Class

UILayoutGuide

A rectangular area that can interact with Auto Layout.

Declaration

@interface UILayoutGuide : NSObject

Overview

Use layout guides to replace the dummy views you may have created to represent inter-view spaces or encapsulation in your user interface. Traditionally, there were a number of Auto Layout techniques that required dummy views. A dummy view is an empty view that does not have any visual elements of its own and serves only to define a rectangular region in the view hierarchy. For example, if you wanted to use constraints to define the size or location of an empty space between views, you needed to use a dummy view to represent that space. If you wanted to center a group of objects, you needed a dummy view to contain those objects. Similarly, dummy views could be used to contain and encapsulate part of your user interface. Dummy views let you break up a large, complex user interface into self-contained, modular chunks. When used properly, they could greatly simplify your Auto Layout constraint logic.

There are a number of costs associated with adding dummy views to your view hierarchy. First, there is the cost of creating and maintaining the view itself. Second, the dummy view is a full member of the view hierarchy, which means that it adds overhead to every task the hierarchy performs. Worst of all, the invisible dummy view can intercept messages that are intended for other views, causing problems that are very difficult to find.

The UILayoutGuide class is designed to perform all the tasks previously performed by dummy views, but to do it in a safer, more efficient manner. Layout guides do not define a new view. They do not participate in the view hierarchy. Instead, they simply define a rectangular region in their owning view’s coordinate system that can interact with Auto Layout.

Creating Layout Guides

To create a layout guide, you must perform the following steps:

  1. Instantiate a new layout guide.

  2. Add the layout guide to a view by calling the view’s addLayoutGuide: method.

  3. Define the position and size of the layout guide using Auto Layout.

You can use these guides to define the space between elements in your layout. The following example shows layout guides used to define an equal spacing between a series of views.

UILayoutGuide *space1 = [[UILayoutGuide alloc] init];
[self.view addLayoutGuide:space1];
 
UILayoutGuide *space2 = [[UILayoutGuide alloc] init];
[self.view addLayoutGuide:space2];
 
[space1.widthAnchor constraintEqualToAnchor:space2.widthAnchor].active = YES;
[self.saveButton.trailingAnchor constraintEqualToAnchor:space1.leadingAnchor].active = YES;
[self.cancelButton.leadingAnchor constraintEqualToAnchor:space1.trailingAnchor].active = YES;
[self.cancelButton.trailingAnchor constraintEqualToAnchor:space2.leadingAnchor].active = YES;
[self.clearButton.leadingAnchor constraintEqualToAnchor:space2.trailingAnchor].active = YES;

Layout guides can also act as a black box, containing a number of other views and controls. This lets you encapsulate part of your view, breaking your layout into modular chunks.

UILayoutGuide *container = [[UILayoutGuide alloc] init];
[self.view addLayoutGuide:container];
 
// Layout the contents of the container
[self.label.lastBaselineAnchor constraintEqualToAnchor:self.textField.lastBaselineAnchor].active = YES;
[self.label.leadingAnchor constraintEqualToAnchor:container.leadingAnchor].active = YES;
[self.textField.leadingAnchor constraintEqualToAnchor:self.label.trailingAnchor constant:8.0].active = YES;
[self.textField.trailingAnchor constraintEqualToAnchor:container.trailingAnchor].active = YES;
[self.textField.topAnchor constraintEqualToAnchor:container.topAnchor].active = YES;
[self.textField.bottomAnchor constraintEqualToAnchor:container.bottomAnchor].active = YES;
 
// Set exterior constraints.
UILayoutGuide *margins = self.view.layoutMarginsGuide;
 
[container.leadingAnchor constraintEqualToAnchor:margins.leadingAnchor].active = YES;
[container.trailingAnchor constraintEqualToAnchor:margins.trailingAnchor].active = YES;
[container.topAnchor constraintEqualToAnchor:self.topLayoutGuide.bottomAnchor constant:20.0].active = YES;

Topics

Working With Layout Guides

identifier

A string used to identify the layout guide.

layoutFrame

The layout guide’s frame in its owning view’s coordinate system.

owningView

The view that owns this layout guide.

Creating Constraints Using Layout Anchors

bottomAnchor

A layout anchor representing the bottom edge of the layout guide’s frame.

centerXAnchor

A layout anchor representing the horizontal center of the layout guide’s frame.

centerYAnchor

A layout anchor representing the vertical center of the layout guide’s frame.

heightAnchor

A layout anchor representing the height of the layout guide’s frame.

leadingAnchor

A layout anchor representing the leading edge of the layout guide’s frame.

leftAnchor

A layout anchor representing the left edge of the layout guide’s frame.

rightAnchor

A layout anchor representing the right edge of the layout guide’s frame.

topAnchor

A layout anchor representing the top edge of the layout guide’s frame.

trailingAnchor

A layout anchor representing the trailing edge of the layout guide’s frame.

widthAnchor

A layout anchor representing the width of the layout guide’s frame.

Debugging the Layout Guide

- constraintsAffectingLayoutForAxis:

The constraints that impact the layout of the guide.

hasAmbiguousLayout

A Boolean value indicating whether the constraints impacting the layout guide specify its location ambiguously.

Relationships

Inherits From

Conforms To

See Also

Layout Guides

NSLayoutDimension

A factory class for creating size-based layout constraint objects using a fluent API.