TULayoutAdditions is a collection of helper objects and categories that makes auto layout on iOS dead simple.

Installation

Manually

1. Copy the TULayoutAdditions subfolder into your project.
2. The only required framework is UIKit and iOS 6.0.
3. Import TULayoutAdditions.h.

Example

See the example project.

With traditional auto layout, you would write all this:

greenView.translatesAutoresizingMaskIntoConstraints = NO;

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[greenView]-(10)-[redView]"
                                                                  options:0
                                                                  metrics:nil
                                                                    views:NSDictionaryOfVariableBindings(redView, greenView)]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[blueView]-(>=10)-[greenView(100@250)]"
                                                                  options:0
                                                                  metrics:nil
                                                                    views:NSDictionaryOfVariableBindings(blueView, greenView)]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:greenView attribute:NSLayoutAttributeBottom
                                                      relatedBy:NSLayoutRelationEqual
                                                         toItem:redView
                                                      attribute:NSLayoutAttributeBottom
                                                     multiplier:1.0
                                                       constant:0.0]];

But with TULayoutAdditions, you would do the following:

greenView.constrainedTop = [[blueView.constrainedBottom greaterThanOrEqual] plus:10.0];
greenView.constrainedBottom = redView.constrainedBottom;
greenView.constrainedHeight = [[@100 constraint] withPriority:UILayoutPriorityDefaultLow];
greenView.constrainedRight = [redView.constrainedLeft minus:10.0];
greenView.constrainedLeft = @10;

While the visual formatting language is useful, the large amount of options, need to pass in the views you use, and the fact that it is represented as a string that cannot produce warnings at compile time or auto complete, make it cumbersome and time consuming to write.

TULayoutAdditions is centered around properties starting with constrained, i.e. constrainedHeight, constrainedCetnerX, etc. When you get one of these properties, an instance of TUConstraintInfo is created with the info about the view and the attribute. You can then manipulate properties and even chain them together. Alternatively, you can use and NSNumber to generate a TUConstraintInfo object, which will work as a constant, such as with height and width, or for position attributes (top, left, center, etc.) will implicitly use superview.

Note that the order of operations for plus/minus/times/dividedBy do not apply. If you add first, and then multiply, the constant will not be multiplied. The function will always be mX + b.

Once you have a TUConstraintInfo object, you can then set it on another view's constrained attribute. When you set constraint info on a view, it automatically creates a constraint and adds it to the correct view. It also sets translatesAutoresizingMaskIntoConstraints on both views, unless one is a superview of the other (that is done so that setting a constraint automatically does not invalidate superview constraints).

You can get a reference to the created NSLayoutConstraint in one of two ways.

Blocks

You can create all the constraints inside of a block using +[UIView constraintsWithBlock:] and then get an array of all the constraints created.

NSArray *greenConstraints = [UIView constraintsWithBlock:^{
    greenView.constrainedTop = [[blueView.constrainedBottom greaterThanOrEqual] plus:10.0];
    greenView.constrainedBottom = redView.constrainedBottom;
    greenView.constrainedHeight = [[@100 constraint] withPriority:UILayoutPriorityDefaultLow];
    greenView.constrainedRight = [redView.constrainedLeft minus:10.0];
    greenView.constrainedLeft = @10;
}];

The returned constraints will only include those created with the setConstrainedX: methods, or the -[UIView setConstraintWithAttribute:info: method.

Each setConstrainedX: method is guaranteed to create one and only one constraint each time it is called. That means you can reliably do the following:

NSLayoutConstraint *greenConstraint = [UIView constraintsWithBlock:^{
    greenView.constrainedLeft = @10;
}].lastObject;

Manually create and add constraints

The setConstrainedX: methods just call -[UIView setConstraintWithAttribute:info:] with the corresponding NSLayoutAttribute, which in turn calls -[UIView constraintWithAttribute:info:] and adds it. You can use these methods yourself:

NSLayoutConstraint *constraint = [greenView constraintWithAttribute:NSLayoutAttributeLeft info:@10];
[constraint add];