I set up width of UIView like this:
contentView.widthAnchor.constraint(equalToConstant: CGFloat(scrollWidth())).isActive = true
Now I want to change that width. The question is: how to remove old constraint and add new? I did create NSLayoutConstraint like this
scrollWidthConstraint = NSLayoutConstraint(
item: contentView,
attribute: .width,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 1.0,
constant: CGFloat(scrollWidth())
)
How to set that constraint for UIView for changing later?
First use this better and short and assign a reference to it
var widCon:NSLayoutConstraint!
widCon = contentView.widthAnchor.constraint(equalToConstant: CGFloat(scrollWidth()))
widCon.isActive = true
instead of NSLayoutConstraint(item: contentView, then Change it's constant
widCon.constant = ////
Related
I really need your help about this issue. I am creating a UIView object programatically without setting the bounds at the beggining. After creating I add constraints to that view in order to fit the required place in the screen.
But the problem is that, I want to use that UIView's bounds property in the following parts of the code but unfortunately I can not get the bounds after constraints sets as it shows on the screen.
Below I have sample code :
let previewView = UIView()
NSLayoutConstraint(item: previewView, attribute: .top, relatedBy: .equal, toItem: upperView, attribute: .bottom, multiplier: 1.0, constant: 0.0).isActive = true
NSLayoutConstraint(item: previewView, attribute: .bottom, relatedBy: .equal, toItem: self.view, attribute: .bottom, multiplier: 1.0, constant: 0.0).isActive = true
previewView.widthAnchor.constraint(equalToConstant: self.view.frame.width).isActive = true
previewView.translatesAutoresizingMaskIntoConstraints = false
print(previewView.bounds)
// (0.0, 0.0, 0.0, 0.0) ->>>> How can I get the bounds as it shows on the screen instead of 0,0,0,0
After this point, when I try to use, previewView.bounds property, it returns me its original size as 0.
How can I get the bounds as it shows on the screen with the related constaints' setup ?
Thank you very much Guys.
You can access it in
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
if once {
once = false
// process here
print(previewView.bounds)
}
}
but first declare the view as instance variable , make once = false in view
var previewView:UIView!
var once= true
see here
I'm trying to center multiple elements (labels and buttons) inside UIView (or UIStackView). I tried adding elements to UIStackView with Center Alignment and Distribution Fill and Spacing 10, but my elements keeps getting positioned from the left side. I tried changing centers. Still no luck.
What i'm trying to achieve:
[-------label--button-------] With 2 elements.
[--label--button--button--] With 3 elements.
Is there any way of achieving this without using spacers. Theoretically I maybe could use constrains, but i'm not sure it's a good idea because of changing number of elements.
let simpleView = UIView()
simpleView.addSubview(text)
simpleView.addSubview(button)
let leftLeading = NSLayoutConstraint(item: text, attribute:
.LeadingMargin, relatedBy: .Equal, toItem: simpleView,
attribute: .LeadingMargin, multiplier: 1.0,
constant: 10)
let leftLeading2 = NSLayoutConstraint(item: button, attribute:
.LeadingMargin, relatedBy: .Equal, toItem: simpleView,
attribute: .LeadingMargin, multiplier: 1.0,
constant: 10)
simpleView.addConstraint(leftLeading)
simpleView.addConstraint(leftLeading2)
simpleView.translatesAutoresizingMaskIntoConstraints = false
simpleView.sizeToFit()
newView.addSubview(simpleView)
let horizontalConstraint = NSLayoutConstraint(item: simpleView, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: newView, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0)
newView.addConstraint(horizontalConstraint)
let verticalConstraint = NSLayoutConstraint(item: simpleView, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: newView, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0)
newView.addConstraint(verticalConstraint)
I must be doing something wrong because this is what I get (newView is red, button is blue, text label is missing) :
Create a view, center the view where you need to. Then inside that view you can insert each element and give each one a programatic NSLayoutConstraint that has a .Leading of 5 or whatever spacing you want between elements.
VIEW[ELEMENT ELEMENT ELEMENT]
The number will not matter. Look into NSLayoutConstraints and make sure you use view.addConstraints.
I'm trying to make a view that will act as a sort of "panel", attached to the right side of the view controller.
That is, it is bound to the trailing, top, and bottom margins of the parent view controller, with a static width of 300
However, I just can't seem to get it right, I'm either breaking a constraint or doing something xcode tells me is illegal.
What am I doing wrong?
Here is the code in the controller
let myView = UIView()
view.backgroundColor = UIColor.redColor()
self.view.addSubview(view)
let topConstraint = NSLayoutConstraint(item: myView,
attribute: .Top,
relatedBy: .Equal,
toItem: self.topLayoutGuide,
attribute: .Bottom,
multiplier: 1,
constant: 0)
let trailingConstraint = NSLayoutConstraint(item: self.view,
attribute: .TrailingMargin,
relatedBy: .Equal,
toItem: myView,
attribute: .Trailing,
multiplier: 1,
constant: 0)
let bottomConstraint = NSLayoutConstraint(item: self.bottomLayoutGuide,
attribute: .Top,
relatedBy: .Equal,
toItem: myView,
attribute: .Bottom,
multiplier: 1,
constant: 0)
let widthConstraint = NSLayoutConstraint(item: myView,
attribute: .Width,
relatedBy: .Equal,
toItem: nil,
attribute: .NotAnAttribute,
multiplier: 1,
constant: 300)
self.view.addConstraints([trailingConstraint])
view.addConstraints([topConstraint, bottomConstraint, widthConstraint])
Actually the problem in your code is that you did not set the translatesAutoresizingMaskIntoConstraints of myview to false, whenever you want to use auto-layout constraints then you have to set translatesAutoresizingMaskIntoConstraints of a view to false.
Another Problem is that you do not add myview on self.view I have updated your code and Its working fine According your constraints.
Put below code in your ViewController .
let myView = UIView()
myView.backgroundColor = UIColor.redColor()
self.view.addSubview(myView)
myView.translatesAutoresizingMaskIntoConstraints = false
view.addConstraint(NSLayoutConstraint(item: myView, attribute: .Top, relatedBy: .Equal, toItem: self.topLayoutGuide, attribute: .Bottom, multiplier: 1, constant: 0))
view.addConstraint(NSLayoutConstraint(item: myView, attribute: .Bottom, relatedBy: .Equal, toItem: self.bottomLayoutGuide, attribute:.Top, multiplier: 1, constant: 20))
view.addConstraint(NSLayoutConstraint(item: myView, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute,multiplier: 1, constant: 300))
view.addConstraint(NSLayoutConstraint(item: myView, attribute: .TrailingMargin, relatedBy: .Equal, toItem: view, attribute: .TrailingMargin, multiplier: 1, constant: 0))
In your example code above, it seems like you are mixing up view and myView in a few places. In any event, widthConstraint should be added to myView and topConstraint, trailingConstraint, and bottomConstraint should be added to self.view. The reason for this is constraints must be added to the closest superview ancestor that lays out both views involved in the constraint. In the case where you are constraining a child view attribute to an attribute on its parent view, the constraint must be added to the parent view, since it lays out both itself and the child view. If you have a constraint between two sibling views, the constraint would be added to their parent view, since it is the closest ancestor that lays out both the views involved.
If you're able to target iOS 9.0 and above, it's much cleaner and easier to use the new NSLayoutAnchor and NSLayoutDimension API for creating these kinds of constraints. It also provides strict type checking and the compiler can verify correctness. With these new APIs, your example code would simply become:
let myView = UIView()
myView.backgroundColor = UIColor.redColor()
self.view.addSubview(myView)
let margins = self.view.layoutMarginsGuide
myView.trailingAnchor.constraintEqualToAnchor(margins.trailingAnchor).active = true
myView.topAnchor.constraintEqualToAnchor(margins.topAnchor).active = true
myView.bottomAnchor.constraintEqualToAnchor(margins.bottomAnchor).active = true
myView.widthAnchor.constraintEqualToConstant(300.0).active = true
No need to explicitly add the constraints to the right view, etc. You can read more about this method of creating constraints here:
https://developer.apple.com/library/ios/documentation/AppKit/Reference/NSLayoutAnchor_ClassReference/
and here:
https://developer.apple.com/library/ios/documentation/AppKit/Reference/NSLayoutDimension_ClassReference/
There seems to be some ambiguity in your code, you are creating a UIView as myView but adding view to self.view and even constraint also to view itself. So correct your code and replace view with myView.
Secondly setTranslayesAutoresizingMaskIntoConstraints to false.
Then add all the constraints to self.view. This should solve your problem.
myView.setTranslatesAutoresizingMaskIntoConstraints(false)
self.view.addConstraints([trailingConstraint, bottomConstraint, widthConstraint])
VFL is also a better and clean approach. It actually gives a visualization of how constraint are setup.
I am not sure what I am missing here, I have been going at this for hours, looks at constant tutorials, and I am still getting an issue with conflicting constraints. Basically I have a button, and on this button I want to add a new view that is center to the button and the same size. When I go to apply the constraints, it is telling me that there are conflicting constraints, and I am just not understanding what can be conflicting here.
//Create a new view
let selectBorderView = UIView();
//Guarantee there are no constraints attached to it
NSLayoutConstraint.deactivateConstraints(selectBorderView.constraints);
//Add the new view to the button
sender.addSubview(selectBorderView);
//Create constraint selectBorderView.width = button.width
let constraintEW = NSLayoutConstraint(item: selectBorderView, attribute: .Width, relatedBy: .Equal, toItem: selectBorderView.superview, attribute: .Width, multiplier: 1, constant: 0);
//Create constraint selectBorderView.height = button.height
let constraintEH = NSLayoutConstraint(item: selectBorderView, attribute: .Height, relatedBy: .Equal, toItem: selectBorderView.superview, attribute: .Height, multiplier: 1, constant: 0);
//Create constraint selectBorderView.centerX = button.centerX
let constraintCX = NSLayoutConstraint(item: selectBorderView, attribute: .CenterX, relatedBy: .Equal, toItem: selectBorderView.superview!, attribute: .CenterX, multiplier: 1, constant: 0);
//Create constraint selectBorderView.centerY = button.centerY
let constraintCY = NSLayoutConstraint(item: selectBorderView, attribute: .CenterY, relatedBy: .Equal, toItem: selectBorderView.superview, attribute: .CenterY, multiplier: 1, constant: 0);
//add the constraints to the button
selectBorderView.superview!.addConstraint(constraintEW);
selectBorderView.superview!.addConstraint(constraintEH);
selectBorderView.superview!.addConstraint(constraintCX);
selectBorderView.superview!.addConstraint(constraintCY);
You are likely seeing an error message that says something like:
Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)
If you see that warning, you should set translatesAutoresizingMaskIntoConstraints to false:
selectBorderView.translatesAutoresizingMaskIntoConstraints = false
I have a UISegmentedControl defined programmatically.
I am trying to add a layout constraint so that when my iPad rotates, the segmented control sizes correctly within the rotated view rather than spill off screen.
I apply the following constraint:
streamSegmentedControl.translatesAutoresizingMaskIntoConstraints = false
let segmentedControlWidth = NSLayoutConstraint(item: streamSegmentedControl,
attribute: .Width,
relatedBy: .Equal,
toItem: self.containerView,
attribute: .Width,
multiplier: 1.0,
constant: -10.0)
containerView.addConstraint(segmentedControlWidth)
My UIsegmentControl is defined as follows:
streamSegmentedControl = UISegmentedControl(items: ["Today's Events", "Past Events"])
streamSegmentedControl.frame = CGRectMake(-10,containerView.frame.size.height*0.3,containerView.frame.width+20,40)
streamSegmentedControl.selectedSegmentIndex = 0
streamScope = "today"
streamSegmentedControl.setTitleTextAttributes(segmentedControlFont as [NSObject : AnyObject], forState: .Normal)
streamSegmentedControl.backgroundColor = UIColor.colorFromClass("background")
streamSegmentedControl.tintColor = UIColor.colorFromClass("default")
streamSegmentedControl.addTarget(self, action: "changeStreamScope:", forControlEvents: UIControlEvents.ValueChanged)
containerView.addSubview(streamTableView)
containerView.addSubview(streamSegmentedControl)
I don't get an error, but at runtime, my segmented control disappears. Not sure what I am missing here as I've only done auto layout within storyboards in the past.
I only want to be able to adjust the width of the segmented control, so I assume I only need a single layout constraint.
Can anyone give me some direction? Thanks.
You need to add three constraints at least. Leading, top and trailing.
I am weak in swift but your constraints should look like.
let segmentedControlTop = NSLayoutConstraint(item: streamSegmentedControl,
attribute: .Top,
relatedBy: .Equal,
toItem: self.containerView,
attribute: .Top,
multiplier: 1.0,
constant: 0.0)
let segmentedControlLeading = NSLayoutConstraint(item: streamSegmentedControl,
attribute: .Leading,
relatedBy: .Equal,
toItem: self.containerView,
attribute: .Leading,
multiplier: 1.0,
constant: 0.0)
let segmentedControlTrailing = NSLayoutConstraint(item: streamSegmentedControl,
attribute: .Trailing,
relatedBy: .Equal,
toItem: self.containerView,
attribute: .Trailing,
multiplier: 1.0,
constant: 0.0)
containerView.addConstraint(segmentedControlTop)
containerView.addConstraint(segmentedControlLeading)
containerView.addConstraint(segmentedControlTrailing)
If you want to keep a 5 point offset from superview, try playing with constant values of leading and trailing using 5 points.