Adding constraints programmatically in Objective-C

I'll get the ball rolling for you so you can see the general idea, otherwise use the documentation as provided by Larme.

Add the constraint in your superview (probably your view controller).

NSLayoutConstraint *centreHorizontallyConstraint = [NSLayoutConstraint                                      constraintWithItem:self.uiButton                                      attribute:NSLayoutAttributeCenterX                                      relatedBy:NSLayoutRelationEqual                                      toItem:self.view                                      attribute:NSLayoutAttributeCenterX                                      multiplier:1.0                                      constant:0];[self.view addConstraint:centreHorizontallyConstraint];

So as you can see we are saying constraint the centre x attribute of UIButton too the centre x attribute of the View Controllers view with no additional offsets (multiplier set to 1.0 and constant 0).

Make sure you add it to your view controller's view not the button because the button has not been laid out at this point and therefore you cannot add a constraint to it! (Please someone correct me if I'm wrong here). I add my constraints in the viewDidLoad method.

We have better option available from iOS 9+

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectZero];imageView.translatesAutoresizingMaskIntoConstraints = false;[self.view addSubview:imageView];[imageView.widthAnchor constraintEqualToConstant:imageSize.width].active = YES;[imageView.heightAnchor constraintEqualToConstant:imageSize.height].active = YES;[imageView.centerXAnchor constraintEqualToAnchor:self.view.centerXAnchor].active = YES;[imageView.topAnchor constraintEqualToAnchor:self.view.topAnchor constant:25].active = YES;

Swift 4

var imageView = UIImageView(frame: CGRect.zero)imageView.translatesAutoresizingMaskIntoConstraints = falseview.addSubview(imageView)imageView.widthAnchor.constraint(equalToConstant: imageSize.width).isActive = trueimageView.heightAnchor.constraint(equalToConstant: imageSize.height).isActive = trueimageView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = trueimageView.topAnchor.constraint(equalTo: view.topAnchor, constant: 25).isActive = true// OR you can use: NSLayoutConstraint.activate([NSLayoutConstraint]) to activate all at once.

NB: Always add constrains after added the view to view hierarchy.

I found this tutorial best.

http://www.tutorialspoint.com/ios/ios_auto_layouts.htm

My requirement was to set:

• Leading Space
• Top Space
• fixed Width
• fixed Height

Adding NSLayoutConstraint with the code below I was able to achieve it

Objective-c

self.btnCoin.translatesAutoresizingMaskIntoConstraints = NO;/* Leading space to superview */NSLayoutConstraint *leftButtonXConstraint = [NSLayoutConstraint                                             constraintWithItem:self.btnCoin attribute:NSLayoutAttributeLeft                                             relatedBy:NSLayoutRelationEqual toItem:self attribute:                                             NSLayoutAttributeLeft multiplier:1.0 constant:30];/* Top space to superview Y*/NSLayoutConstraint *leftButtonYConstraint = [NSLayoutConstraint                                             constraintWithItem:self.btnCoin attribute:NSLayoutAttributeTop                                             relatedBy:NSLayoutRelationEqual toItem:self attribute:                                             NSLayoutAttributeTop multiplier:1.0f constant:258];/* Fixed width */NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem:self.btnCoin                                                                   attribute:NSLayoutAttributeWidth                                                                   relatedBy:NSLayoutRelationEqual                                                                      toItem:nil                                                                   attribute:NSLayoutAttributeNotAnAttribute                                                                  multiplier:1.0                                                                    constant:35];/* Fixed Height */NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:self.btnCoin                                                                    attribute:NSLayoutAttributeHeight                                                                    relatedBy:NSLayoutRelationEqual                                                                       toItem:nil                                                                    attribute:NSLayoutAttributeNotAnAttribute                                                                   multiplier:1.0                                                                     constant:12];/* 4. Add the constraints to button's superview*/[self addConstraints:@[leftButtonXConstraint, leftButtonYConstraint, widthConstraint, heightConstraint]];

SWIFT:

btnCoin.translatesAutoresizingMaskIntoConstraints = false// Leading space to superviewlet leftButtonXConstraint = NSLayoutConstraint(    item: btnCoin,    attribute: .left,    relatedBy: .equal,    toItem: self,    attribute: .left,    multiplier: 1.0,    constant: 30)// Top space to superview Ylet leftButtonYConstraint = NSLayoutConstraint(    item: btnCoin,    attribute: .top,    relatedBy: .equal,    toItem: self,    attribute: .top,    multiplier: 1.0,    constant: 258)// Fixed widthlet widthConstraint = NSLayoutConstraint(    item: btnCoin,    attribute: .width,    relatedBy: .equal,    toItem: nil,    attribute: .notAnAttribute,    multiplier: 1.0,    constant: 35)// Fixed Heightlet heightConstraint = NSLayoutConstraint(    item: btnCoin,    attribute: .height,    relatedBy: .equal,    toItem: nil,    attribute: .notAnAttribute,    multiplier: 1.0,    constant: 12)

In the code above i set left button constraints. Here is the output: