139
votes

have been getting into autolayouts recently and I'm stuck on what seems like a really trivial problem example. I have a view that I want to sit at the top of the screen, and take up half of the screen-height. Simple before autolayout - just tack it in place and tell it to expand vertically when the superview resizes.

Now, I can't for the life of me see how to do it. Here's what I get when I try to set this up:

autolayout blues

The bottom space constraint is set to "equals 284", which is absolute and absolutely useless to me when I change to iPhone4 layout, as it keeps 284 points space at the bottom of the screen, and shrinks the view to no longer be half the size of the screen. And there's no way of setting that constraint to equal some fraction of any other view's height..

After struggling for a while, the only way I can think of doing this would be to introduce another view below this view, pin their heights equally, have them sit above and below each other and then set the second (bottom) view to be invisible.. which seems a bit ugly!

Am I missing something obvious?..

6
I don't think it is ugly, but a smart trick to get what you want using IB. I have done this, and when you use proper element names, you can make clear what is going on. You can even have a third element on a different position, or centers, change size based on these two subviews.Jelle

6 Answers

174
votes

This is now possible in IB as of [at least] Xcode 5.1.1. Although it took me sometime to figure out it is actually super simple:

First create a basic top alignment constraint (you will also need to setup bottom, left, and right constraints, like normal) . Then select the constraint and navigate to the Attribute inspector:

Demonstration of steps above

Then you can adjust the multiplier. If you want it 50% of the super view leave it at 1, since it is aligned per the super's center. This is also a great way to create views that are other percentages too (like 25% of super view)

Demonstration of second step above

191
votes

Storyboard solution where you can set exact ratio between any views:

Set height equality constraint

Now:

Edit constraint's multiplier

PROFIT!!!

Result

P.S. Also note that this method works with views on different nesting levels and (obviously) applicable for width

P.P.S. sometimes it might be helpful to "reverse first and second item" of constraint or set reverse multiplier (for example 2 instead of 0.5) (but these methods are not helpful if you don't understand how views relate between each other).

31
votes

After a bit more time I've come up with the following.

I'm noting it as an answer but it's not very satisfying, since it assumes you can't actually do this in Interface Builder, but the correct constraint can be added in code afterwards as:

- (void) viewWillAppear:(BOOL)animated
{

    NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:upperview
                                                                 attribute:NSLayoutAttributeHeight 
                                                                 relatedBy:0 
                                                                    toItem:self.view
                                                                 attribute:NSLayoutAttributeHeight
                                                                multiplier:.5 
                                                                  constant:0];
    [self.view addConstraint:constraint];

}

Basically, it sets a multiplier of 0.5 against the height of self.view, acting on upperview. I had to set the priority of the bottom vertical space constraint in IB to lower than 1000 to avoid a bunch of runtime messages about breaking constraints as well.

So if anyone can show how to do this in Interface Builder, that would better answer my question, otherwise I guess this is as good as it gets (for now)???

10
votes

Slightly easier and more straight forward than method than Fyodor Volchyok's answer. -Hold down the control button and click on the subview. -Still holding down on the command button, drag cursor to the superview then click on the superview. -Select "Aspect Ratio".

enter image description here

-Then click the Size Inspector. -Then double click on the constraint. enter image description here

-Make sure that "height" is selected for both items. enter image description here

-Then change the "Multiplier" to 0.5 for half the screen, or whatever fraction of the superview you desire. enter image description here

7
votes

There i also another possibility in code in case you have 2 views that should both have the same height: just set the height of view2 to the height of view1 (the trick here is not setting the height of view1 explicitely).

    [self.view addConstraints:[NSLayoutConstraint
        constraintsWithVisualFormat:@"V:[topLayoutGuide]-0-[_view1]-0-[_view2(==_view1)]-0-[bottomLayoutGuide]"
                            options:0
                            metrics:nil
                              views:viewsDict]];
0
votes

Swift version of Mete's answer:

    override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.



    upperView.translatesAutoresizingMaskIntoConstraints = false


    var constraint = NSLayoutConstraint(item: upperView,
                                        attribute: NSLayoutAttribute.top,
                                        relatedBy: NSLayoutRelation.equal,
                                        toItem: self.view,
                                        attribute: NSLayoutAttribute.top,
                                        multiplier: 1,
                                        constant: 0)

    self.view.addConstraint(constraint)


    constraint = NSLayoutConstraint(item: upperView,
                                    attribute: NSLayoutAttribute.height,
                                    relatedBy: NSLayoutRelation.equal,
                                    toItem: self.view,
                                    attribute: NSLayoutAttribute.height,
                                    multiplier: 0.5,
                                    constant: 0)

    self.view.addConstraint(constraint)


    constraint = NSLayoutConstraint(item: upperView,
                                    attribute: NSLayoutAttribute.leading,
                                    relatedBy: NSLayoutRelation.equal,
                                    toItem: self.view,
                                    attribute: NSLayoutAttribute.leading,
                                    multiplier: 1,
                                    constant: 0)

    self.view.addConstraint(constraint)


    constraint = NSLayoutConstraint(item: upperView,
                                    attribute: NSLayoutAttribute.trailing,
                                    relatedBy: NSLayoutRelation.equal,
                                    toItem: self.view,
                                    attribute: NSLayoutAttribute.trailing,
                                    multiplier: 1,
                                    constant: 0)

    self.view.addConstraint(constraint)


}