I have a UIView inside a UIViewm and I want the inner UIView to be always centered inside the outer one, without it having to resize the width and height.
I've set the struts and springs so that it's on top/left/right/bottom without setting the resize. But it still doesn't center. Any idea?
Before we'll begin, let's just remind that origin point is the Upper Left corner CGPoint of a view.
An important thing to understand about views and parents.
Lets take a look at this simple code, a view controller that adds to it's view a black square:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
createDummyView()
super.view.backgroundColor = UIColor.cyanColor();
}
func createDummyView(){
var subView = UIView(frame: CGRect(x: 15, y: 50, width: 50 , height: 50));
super.view.addSubview(subView);
view.backgroundColor = UIColor.blackColor()
}
}
This will create this view: the black rectangle origin and center does fit the same coordinates as it's parent
Now let's try to add subView another SubSubView, and giving subSubview same origin as subView, but make subSubView a child view of subView
We'll add this code:
var subSubView = UIView();
subSubView.frame.origin = subView.frame.origin;
subSubView.frame.size = CGSizeMake(20, 20);
subSubView.backgroundColor = UIColor.purpleColor()
subView.addSubview(subSubView)
And this is the result:
Because of this line:
subSubView.frame.origin = subView.frame.origin;
You expect for the purple rectangle's origin to be same as it's parent (the black rectangle) but it goes under it, and why is that? Because when you add a view to another view, the subView frame "world" is now it's parent BOUND RECTANGLE, if you have a view that it's origin on the main screen is at coords (15,15) for all it's sub views, the upper left corner will be (0,0)
This is why you need to always refer to a parent by it's bound rectangle, which is the "world" of it's subViews, lets fix this line to:
subSubView.frame.origin = subView.bounds.origin;
And see the magic, the subSubview is now located exactly in it's parent origin:
So, you like "ok I only wanted to center my view by my parents view, what's the big deal?" well, it isn't big deal, you just need to "translate" the parent Center point which is taken from it's frame to parent's bounds center by doing this:
subSubView.center = subView.convertPoint(subView.center, fromView: subSubView);
You're actually telling him "take parents view center, and convert it into subSubView world".
And you'll get this result:
First of all disable child views autoresizing
UIView *view1, *view2;
[childview setTranslatesAutoresizingMaskIntoConstraints:NO];
If you are UIView+Autolayout or Purelayout:
[view1 autoAlignAxis:ALAxisHorizontal toSameAxisOfView:view2];
[view1 autoAlignAxis:ALAxisVertical toSameAxisOfView:view2];
If you are using only UIKit level autolayout methods:
[view1 addConstraints:({
@[ [NSLayoutConstraint
constraintWithItem:view1
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:view2
attribute:NSLayoutAttributeCenterX
multiplier:1.f constant:0.f],
[NSLayoutConstraint
constraintWithItem:view1
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:view2
attribute:NSLayoutAttributeCenterY
multiplier:1.f constant:0.f] ];
})];
I prefer:
UIView *parentView, *childView;
[childView setFrame:({
CGRect frame = childView.frame;
frame.origin.x = (parentView.frame.size.width - frame.size.width) / 2.0;
frame.origin.y = (parentView.frame.size.height - frame.size.height) / 2.0;
CGRectIntegral(frame);
})];
With IOS9 you can use the layout anchor API.
The code would look like this:
childview.centerXAnchor.constraintEqualToAnchor(parentView.centerXAnchor).active = true
childview.centerYAnchor.constraintEqualToAnchor(parentView.centerYAnchor).active = true
The advantage of this over CGPointMake or CGRect is that with those methods you are setting the center of the view to a constant but with this technique you are setting a relationship between the two views that will hold forever, no matter how the parentview changes.
Just be sure before you do this to do:
self.view.addSubview(parentView)
self.view.addSubView(chidview)
and to set the translatesAutoresizingMaskIntoConstraints for each view to false.
This will prevent crashing and AutoLayout from interfering.
Another solution with PureLayout using autoCenterInSuperview.
// ...
UIView *innerView = [UIView newAutoLayoutView];
innerView.backgroundColor = [UIColor greenColor];
[innerView autoSetDimensionsToSize:CGSizeMake(100, 30)];
[outerview addSubview:innerView];
[innerView autoCenterInSuperview];
This is it how it looks like:
func callAlertView() {
UIView.animate(withDuration: 0, animations: {
let H = self.view.frame.height * 0.4
let W = self.view.frame.width * 0.9
let X = self.view.bounds.midX - (W/2)
let Y = self.view.bounds.midY - (H/2)
self.alertView.frame = CGRect(x:X, y: Y, width: W, height: H)
self.alertView.layer.borderWidth = 1
self.alertView.layer.borderColor = UIColor.red.cgColor
self.alertView.layer.cornerRadius = 16
self.alertView.layer.masksToBounds = true
self.view.addSubview(self.alertView)
})
}// calculation works adjust H and W according to your requirement
