CODEWITHSUNDEEP
iosobjective-cconstraints
Saint Robson
Saint Robson

Reputation: 5525

How do constraints work programmatically?

I'm trying to learn how constraints work programmatically for iOS apps, by making a simple project (single view application) shown below:

enter image description here

I succeeded in creating the top space only using this code in viewDidLoad:

NSLayoutConstraint *myConstraint =[NSLayoutConstraint
                                   constraintWithItem:_container
                                   attribute:NSLayoutAttributeTop
                                   relatedBy:NSLayoutRelationEqual
                                   toItem:self.view
                                   attribute:NSLayoutAttributeTop
                                   multiplier:1.0
                                   constant:200];

[self.view addConstraint:myConstraint];

myConstraint =[NSLayoutConstraint
               constraintWithItem:_container
               attribute:NSLayoutAttributeHeight
               relatedBy:NSLayoutRelationEqual
               toItem:nil
               attribute:NSLayoutAttributeNotAnAttribute
               multiplier:1.0
               constant:216];

[_container addConstraint:myConstraint];

but I failed to set the height of _container (UIView - subview of superview). How would I create multiple constraints in a case like this? Thank you.

UPDATE : I will manipulate the size of top-space programmatically so the _container will move up and down, or even offscreen.

Upvotes: 2

Views: 1956

Answers (1)

jrturton
jrturton

Reputation: 119272

You can set a height constraint in code using visual format language : "V:[view(==216.0)]" or by using constraintWithItem: where the second item is nil, the second attribute is NSLayoutAttributeNotAnAttribute and the constant value is your height.

Upvotes: 3

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