iOS Auto Layout NSLayoutConstraint: Contraints in code!
Example
When we are working on a framework, if the constraints are not too complex, we'd better use Interface Builder or NSLayoutConstraint in code to make it smaller enough, instead of import Masonry or SnapKit.
for example:
- Objective-C
// 1. create views
UIView *blueView = [[UIView alloc] init];
blueView.backgroundColor = [UIColor blueColor];
[self.view addSubview:blueView];
UIView *redView = [[UIView alloc] init];
redView.backgroundColor = [UIColor redColor];
[self.view addSubview:redView];
// 2. forbid Autoresizing
blueView.translatesAutoresizingMaskIntoConstraints = NO;
redView.translatesAutoresizingMaskIntoConstraints = NO;
// 3. make contraints
// 3.1 blueView
NSLayoutConstraint *blueLeft = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1 constant:20];
[self.view addConstraint:blueLeft];
NSLayoutConstraint *blueTop = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1 constant:20];
[self.view addConstraint:blueTop];
NSLayoutConstraint *blueRight = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1 constant:-20];
[self.view addConstraint:blueRight];
NSLayoutConstraint *blueHeight = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1 constant:50];
[self.view addConstraint:blueHeight];
// 3.2 redView
NSLayoutConstraint *redTop = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeBottom multiplier:1 constant:20];
[self.view addConstraint:redTop];
NSLayoutConstraint *redRight = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1 constant:-20];
[self.view addConstraint:redRight];
NSLayoutConstraint *redHeight = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeHeight multiplier:1 constant:0];
[self.view addConstraint:redHeight];
NSLayoutConstraint *redWidth = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeWidth multiplier:0.5 constant:0];
[self.view addConstraint:redWidth];
