Event Handling Guide for iOS

Event Handling Guide for iOS Contents About Events in iOS 6 At a Glance 6 UIKit Makes It Easy for Your App to Detect Gestures 6 An Event Travels Along a Specific Path Looking for an Object to Handle It 7 A UIEvent Encapsulates a Touch, Shake-Motion, or Remote-Control Event 7 An App Receives Multitouch Events When Users Touch Its Views 7 An App Receives Motion Events When Users Move Their Devices 8 An App Receives Remote Control Events When Users Manipulate Multimedia Controls 8 Prerequisites 8 See Also 9 Gesture Recognizers 10 Use Gesture Recognizers to Simplify Event Handling 10 Built-in Gesture Recognizers Recognize Common Gestures 11 Gesture Recognizers Are Attached to a View 11 Gestures Trigger Action Messages 11 Responding to Events with Gesture Recognizers 12 Using Interface Builder to Add a Gesture Recognizer to Your App 13 Adding a Gesture Recognizer Programmatically 13 Responding to Discrete Gestures 14 Responding to Continuous Gestures 16 Defining How Gesture Recognizers Interact 17 Gesture Recognizers Operate in a Finite State Machine 17 Interacting with Other Gesture Recognizers 19 Interacting with Other User Interface Controls 22 Gesture Recognizers Interpret Raw Touch Events 23 An Event Contains All the Touches for the Current Multitouch Sequence 23 An App Receives Touches in the Touch-Handling Methods 24 Regulating the Delivery of Touches to Views 25 Gesture Recognizers Get the First Opportunity to Recognize a Touch 25 Affecting the Delivery of Touches to Views 26 Creating a Custom Gesture Recognizer 27 Implementing the Touch-Event Handling Methods for a Custom Gesture Recognizer 28 Resetting a Gesture Recognizer’s State 30 2013-01-28 | © 2013 Apple Inc. All Rights Reserved. 2 Contents Event Delivery: The Responder Chain 31 Hit-Testing Returns the View Where a Touch Occurred 31 The Responder Chain Is Made Up of Responder Objects 33 The Responder Chain Follows a Specific Delivery Path 34 Multitouch Events 37 Creating a Subclass of UIResponder 37 Implementing the Touch-Event Handling Methods in Your Subclass 38 Tracking the Phase and Location of a Touch Event 39 Retrieving and Querying Touch Objects 39 Handling Tap Gestures 42 Handling Swipe and Drag Gestures 42 Handling a Complex Multitouch Sequence 45 Specifying Custom Touch Event Behavior 49 Intercepting Touches by Overriding Hit-Testing 51 Forwarding Touch Events 51 Best Practices for Handling Multitouch Events 53 Motion Events 55 Getting the Current Device Orientation with UIDevice 55 Detecting Shake-Motion Events with UIEvent 57 Designating a First Responder for Motion Events 57 Implementing the Motion-Handling Methods 57 Setting and Checking Required Hardware Capabilities for Motion Events 58 Capturing Device Movement with Core Motion 59 Choosing a Motion Event Update Interval 60 Handling Accelerometer Events Using Core Motion 61 Handling Rotation Rate Data 63 Handling Processed Device Motion Data 65 Remote Control Events 69 Preparing Your App for Remote Control Events 69 Handling Remote Control Events 70 Testing Remote Control Events on a Device 71 Document Revision History 73 2013-01-28 | © 2013 Apple Inc. All Rights Reserved. 3 Figures, Tables, and Listings Gesture Recognizers 10 Figure 1-1 Figure 1-2 Figure 1-3 Figure 1-4 Figure 1-5 Figure 1-6 Table 1-1 Listing 1-1 Listing 1-2 Listing 1-3 Listing 1-4 Listing 1-5 Listing 1-6 Listing 1-7 Listing 1-8 Listing 1-9 A gesture recognizer attached to a view 10 Discrete and continuous gestures 12 State machines for gesture recognizers 18 A multitouch sequence and touch phases 24 Default delivery path for touch events 25 Sequence of messages for touches 26 Gesture recognizer classes of the UIKit framework 11 Adding a gesture recognizer to your app with Interface Builder 13 Creating a single tap gesture recognizer programmatically 13 Handling a double tap gesture 14 Responding to a left or right swipe gesture 15 Responding to a rotation gesture 16 Pan gesture recognizer requires a swipe gesture recognizer to fail 20 Preventing a gesture recognizer from receiving a touch 21 Implementation of a checkmark gesture recognizer 28 Resetting a gesture recognizer 30 Event Delivery: The Responder Chain 31 Figure 2-1 Figure 2-2 Hit-testing returns the subview that was touched 32 The responder chain on iOS 35 Multitouch Events 37 Figure 3-1 Figure 3-2 Figure 3-3 Figure 3-4 Figure 3-5 Listing 3-1 Listing 3-2 Listing 3-3 Listing 3-4 Listing 3-5 Listing 3-6 Relationship of a UIEvent object and its UITouch objects 39 All touches for a given touch event 40 All touches belonging to a specific window 41 All touches belonging to a specific view 41 Restricting event delivery with an exclusive-touch view 50 Detecting a double tap gesture 42 Tracking a swipe gesture in a view 43 Dragging a view using a single touch 44 Storing the beginning locations of multiple touches 46 Retrieving the initial locations of touch objects 46 Handling a complex multitouch sequence 47 2013-01-28 | © 2013 Apple Inc. All Rights Reserved. 4 Figures, Tables, and Listings Listing 3-7 Listing 3-8 Determining when the last touch in a multitouch sequence has ended 49 Forwarding touch events to helper responder objects 52 Motion Events 55 Figure 4-1 Figure 4-2 Table 4-1 Listing 4-1 Listing 4-2 Listing 4-3 Listing 4-4 Listing 4-5 Listing 4-6 Listing 4-7 The accelerometer measures velocity along the x, y, and z axes 61 The gyroscope measures rotation around the x, y, and z axes 63 Common update intervals for acceleration events 60 Responding to changes in device orientation 56 Becoming first responder 57 Handling a motion event 58 Accessing accelerometer data in MotionGraphs 62 Accessing gyroscope data in MotionGraphs 64 Starting and stopping device motion updates 67 Getting the change in attitude prior to rendering 68 Remote Control Events 69 Listing 5-1 Listing 5-2 Listing 5-3 Preparing to receive remote control events 69 Ending the receipt of remote control events 70 Handling remote control events 71 2013-01-28 | © 2013 Apple Inc. 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