Class UISwipeGestureRecognizer

Class UISwipeGestureRecognizer is a subclass of UIGestureRecognizer. It gives you no control over how long or fast or straight the swipe is required to be. But that’s good: if every app used this recognizer, they would all have the same requirements.

I don’t see any claim in the documentation that a single UISwipeGestureRecognizer can recognize both a left swipe or a right swipe, so I made a separate recognizer for each direction. A swipe consists of just one touch, but there may be gestures that consist of a larger numberOfTouches.

Source code in Swipe.zip

1. main.m
2. Class SwipeAppDelegate
3. Class View

Things to try

1. Create the four recognizers with a loop. In the initWithFrame: method of class View, change

   		UISwipeGestureRecognizer *recognizer = [[UISwipeGestureRecognizer alloc]
   			initWithTarget: self action: @selector(swipe:)
   		];
   		recognizer.direction = UISwipeGestureRecognizerDirectionRight;
   		[self addGestureRecognizer: recognizer];
   
   		recognizer = [[UISwipeGestureRecognizer alloc]
   			initWithTarget: self action: @selector(swipe:)
   		];
   		recognizer.direction = UISwipeGestureRecognizerDirectionLeft;
   		[self addGestureRecognizer: recognizer];
   
   		recognizer = [[UISwipeGestureRecognizer alloc]
   			initWithTarget: self action: @selector(swipe:)
   		];
   		recognizer.direction = UISwipeGestureRecognizerDirectionUp;
   		[self addGestureRecognizer: recognizer];
   
   		recognizer = [[UISwipeGestureRecognizer alloc]
   			initWithTarget: self action: @selector(swipe:)
   		];
   		recognizer.direction = UISwipeGestureRecognizerDirectionDown;
   		[self addGestureRecognizer: recognizer];
   

   to

   		static const UISwipeGestureRecognizerDirection a[] = {
   			UISwipeGestureRecognizerDirectionRight,
   			UISwipeGestureRecognizerDirectionLeft,
   			UISwipeGestureRecognizerDirectionUp,
   			UISwipeGestureRecognizerDirectionDown
   		};
   		static const size_t n = sizeof a / sizeof a[0];
   
   		for (size_t i = 0; i < n; ++i) {
   			UISwipeGestureRecognizer *recognizer = [[UISwipeGestureRecognizer alloc]
   				initWithTarget: self action: @selector(swipe:)
   			];
   
   			recognizer.direction = a[i];
   			[self addGestureRecognizer: recognizer];
   		}
   



2. Create the four arrows with a dictionary. Add the following instance variable to class View.

   	NSDictionary *arrows;
   

   Initialize the dictionary in the initWithFrame: method of class View before you create the gesture recognizers. The @() is an Objective-C literal that creates an NSNumber object.

   	arrows = [NSDictionary dictionaryWithObjectsAndKeys:
   		@"→", @(UISwipeGestureRecognizerDirectionRight),
   		@"←", @(UISwipeGestureRecognizerDirectionLeft),
   		@"↑", @(UISwipeGestureRecognizerDirectionUp),
   		@"↓", @(UISwipeGestureRecognizerDirectionDown),
   		nil
   	];
   

   In the swipe: method of class View, change

   	NSString *direction = @"unknown";
   	if (recognizer.direction == UISwipeGestureRecognizerDirectionRight) {
   		direction = @"→";
   	} else if (recognizer.direction == UISwipeGestureRecognizerDirectionLeft) {
   		direction = @"←
   	} else if (recognizer.direction == UISwipeGestureRecognizerDirectionUp) {
   		direction = @"↑";
   	} else if (recognizer.direction == UISwipeGestureRecognizerDirectionDown) {
   		direction = @"↓";
   	}
   

   to

   	NSString *direction = [arrows objectForKey:
   		[NSNumber numberWithInt: recognizer.direction]
   	];
   
   	if (direction == nil) {
   		direction = @"unknown";
   	}