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The Core iOS Developer’s Cookbook, Fifth Edition by Rich Wardwell, Erica Sadun

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Recipe: Using Multiple Gesture Recognizers Simultaneously

Recipe 1-3 builds on the ideas presented in Recipe 1-2, but with several differences. First, it introduces multiple recognizers that work in parallel. To achieve this, the code uses three separate recognizers—rotation, pinch, and pan—and adds them all to the DragView’s gestureRecognizers property. It assigns the DragView as the delegate for each recognizer. This allows the DragView to implement the gestureRecognizer:shouldRecognize-SimultaneouslyWithGestureRecognizer: delegate method, enabling these recognizers to work simultaneously. Until this method is added to return YES as its value, only one recognizer will take charge at a time. Using parallel recognizers allows you to, for example, ...

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