinsicContentSize returning something different from UIViewNoIntrinsicMetric the autolayout adds specific constrains. That is the reason behind the resizing of the label.
So the first thing that i did is to reimplement a subclass of the UILabel to override the
intrinsicContentSize.
After that, following the suggestions in this really good article http://www.objc.io/issue-3/advanced-auto-layout-toolbox.html, I tried to turn of autolayout completely for the subviews involved removing [super layoutSubviews].
The goal for me was to avoid that autolayout could act on views where a was trying to apply animated transformations. So if you have the same needs i hope this can help you.
This comes more from intuition of having used it than actual study, but...
If you set translatesAutoresizingMaskIntoConstraints to YES, the system will create constraints to enforce the frame you defined for your view.
If it is set to NO, no constraints will be set for the view, and as you did not set them yourself either, the view will be resized according to default behaviours. In this case it seems to resize to the minimum content size because of the "contentHugging" values.
Bottom line is, from my understanding, when auto-layout is active all views need constraints to be properly placed. You either set that property to YES, or set the constraints yourself. If you don't do either, results will be a bit unpredictable.
The UIViewAutoresizingNone mask is still a valid mask, with fixed dimensions (no resizing) and it will be translated to constraints. Views can coexist without setting constraints, when you set that option to YES.
You are interpreting UIViewAutoresizingNone as meaning "no mask" when it really means "mask with no resizing". Sorry to disagree with you, but I think that this is the expected behaviour :)
I am working on my first project using Auto Layout and custom views. My question is this:
I created my custom view in Interface Builder then added constraints to stretch the view if needed which is working the way I want it to, however, consider the following code snippet from my custom view class -
// MyCustomView
-(id)initWithCoder:(NSCoder*)decoder
{
self = [super initWithCoder:decoder];
if(self != nil)
{
CGFloat layerWidth = self.bounds.size.width;
CGFloat layerHeight = self.bounds.size.height;
}
return self;
}
This code return the size set in IB. My drawing code relies on the new width and height (if the view has been stretched) but I don't know how to retrieve them.
First, that code is utterly silly because you are creating variables layerWidth and layerHeight and throwing them away, which is pointless.
Second, self.bounds.size is always the view's width and height. However, it is pointless to ask about this in initWithCoder:, which (as you have rightly seen) happens long before the view is put into the interface and even longer before the auto layout takes place that resizes it. If your drawing code relies on the bounds size, then retrieve the bounds size when you draw. If you need to draw again because the view has changed size, and if this is not happening all by itself, then implement layoutSubviews to tell the view that it needs to be drawn again.
I'm searching for a way to let a CALayer resize itself whenever its sublayers change (which means either when the bounds of any sublayer change or when the sublayer array itself changes).
When i worked with views before, i managed that through implementing sizeThatFits in my custom UIView subclass, which was called automatically by sizeToFit whenever the view's subviews changed.
Since CALayer has the sizeThatFits-equivalent-method preferredSize, i was surprised not to find a sizeToFit-equivalent.
I think you need to implement(override) the - (void)layoutSublayers
...
*Subclasses can override this to
* provide their own layout algorithm, which should set the frame of
* each sublayer
- (void)layoutSublayers
{
// self.frame = aNewSubLayer.bounds
// basically do algorithm for setting frame and bounds for this(self) layer and subLayers here
}