NSLayoutConstraint Contraints in code

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];