I have set constraints on Storyboard, and tried to center CollectionView horizontally and give an extra offset.
I tried logging constraints on console by using this and consoled all the constraints.
print(collectionView.constraints)
How can I overwrite 30 offset to 50 offset (for example) programmatically?
Create an IBOutlet to the constraint you wish to overwrite.
#IBOutlet weak var collectionViewCenterXConstraint: NSLayoutConstraint!
then whenever you want to change it.
collectionViewCenterXConstraint.constant = 50 // the offset will be 50 now.
Related
I have tableView cell with different content(views, labels, imageViews) in one cell. But in something cells content can be not full. How can i use resizing cells without removing and adding always constraints? Thanks.
One of possible solutions for this problem:
Add constraints for hidden state with priority 1000
Add extra constraints for resized state with lower priority (ex 750)
Save constraints that is ONLY for hidden state into IBOutlet collection
Save constraints that is ONLY for resized state into another IBOutlet collection
Code:
#IBOutlet var hiddenConstraints: [NSLayoutConstraint] = []
#IBOutlet var visibleConstraints: [NSLayoutConstraint] = []
func hide(_ hide: Bool) {
for hiddenConstraint in self.hiddenConstraints {
hiddenConstraint.isActive = hide
}
for visibleConstraint in self.visibleConstraints {
visibleConstraint.isActive = !hide
}
self.layoutIfNeeded()
}
There is faster solution:
Move content that can be hidden into container view
Set height constraint for container view
Change from code height constraint constant to 0 if hidden or to proper height if visible
Code:
#IBOutlet var heightConstraint: NSLayoutConstraint!
func hide(_ hide: Bool) {
self. heightConstraint.constant = hide ? 0 : 150 //Estimated height
self.layoutIfNeeded()
}
This is not a good approach, as it will lead to constraint crashes at runtime. So I prefer to use first one.
Also you will need to update your cell from table to move other cells up or down.
Ray Wenderlich has a fantastic tutorial on dynamic sizing of table cells that can be found here:
https://www.raywenderlich.com/129059/self-sizing-table-view-cells
TL;DR You need to make sure your cell's content is pinned on all four sides to the cell's content view, as well as setting as high priority vertical hugging, greater than or equal to height constraint on your label.
In my application I have added a UIButton with following constraints:
Leading space = 10
Trailing space = 10
Height = 50
Bottom space =10
By this I got a button placed at a bottom of device. It works good on single device(iPhone 4), but as device height increases button height remains same(iPhone 6).
I want to change button height also with Autolayout.
I tried some example which suggest to add multiplier value but no luck.
I am using Xcode-8 with Swift3
Please suggest me.
There is multiple way to handle this issue
First:-
Create 1,Give Fixed Height Constraint to button
2.Create #IBOutlet of Height Constraint
like this way
#IBOutlet weak var btnHeightConstraint: NSLayoutConstraint!
3. Set Constraint constant as per your requirement
like this way.
btnHeightConstraint.constant = 50 //your button height 50
btnHeightConstraint.constant = 60 //your button height 60
Set all the constarints which is needed and set 'Equal Height' constraint with your 'superview' and set the multiplier value i.e if your view size is same as iphone 5 then set multiplier value as 'yourHeight:568', you will get required output.
I am using UICollectionView and in it my cells have auto width based on the content(text size) e.g. first row might contain 8 items and 2nd row might contains only 1. This is working fine.
I want to set the height of my UICollectionView to show all the available items but not more(not the empty space at the bottom...). If I use auto layout than I have to set the height or bottom align constraint.
But in this way the height will be fixed. Is there any way I can get number of rows in and calculate height dynamically?
Here is what my story board look like:
You could use fixed height constraint at design time and than change it at runtime when deferred height value calculated. Height constraint need to be referenced in code and than needs to be changed with your calculated height.
// Height constraint of collection view
#IBOutlet weak var heightContstraint: NSLayoutConstraint!
override func viewDidLoad() {
super.viewDidLoad()
setHeightOfCollectionView()
}
func setHeightOfCollectionView() {
// Calculate height of collection view depending on collection item count
let calculatedHeight:CGFloat = 500.0
heightContstraint.constant = calculatedHeight
}
You should check the images below that demonstrate how to do.
Hope it would help.
Suppose I have three labels that are laid out below each other in a column. The uppermost label's top edge is pinned to the superview's top edge. All following labels' top edges are pinned to the preceding label's bottom edge. The leading and trailing edges of all labels are pinned to the leading and trailing edge of the superview. Here's what it looks like in Interface Builder (I added a blue background on every label to visualize its extent).
In the simulator the result looks like this.
All labels are connected to outlets in a view controller.
#IBOutlet weak var label1: UILabel!
#IBOutlet weak var label2: UILabel!
#IBOutlet weak var label3: UILabel!
When I set the text of label2 to nil
label2.text = nil
the label itself collapses.
However, the top and bottom spaces around the label do not collapse. This is evident by the fact that there is no blue background on the middle label in the last screenshot. As a result, the space between label1 and label3 is double the space of the layout in the first screenshot.
My question is - on iOS8 - what is the easiest way to collapse either the middle label's top or bottom space so that the two remaining labels still use the vertical spacing defined in the original layout? To be clear, this is the result I want to achieve.
Options I've found so far:
Bottom/Top Spacing Constraint Outlet
Define an outlet for the middle label's top or bottom spacing constraint.
#IBOutlet weak var spacingConstraint: NSLayoutConstraint!
Store the constraint's initial constant into a variable (e.g. in awakeFromNib or viewDidLoad).
private var initialSpacing: CGFloat!
override func viewDidLoad() {
initialSpacing = spacingConstraint.constant
...
Set the constraint's constant to zero whenever the text is set to nil or back to its initial value when the text is not nil.
spacingConstraint.constant = label2.text == nil ? 0 : initialSpacing
This approach feels a bit clumsy since it requires two additional variables.
Height Constraint Outlet
Set the vertical spacing around the middle label to zero and increase its height by the same amount. Define an outlet for the height constraint and proceed as above, setting the height to zero when the text is nil and back to it's initial value when the height is not nil.
This is still as clumsy as the previous approach. In addition, you have to hardcode the spacing and cannot use the built-in default spacings (blank fields in Interface builder).
UIStackView
This is not an option since UIStackView is only available on iOS 9 and above.
I'm using this UIView category for this purpose.
It extends UIView by adding two more property named fd_collapsed and fd_collapsibleConstraints using objective-c runtime framework. You simply drag constraints that you want to be disabled when fd_collapsed property set to YES. Behind the scene, it captures the initial value of these constraints, then set to zero whenever fd_collapsed is YES. Reset to initial values when fd_collapsed is NO.
There is also another property called fd_autocollapsed
Not every view needs to add a width or height constraint, views like UILabel, UIImageView have their Intrinsic content size when they have content in it. For these views, we provide a Auto collapse property, when its content is gone, selected constraints will collapse automatically.
This property automatically sets fd_collapsed property to YES whenever specified view has content to display.
It's really simple to use. It's kinda shame that there is no builtin solution like that.
Your solutions are good enough for me and I'd do Bottom/Top Spacing Constraint Outlet solution but since you want something different. You can use this third party: https://github.com/orta/ORStackView It has iOS7+ support and do exactly what you need.
This is low-key a pain all perfectionist devs learn about when trying to stack a bunch of labels. Solutions can get too verbose, annoying to folow, and really annoying to implement (ie. keeping a reference to the top constraint... gets annoying once you do it multiple times, or just change the order of the labels)
Hopefully my code below puts an end to this:
class MyLabel: UILabel {
var topPadding: CGFloat = 0
override func drawText(in rect: CGRect) {
var newRect = rect
newRect.origin.y += topPadding/2
super.drawText(in: newRect)
}
override var intrinsicContentSize: CGSize {
var newIntrisicSize = super.intrinsicContentSize
guard newIntrisicSize != .zero else {
return .zero
}
newIntrisicSize.height += topPadding
return newIntrisicSize
}
}
Usage:
let label = MyLabel()
label.topPadding = 10
// then use autolayout to stack your labels with 0 offset
Granted, its only for top padding, but that should be the only thing you need to layout your labels properly. It works great with or without autolayout. Also its a big plus not needing to do any extra mental gymnastics just to do something so simple. Enjoy!
I have a circle in the centre of a screen with a margin constraint of 50 on either end. Hence, the width of the circle is dependent on the screen size.
So, what I tried was this:
Approach 1
I set up the margins in the storyboard to define the circle width (50 on left and right)
Then I used the following code:
#IBOutlet weak var helpButHeight: NSLayoutConstraint!
#IBOutlet weak var helpBut: UIButton!
ViewDidLoad:
helpButHeight.constant = helpBut.frame.size.width
This didn't work.
Since the screen width is 400, and the margin is 50 on either end, then helpBut.frame.size.width should have given me 300.
Instead it gave me 46.
Approach 2
This was my work-around:
ViewDidLoad:
let screenSize: CGRect = UIScreen.mainScreen().bounds
helpButHeight.constant = screenSize.width - 100
because 100 = 50 + 50, the two margins.
Works fine !
Question
Why did I have to do this? Why did the first approach not work? Why 46 and not 300?
The reason is that constraints haven't kicked in, in the viewDidLoad function. The lifecycle looks something like
viewDidLoad -- Constraints haven't set
viewWillAppear -- Constraints haven't set
viewWillLayoutSubviews -- Constraints are setting
viewDidLayoutSubviews -- Constraints are set
viewDidAppear -- Constraints are set
If you want any view to be in center just put the horizontal/vertical center constraint...No code required.. If you want to have padding just put the left and right constraints...Just to remind you don't use both of them together...It'll break...