www.it-ebooks.info iOS Auto Layout Demystified www.it-ebooks.info Addison-Wesley Mobile Programming Series Visit informit.com/mobile for a complete list of available publications T he Addison-Wesley Mobile Programming Series is a collection of digital-only programming guides that explore key mobile programming features and topics in-depth The sample code in each title is downloadable and can be used in your own projects Each topic is covered in as much detail as possible with plenty of visual examples, tips, and step-by-step instructions When you complete one of these titles, you’ll have all the information and code you will need to build that feature into your own mobile application Make sure to connect with us! informit.com/socialconnect www.it-ebooks.info iOS Auto Layout Demystified Second Edition Erica Sadun Upper Saddle River, NJ • Boston • Indianapolis • San Francisco New York • Toronto • Montreal • London • Munich • Paris • Madrid Cape Town • Sydney • Tokyo • Singapore • Mexico 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work, please submit a written request to Pearson Education, Inc., Permissions Department, One Lake Street, Upper Saddle River, New Jersey 07458, or you may fax your request to (201) 2363290 AirPlay, AirPort, AirPrint, AirTunes, App Store, Apple, the Apple logo, Apple TV, Aqua, Bonjour, the Bonjour logo, Cocoa, Cocoa Touch, Cover Flow, Dashcode, Finder, FireWire, iMac, Instruments, Interface Builder, iOS, iPad, iPhone, iPod, iPod touch, iTunes, the iTunes logo, Leopard, Mac, Mac logo, Macintosh, Multi-Touch, Objective-C, Quartz, QuickTime, QuickTime logo, Safari, Snow Leopard, Spotlight, and Xcode are trademarks of Apple, Inc., registered in the United States and other countries OpenGL and the logo are registered trademarks of Silicon Graphics, Inc The YouTube logo is a trademark of Google, Inc Intel, Intel Core, and Xeon are trademarks of Intel Corp in the United States and other countries ISBN-13: 978-0-321-96719-0 ISBN-10: 0-321-96719-4 Text printed in the United States on recycled paper at RR Donnelley in Crawfordsville, Indiana First printing: October 2013 www.it-ebooks.info Compositor Nonie Ratcliff ❖ Hop Hop THOOM ❖ www.it-ebooks.info Table of Contents Preface xiii Introducing Auto Layout Origins Saying “Yes” to Auto Layout Geometric Relationships Content-Driven Layout Prioritized Rules Inspection and Modularization Incremental Adoption Constraints Satisfiability Sufficiency 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 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 www.it-ebooks.info 20 Contents 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 Comparing Constraints 52 54 Matching Constraints 55 Laws of Layout Constraints 57 Exercises 59 Conclusions 59 Interface Builder Layout Designing in IB 61 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 www.it-ebooks.info vii viii Contents A Guided Tour of IB Elements Constraint Listings 69 76 Xcode Labels 78 Adding Xcode Identities 79 Adding Constraints 80 Dragging 81 Pinning and Aligning Previewing Layouts 83 85 Inspecting Constraints View Size Inspector 88 90 Frame and Layout Rectangles 91 Other Size Inspector Items The Resolution Menu 92 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 Hybrid Layout 97 100 Building a Nib File for Testing Adding the Nib File in Code Advantages of Hybrid Layout 100 101 102 Removing IB-Generated Constraints 104 Exercises 105 Conclusions 108 Visual Formats 109 Introducing Visual Format Constraints 109 Options 111 Alignment 112 Skipping Options Variable Bindings 113 113 The Problem with Indirection 113 Indirection Workaround 114 www.it-ebooks.info Contents 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 Numeric Spacers 119 120 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 www.it-ebooks.info ix Chapter When can you skip implementing updateViewConstraints and updateConstraints? If there are no circumstances where your layout will change and invalidate the current constraint set, you not need to implement these update methods You see this with simple layouts that easily adapt to portrait and landscape presentation For example, a view with three centered buttons (for example, Load Game, New Game, and Credits) does not require orientation-specific design tweaks Chapter How can you duplicate Listing 7-7’s spacer solution in IB? Add two spacer views and, for convenience, give them a background color Constrain them to the left and right (or top and bottom) and match their widths (or heights) to each other Pin the horizontal (vertical) spaces between the first spacer and the first view and between the last view and the last spacer Edit the constants to zero Finish by reverting the two views’ background colors to clear How you set view aspect in IB? You cannot perform any multiplier-dependent tasks, including setting aspect, in IB Use code instead Can you use the keyboard spacer from Listing 7-10 in IB? Yes, but you have to modify the code a little bit Follow these steps: a In Listing 7-10, the height constraint is an instance variable Adjust this to a class property so you can assign a constraint from IB and update code references from heightConstraint to _heightConstraint b Add a plain view to the IB editor Set its class to KeyboardSpacingView by using the Identity Inspector c Pin it to the bottom of the superview and stretch it horizontally Add a text view above it and pin the vertical space between the two, adjusting the constant to Add a new height constraint to the view and set its constant to Assign the constraint to the class property d Make sure you call establishNotificationHandlers in viewDidLoad so the view responds to keyboard events How you use the hybrid scroller strategy from Listing 7-5 in IB? The easiest way is to create a separate xib file and lay out the scroll view contents there Create the scroll view in your normal storyboard and set its class to AutoLayoutScrollView At runtime, load the content view from the xib file and add it to the scroll view’s customContentView www.it-ebooks.info 249 This page intentionally left blank www.it-ebooks.info Index A accordion-style constraints, 220-221 addImageView: method, 218 addView: method, 203 alignment constraint debugging, 152-153 frames, 26-28 geometry in Cocoa/Cocoa Touch, 26 image embellishments insets, 24-26 rectangles, 22-24, 26-29 imageWithAlignmentRectInsets: method, 24 layout constraints, 71, 81, 83-85 NSViewShowAlignmentRects class, 24, 176 UIViewShowAlignmentRects class, 24, 27, 176 visual format constraints flush, 129 masks, 111 perpendicular to format, 112 skipping options, 113 vertical or horizontal, 116-117, 130 alignmentRectForFrame: method, 26-27 www.it-ebooks.info 252 alignmentRectInsets method alignmentRectInsets method, 26-27 grids, 231-233 ambiguity hybrid layouts, 100-104 exerciseAmbiguityInLayout view method, 16 iOS containers, 238 hasAmbiguousLayout property, 15 dynamic text, 238 layout constraints, 15-16 motion effects, 238 resolution of, 67-68, 71 keyboards, 233-236 tracing ambiguity, 151-152 layout libraries problems, 151-152, 170-172 tracing, 170-172 advantages, 189-190 of functions, 188-189 ancestorSharedWithView: method, 48 guidelines for building, 190 AppleTextDirection class, 176, 178 of macro definitions, 187-188 Application Button, 21 of methods, 189 Assistant Editor, 75 solving redundancy and density, 186-187 Attributes Inspector Is Initial View Controller, 70 modular designs, 191-194 Placeholder, 104 opting out of in code, 64-65 Simulated Metrics origins, 1-2 Orientation, 70 reasons for using, 2-3 Orientation/Landscape or Portrait, 97 using, 88-90 backward compatibility, content-driven layout, geometric relationships, 3-5 Auto Layout incremental adoption, accordion-style constraints, 220-221 inspection and modularization, and Autosizing, combining with, 64 prioritized rules, building interfaces scroll views advantages, 62 hybrid layout, 222-223 basic principles, 185-186 overview, 221 dragging views, 206-208 with paged image, 223-226 planning and rules, 190-191 pure Auto Layout, 222 disabling, 62-63 table cells edge conditions design constraint-based, 213 control for locking/unlocking, 198-200 view drawer, 200-206 www.it-ebooks.info guidelines for using, 213-216 multiple-height, 216-217 constraint debugging views C centering groups, 226-228 Cassowary dragging, 206-208 image aspect preservation, 217-219 rule-based system, inserting at runtime, 236-238 SourceForge project page, positioning randomly with constraints, 228-230 Cocoa/Cocoa Touch alignment geometry, 26 positioning with custom multipliers, 228 constraints window boundaries satisfiability, 7-8 constraints limiting size, 209 sufficiency, 8-11 constraints preventing view clipping, 209 Layout profiling tool, 181-183 console logs, 147 draggable views overruling sizing, 209-210 view placement within, 208-209 AutoLayoutScrollView class, 222-223 autoresizingMask property, 63 Autosizing, basis for Auto Layout, alignment, 152-153 autosizing issues/solutions, 147-149 equation-based constraints, 153-154 multiplier and constants in constraints, 155 rule conflicts/solutions, 149-151 and Auto Layout combining with, 64 constraint-based feature, 61 opting to participate in, 64-65 debugging constraints, 147-149 hybrid layouts, 100-104 struts and springs, 61 standard spacers, 153 tracing ambiguity, 151-152 constraint debugging ambiguity problems, 170-172 tracing ambiguity, 151-152 Cocoa Layout profiling tool, 181-183 console logs, 147 alignment, 152-153 B Badros, Greg J., baselineOffsetFromBottom method, 26-27 autosizing issues/solutions, 147-149 equation-based constraints, 153-154 Borning, Alan, multiplier and constants in constraints, 155 bounds systems, 48 rule conflicts/solutions, 149-151 standard spacers, 153 tracing ambiguity, 151-152 www.it-ebooks.info 253 254 constraint debugging content layout math, 155-156 D descent reports, 169-170 debugging constraints equation strings, 156-159 ambiguity problems, 170-172 internationalization, 177 doubled strings, 177-178 flipped interfaces, 178-181 tracing ambiguity, 151-152 Cocoa Layout profiling tool, 181-183 console logs, 147 nametags alignment, 152-153 for objects, 159-161 autosizing issues/solutions, 147-149 for views, 161 rules, 183 equation-based constraints, 153-154 views, 172-173 describing, 161-164 hugged images, 165-166 multiplier and constants in constraints, 155 padding, 164-165 rule conflicts/solutions, 149-151 referencing, 167-169 standard spacers, 153 visualizing constraints, 173-174 Xcode feedback, 145 tracing ambiguity, 151-152 content layout math, 155-156 compiler, 146 descent reports, 169-170 development, 145-146 equation strings, 156-159 launch arguments, 175-177 internationalization, 177 runtime, 147 doubled strings, 177-178 constraints See layout constraints; visual format constraints constraintsAffectingLayoutForAxis: view method, 117 constraintsAffectingLayoutForOrientation: view method, 117 Content Compression Resistance Priority setting, 20-21, 74, 96, 99 flipped interfaces, 178-181 nametags for objects, 159-161 for views, 161 rules, 183 views, 172-173 describing, 161-164 Content Hugging Priority setting, 21, 74 hugged images, 165-166 contentSize property, 221-223, 225 padding, 164-165 contentView property, 223, 226 referencing, 167-169 visualizing constraints, 173-174 www.it-ebooks.info IB (Interface Builder) Xcode feedback, 145 firstItem/secondItem properties, 42 compiler, 146 frames launch arguments, 175-177 frameForAlignmentRect: method, 26-28 runtime, 147 resolving issues, 92 development, 145-146 updating, 92, 96 descent reports, 169-170 G-H E grids, 231-233 edge conditions design Hepting, Steven, 233 control for locking/unlocking, 198-200 hierarchies of views, 24-26 descent reports, 169-170 view drawer, 200-206 hybrid layouts, 32 Editor Align, 80, 83-85 advantages, 102 Canvas Auto Layout, 100-104 scroll views, 222-223 Show Bound Rectangles, 91 Show Involved Views for Selected Constraint, 82 nib files for testing, 100 nib files in code, 101 Show Layout Rectangles, 91 Pin, 80, 83-85 I-J Horizontal Spacing, 96, 98 Resolve Auto Layout Issues Add Missing Constraints, 72, 93 Clear Constraints, 93 Reset to Suggested Constraints, 72-73, 93 Update Constraints, 72, 92 Exercise Ambiguity button, 17 F IB (Interface Builder) Assistant Editor, 75 Attributes Inspector Is Initial View Controller, 70 Placeholder, 104 Simulated Metrics/Orientation, 70 Simulated Metrics/Orientation/ Landscape or Portrait, 97 Autosizing combining with Auto Layout, 64 File Inspector, disabling Use Autolayout box, 62 versus constraint-based Auto Layout, 61 firstAttribute/secondAttribute properties, 42 opting out in code, 63-64 www.it-ebooks.info 255 256 IB (Interface Builder) browse constraints, Size Inspector, 21 components, 70-76 Content Compression Resistance Priority setting, 20-21, 74, 96, 99 Constraints listings, 76-78 Content Hugging Priority setting, 21, 74 Editor Align, 80, 83-85 list of constraints per view, 74, 82-83 Canvas/Show Bound Rectangles, 91 Canvas/Show Involved Views for Selected Constraint, 82 options when Auto Layout is enabled, 63 Canvas/Show Layout Rectangles, 91 view sizes, 90 Top and Bottom Layout Guide proxies, 70 Pin, 80, 83-85 Pin/Horizontal Spacing, 96, 98 Identity Inspector, 97 Resolve Auto Layout Issues/Add Missing Constraints, 72, 93 Resolve Auto Layout Issues/Clear Constraints, 93 User Defined Runtime Attributes, 161 image embellishments alignment insets, 24-26 Resolve Auto Layout Issues/Reset to Suggested Constraints, 72-73, 93 alignment rectangles, 22-23 Resolve Auto Layout Issues/Update Constraints, 73, 92 implementing, 27-29 declaring, 26-27 visualizing, 24 File Inspector, disabling Use Autolayout box, 62 imageWithAlignmentRectInsets: method, 24 Identity Inspector, 97 install method, 135 User Defined Runtime Attributes, 161 installToView: method, 233-236 Interface Builder See IB Issue Navigator, 146 internationalization, 177 Issue Stepper, 71, 145 doubled strings, 177-178 layouts, validating and checking, modular interface design, 191-193 overview, 61-62 Preview, 86-88 preview panes, 72 flipped interfaces, 178-181 intrinsicContentSize method, 18 isEqualToLayoutConstraint: method, 54 Issue Navigator, 146 Issue Stepper, 71, 145 Root View Controller, 97 satisfiability, www.it-ebooks.info layout constraints content size, 31, 36 K-L compression resistance, 38 keyboards, 233-236 content compression, 92, 96, 99 layout constraints, 31, 33 See also views; visual format constraints accordion-style, 220-221 with Add Missing Constraints, 93 list of requests, 81 by pinning and aligning, 83-85 adding/removing at runtime, 13 alignment, 70, 81, 83-85 alignment insets, 24-26 alignment rectangles, 22-23 declaring, 26-27 implementing, 27-29 inspecting, 91 visualizing, 24 ambiguous, 15-16 resolution of, 67-68, 70 tracing ambiguity, 151-152 attributes, 41 invalid pairings, 58-59 autosizing, 31 balancing touches, 200 baseline, 11, 81 basics, bounding rectangles, 91 bounds systems, 48, 58 browsing, Cassowary, centerX and centerY, 11 clearing, 93 comparing, 54 in IB, 39 intrinsic, 36, 74 adding by dragging, 81-83 content hugging, 36-37, 92 in UIKit and AppKit, 39-40 cycles, 57 editing, 74 exercising, 16-17 first and second items, 43-44 horizontal or vertical center in container, 81, 88 centers, 81 spacing, 81, 96 inferred, 65-67, 104 inspecting constraints, 88-90 view sizes, 90-92 installing, 50-51 self-installing, 51-52 iOS view dynamics, 57 laws, 57-59 layout support, 31 leading and trailing, 11 left and right, 11 edges, 81 libraries of common requests, matching, 55-56, 70, 236-237 math, 41-43 methods of creating, 44 motion effects, 58 pinning, 70, 83-85 placeholders, 104-105 www.it-ebooks.info 257 258 layout constraints priorities, 33, 57 layout relations adjustments, 35, 150-151 NSLayoutRelationEqual, 12 conflicting priorities, 33-34 NSLayoutRelationGreaterThanOrEqual, 12 enumerated priorities, 34-35 NSLayoutRelationLessThanOrEqual, 12 prototyping, 31 rank of requests, 33 libraries redundancy, 57 constraint requests, relations, 41, 57 layouts debugging, 157-159 advantages, 189-190 removing, 52-54 of functions, 188-189 resetting, with Reset to Suggested Constraints, 93 guidelines for building, 190 rules conflicts, 149, 183 of macro definitions, 187-188 runtime failures, 58 of methods, 189 sizing/resizing, 69-70, 93-94 solving redundancy and density, 186-187 descendants, 94 siblings and ancestors, 95 loadView method, 6, 16, 222 spacing, 70 M top and bottom, 11 edges, 81 missing views, 95-97 transforms, 57 with inconsistent rules, 14 unary, 20-22 tracking, 14-15 updating, 92 underconstrained, 13 animating updates, 196 modular interface design, 191-194 fading changes, 197 updateConstraints method, 194-195 moveToPosition: method, 207 multiplier/constant properties, 42 updateViewConstraints method, 194-197 N-O visualizing, 17, 173-174 width or height, 11, 81 nametags equally, 81 for objects, 159-161 negative values unusable, 12 for views, 161 Xcode identities, 79-80 Xcode labels, 78-79 NSAutoresizingMaskLayoutConstraint class, 31 hybrid systems, 32 zero-item, 21-22 www.it-ebooks.info setNeedsUpdateConstraints method NSConstraintBasedLayoutEngageNonLazily class, 176 NSLayoutPriority class, 21 NSConstraintBasedLayoutLogUnsatisfiable class, 177 NSLog class, 131-132 NSLocalizedString() method, 177 NSConstraintBasedLayoutPlaySoundOnUnsatisfiable class, 176 NSConstraintBasedLayoutPlaySoundWhenEngaged class, 176 NSConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints class, 176 NSContentSizeLayoutConstraint class, 31 NSShowAllViews class, 176 NSUserInterfaceItemIdentification protocol, 159 NSView class, 15-16 NSViewShowAlignmentRects class, 24, 176 NSWindow class, 17 images and controls, 32 NSDictionaryOfVariableBindings() macro, 113 P-Q NSDoubleLocalizedStrings class, 176 Preview, 86-88 NSForceRightToLeftWritingDirections class, 176, 178 preview panes, 76 NSIBPrototypingLayoutConstraint class, 31 private classes, 31-32 priority property, 42 NSLayoutConstraint class, 7, 31 R collections of arrays, 50 commonly used, 32 refersToView: method, 167 creating, 44-45 relation property, 42 instances, 45 removeConstraint: and removeConstraints: methods, 52-54 properties comparing, 54 removeView: method, 203 firstAttribute/secondAttribute, 42, 47, 54 Root View Controller, 97 firstItem/secondItem, 42, 48, 54 S matching, 55-56 multiplier/constant, 42, 54 priority, 42, 54 relation, 42, 54 returning view-specific properties, 47-48 unary constraints, 45-46 zero-item constraints, 46 scroll views hybrid layout, 222-223 overview, 221 with paged image, 223-226 pure Auto Layout, 222 setNeedsUpdateConstraints method, 195, 202-203, 214 www.it-ebooks.info 259 260 Size Inspector switchLabelText: method, 98-99 Size Inspector, 21 Content Compression Resistance Priority setting, 20-21, 70, 96, 99 systemLayoutSizeFittingSize: method, 216 Content Hugging Priority setting, 21, 70 T list of constraints per view, 70, 82-83 options when Auto Layout is enabled, 63 table cells constraint-based, 213 guidelines for using, 213-216 view sizes, 90 multiple-height, 216-217 spacers/spacing, 70 fixed spacers, 129 toggleVisualLayoutHints method, 238 flexible spacers, 122-123, 129 Top and Bottom Layout Guide proxies, 70 horizontal or vertical, 81, 96, 98 typedef float UILayoutPriority, 21 numeric spacers, 120-121 pseudo-distributing, spacer views, 140-143 standard spacers, 119, 153 superviews, spacing from, 122 leading and trailing, 81 top and bottom, 81 U UIConstraintBasedLayoutEngageNonLazily class, 176 UIConstraintBasedLayoutLogUnsatisfiable class, 177 UIConstraintBasedLayoutPlaySoundOnUnsatisfiable class, 176 springs in Autosizing, 61 stringValue method, 156 UIConstraintBasedLayoutPlaySoundWhenEngaged class, 176 struts in Autosizing, 61 superviews, 118, 129 bindings dictionary, 118 UIConstraintBasedLayoutVisualizeMutuallyExclusiveConstraints class, 177 centering views to, 166-167 UIEdgeInset class, 26 constraining views to, 132-133 UIGestureRecognizerStateBegan class, 207 inset from, 130 UIGestureRecognizerStateEnded class, 207 custom, 130 referencing, 120, 167-169 referencingConstraintsInSuperviews: method, 167 spacing from, 122 leading and trailing, 81 UIImageView class, 165 UIKit, enumerated priorities, 34-35 UILayoutGuide objects, properties, bottom LayoutGuide, 32 UILayoutSupport protocol, 130 top and bottom, 81 stretching views to, 133-134 updating constraints, 194 www.it-ebooks.info views UILayoutSupportConstraint class, 31-32 properties baseline, 41 bounds systems, 48 bottomLayoutGuide, 32 centering, groups, 226-228 topLayoutGuide, 32-33 centerX/centerY, 41 content UIScrollView class, 221-223 UITableViewCell subclass, 214 compression resistance, 20-21 UIView class, 15-16 content hugging, 21 UIViewContentModeScaleAspectFit class, 219 intrinsic size, 18-19 debugging, 172-173 UIViewContentModeScaleToFill class, 217, 219 describing, 161-164 dragging, 206-208 UIViewController class, 97 draggable views overruling sizing, 209-210 UIViewShowAlignmentRects class, 24, 27, 176 hugged images, 165-166 unsigned integers, constraint priorities, 33 updateConstraints method, 194-195, 202-206, 224-226 image aspect preservation, 217-219 inserting at runtime, 236-238 leading/trailing edges, 41 updateViewConstraints method, 6, 194-197 left, right, top, or bottom, 41 missing, 95-97 with inconsistent rules, 14 V tracking, 14-15 VIEW_CLASS constant, 15, 47-48 multiple view widths, 220-221 ViewController class, 97 multipliers, 41 viewDidAppear: method, 66, 68-69, 132, 238 padding, 164-165 viewDidLoad method, 222 placeholders, 41 views See also layout constraints; visual format constraints positioning adding/relinquishing management of, 202-203 custom, 228 with custom multipliers, 228 randomly with constraints, 228-230 additive constants, 41 referencing, 167-169 alignment insets, 24-26 relations of equalities/inequalities, 41 alignment rectangles, 22-23 stretching to superviews, 133-134 declaring, 26-27 width/height, 41 implementing, 27-29 visualizing, 24 www.it-ebooks.info 261 262 visual format constraints views, 130 visual format constraints alignment masks, 111 building rows or columns, 135-136 flush, 129 distributing, 137 perpendicular to format, 112 pseudo-distributing, equal centers, 138-139 skipping options, 113 pseudo-distributing, spacer views, 140-143 vertical or horizontal, 116-117, 130 Apple preferences, 111 width/height bindings dictionary, 113-115 fixed, 129 views, 130 match with another view, 129 connections minimum and maximum, 129 empty, 118 visualizeConstraints method, 17 fixed spacers, 129 flexible spacers, 122-123, 129 negative numbers, 124 W-X-Y-Z numeric spacers, 120-121 window boundaries parentheses, 123-124 constraints limiting size, 209 priorities, 124-125, 130 constraints preventing view clipping, 209 standard spacers, 119, 153 direction masks, 111 draggable views overruling sizing, 209-210 examples, 110-111 format string components, 128-130 common errors, 129-131 view placement within, 208-209 Xcode format string structure, 116 advantages, 62 versus manually built constraints, 111 constraints metrics, 129 conflicting, 7, 96 metrics dictionary, 115 identities, 79-80 real-world metrics, 115-116 labels, 78-79 NSLayoutConstraint class, 109 disadvantages, 44 orientation, 116-117 feedback, 145 relations, 129 compiler, 146 variable bindings, 113 development, 145-146 indirection problems, 113-114 launch arguments, 175-177 indirection workarounds, 114-115 runtime, 147 view names, 117-118, 161 new top and bottom layout guides, 67 view sizes, 126-127 constraining, 134-135 matching, 136-137 www.it-ebooks.info This page 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Layout Constraints 57 Exercises 59 Conclusions 59 Interface Builder Layout Designing in IB 61 61 Disabling Auto Layout 62 Opting Out of Auto Layout in Code 63 Combining Autosizing with Auto Layout. .. (iOS) 179 Profiling Cocoa Layout 181 Auto Layout Rules of Debugging 183 Exercises 183 Conclusions 184 Building with Auto Layout 185 Basic Principles of Auto Layout 185 Layout Libraries 186 Building... ■ Auto Layout is declarative You express the interface behavior without worrying about how those rules get implemented Just describe the layout; let Auto Layout calculate the frames ■ Auto Layout