iOS Auto Layout Demystified

Erica Sadun is the bestselling author, coauthor, and contributor to several dozen books on programming, digital video and photography, and web design, including the widely popular The Core iOS 6 Developer's Cookbook, Fourth Edition. She currently blogs at TUAW.com and has blogged in the past at O'Reilly's Mac Devcenter, Lifehacker, and Ars Technica. In addition to being the author of dozens of iOS-native applications, Erica holds a Ph.D. in computer science from Georgia Tech's Graphics, Visualization, and Usability Center. A geek, a programmer, and an author, she's never met a gadget she didn't love. When not writing, she and her geek husband parent three geeks-in-training, who regard their parents with restrained bemusement when they're not busy rewiring the house or plotting global domination.

Preface   xiii
Chapter 1: Introducing Auto Layout   1
Origins   1
Saying “Yes” to Auto Layout   2
Geometric Relationships   3
Content-Driven Layout   5
Prioritized Rules   6
Inspection and Modularization   6
Incremental Adoption   6
Constraints   7
Satisfiability   7
Sufficiency   8
Constraint Attributes   11
About Those Missing Views   12
Underconstrained Missing Views   13
Missing Views with Inconsistent Rules   14
Tracking Missing Views   14
Ambiguous Layout   15
Exercising Ambiguity   16
Visualizing Constraints   17
Intrinsic Content Size   18
Compression Resistance and Content Hugging   20
Image Embellishments   22
Alignment Rectangles   22
Visualizing Alignment Rectangles   24
Alignment Insets   24
Declaring Alignment Rectangles   26
Implementing Alignment Rectangles   27
Exercises   29
Conclusions   30
Chapter 2: Constraints   31
Constraint Types   31
Priorities   33
Conflicting Priorities   33
Enumerated Priorities   34
Content Size Constraints   36
Intrinsic Content Size   36
Content Hugging   36
Compression Resistance   38
Setting Content Size Constraints in Code   39
Setting Content Size Constraints in IB   40
Building Layout Constraints   41
The Layout Constraint Class   42
Constraint Math   42
First and Second Items   43
Creating Layout Constraints   44
Building NSLayoutConstraint Instances   45
Unary Constraints   45
Zero-Item Constraints Are Illegal   46
View Items   47
Constraints, Hierarchies, and Bounds Systems   48
Installing Constraints   50
Removing Constraints   52
Comparing Constraints   54
Matching Constraints   55
Laws of Layout Constraints   57
Exercises   59
Conclusions   59
Chapter 3: Interface Builder Layout   61
Designing in IB   61
Disabling Auto Layout   62
Opting Out of Auto Layout in Code   63
Combining Autosizing with Auto Layout   64
Basic Layout and Auto-Generated Constraints   64
Inferred Constraints   64
Ambiguity Resolution Constraints   67
Size Constraints   69
A Guided Tour of IB Elements   69
Constraint Listings   76
Xcode Labels   78
Adding Xcode Identities   79
Adding Constraints   80
Dragging   81
Pinning and Aligning   83
Previewing Layouts   85
Inspecting Constraints   88
View Size Inspector   90
Frame and Layout Rectangles   91
Other Size Inspector Items   92
The Resolution Menu   92
Updating Frames and Constraints   92
Adding and Resetting Constraints   93
Clearing Constraints   93
Constraints/Resizing Pop-Up Menu   93
Descendants   94
Siblings and Ancestors   95
The Missing Views Problem   95
Balancing Requests   97
Hybrid Layout   100
Building a Nib File for Testing   100
Adding the Nib File in Code   101
Advantages of Hybrid Layout   102
Removing IB-Generated Constraints   104
Exercises   105
Conclusions   108
Chapter 4: Visual Formats   109
Introducing Visual Format Constraints   109
Options   111
Alignment   112
Skipping Options   113
Variable Bindings   113
The Problem with Indirection   113
Indirection Workaround   114
Metrics   115
Real-World Metrics   115
Format String Structure   116
Orientation   116
Retrieving Constraints by Axis   117
View Names   117
Superviews   118
Connections   118
Empty Connections   118
Standard Spacers   119
Numeric Spacers   120
Referencing the Superview   120
Spacing from the Superview   122
Flexible Spaces   122
Parentheses   123
Negative Numbers   124
Priorities   124
Multiple Views   125
View Sizes   126
Format String Components   128
Getting It Wrong   130
NSLog and Visual Formats   131
Constraining to a Superview   132
View Stretching   133
Constraining Size   134
Building Rows or Columns   135
Matching Sizes   136
Why You Cannot Distribute Views   137
How to Pseudo-Distribute Views (Part 1: Equal Centers)    138
Pseudo-Distributing Views (Part 2: Spacer Views)    140
Exercises   143
Conclusions   143
Chapter 5: Debugging Constraints   145
Xcode Feedback   145
Development Feedback   145
Compiler Feedback   146
Runtime   146
Reading Console Logs   147
Autosizing Issues Example   147
Solution: Switch Off Autosizing Translation   148
Auto Layout Conflicts Example   149
Solution: Adjusting Priorities   150
The Nuclear Approach   150
The Balance Approach   151
Tracing Ambiguity   151
Examining Constraint Logs   152
Alignment Constraint Example   152
Standard Spacers Example   153
Equation-Based Constraint Example   153
Complex Equation Example   154
Multiplier and Constant Example   155
A Note About Layout Math   155
Constraint Equation Strings   156
Adding Names   159
Using Nametags   160
Naming Views   161
Describing Views   161
Unexpected Padding Example   164
The Hugged Image Example   165
View Centering Example   166
Retrieving Referencing Constraints   167
Descent Reports   169
Ambiguity Example   170
Expanding on Console Dumps Example   172
Visualizing Constraints   173
Automating Visualization   174
Launch Arguments   175
Internationalization   177
Doubled Strings (iOS/OS X)    177
Flipped Interfaces (OS X)    178
Flipped Interfaces (iOS)    179
Profiling Cocoa Layout   181
Auto Layout Rules of Debugging   183
Exercises   183
Conclusions   184
Chapter 6: Building with Auto Layout   185
Basic Principles of Auto Layout   185
Layout Libraries   186
Building Libraries   187
Planning Interfaces   190
Building for Modularity   191
Updating Constraints   194
Calling Updates and Animating Changes   195
Animating Constraint Changes on OS X   196
Fading Changes   197
Designing for Edge Conditions   198
Building a View Drawer   200
Building the Drawer Layout   203
Managing Layout for Dragged Views   206
Dragged Views   207
Window Boundaries   208
Exercises   211
Conclusions   211
Chapter 7: Layout Solutions   213
Table Cells   213
Auto Layout and Multiple-Height Table Cells   216
Preserving Image Aspect   217
Accordion Sizing   220
Scroll Views   221
Scroll Views and Pure Auto Layout   222
Hybrid Solution   222
Building a Paged Image Scroll View   223
Centering View Groups   226
Custom Multipliers and Random Positions   228
Building Grids   231
Making Room for the Keyboard   233
Inserting Views at Runtime   236
Adding iOS Frame and Constraint Overlays   237
Motion Effects, Dynamic Text, and Containers   238
Exercises   238
Conclusions   238
Appendix A: Answers to Exercises   241
Chapter 1   241
Chapter 2   242
Chapter 3   243
Chapter 4   245
Chapter 5   247
Chapter 6   248
Chapter 7   249
Index   251