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. Class AppDelegate.swift: unchanged.
2. Class ViewController.swift: unchanged.
3. Class View.swift: subclass of UITextView. Added methods init and swipe(_:).
4. Main.storyboard
5. Info.plist

Things to try

1. Create the four recognizers with an array and a for-in loop. In the init method of class View, change

   		let rightRecognizer: UISwipeGestureRecognizer =
   			UISwipeGestureRecognizer(target: self, action: #selector(View.swipe(_:)));
   		rightRecognizer.direction = UISwipeGestureRecognizerDirection.Right;
   		addGestureRecognizer(rightRecognizer);
   
   		let leftRecognizer: UISwipeGestureRecognizer =
   			UISwipeGestureRecognizer(target: self, action: #selector(View.swipe(_:)));
   		leftRecognizer.direction = UISwipeGestureRecognizerDirection.Left;
   		addGestureRecognizer(leftRecognizer);
   
   		let upRecognizer: UISwipeGestureRecognizer =
   			UISwipeGestureRecognizer(target: self, action: #selector(View.swipe(_:)));
   		upRecognizer.direction = UISwipeGestureRecognizerDirection.Up;
   		addGestureRecognizer(upRecognizer);
   
   		let downRecognizer: UISwipeGestureRecognizer =
   			UISwipeGestureRecognizer(target: self, action: #selector(View.swipe(_:)));
   		downRecognizer.direction = UISwipeGestureRecognizerDirection.Down;
   		addGestureRecognizer(downRecognizer);
   

   to

   		let directions: [UISwipeGestureRecognizerDirection] = [		//an array
   			UISwipeGestureRecognizerDirection.Right,
   			UISwipeGestureRecognizerDirection.Left,
   			UISwipeGestureRecognizerDirection.Up,
   			UISwipeGestureRecognizerDirection.Down
   		];
   
   		for direction in directions {
   			let recognizer: UISwipeGestureRecognizer =
   				UISwipeGestureRecognizer(target: self, action: #selector(View.swipe(_:)));
   
   			recognizer.direction = direction;
   			addGestureRecognizer(recognizer);
   		}
   



2. Create the four arrow strings with a dictionary. Add the following property to class View.

   	let arrows: [UInt: String] = [		//a dictionary
   		UISwipeGestureRecognizerDirection.Right.rawValue: "→",
   		UISwipeGestureRecognizerDirection.Left.rawValue:  "←",
   		UISwipeGestureRecognizerDirection.Up.rawValue:    "↑",
   		UISwipeGestureRecognizerDirection.Down.rawValue:  "↓"
   	];
   

   In the swipe(_:) method of class View, change

   		let direction: String;
   
   		if recognizer.direction == UISwipeGestureRecognizerDirection.Right {
   			direction = "→";
   		} else if recognizer.direction == UISwipeGestureRecognizerDirection.Left {
   			direction = "←";
   		} else if recognizer.direction == UISwipeGestureRecognizerDirection.Up {
   			direction = "↑";
   		} else if recognizer.direction == UISwipeGestureRecognizerDirection.Down {
   			direction = "↓";
   		} else {
   			direction = "unknown";
   		}
   

   to

   		var direction: String? = arrows[recognizer.direction.rawValue];
   		if direction == nil {
   			direction = "unknown";
   		}
   

   and change the subsequent use of direction to direction!.


3. We’re printing too many digits:

   start: (37.0, 213.33332824707)
   

   Make it easier to read by converting CGFloat to Float before interpolating it into the string.

   			"start: (\(Float(p.x)), \(Float(p.y))\n" +
   

   start: (37.0, 213.333)
   



4. Configure a UISwipeGestureRecognizer to call a method of some other object, for example, a method of the view controller. Remove the existing recognizer that recognizes a right swipe. Add the following method to the view controller in ViewController.swift.

   	//This method will be called automatically
   	//when the View's UISwipeGestureRecognizer recognizes a swipe.
   
   	func swipe(recognizer: UISwipeGestureRecognizer) -> Void {
   		if recognizer.direction == UISwipeGestureRecognizerDirection.Right {
   			print("Recognized a right swipe.");
   		} else {
   			print("Recognized a non-right swipe.");
   		}
   	}
   

   Add the following code to the init method of class View.

   		let application: UIApplication = UIApplication.sharedApplication();
   		let appDelegate: AppDelegate = application.delegate as! AppDelegate;
   		let viewController: ViewController = appDelegate.window!.rootViewController as! ViewController;
   
   		let recognizer: UISwipeGestureRecognizer =
   			UISwipeGestureRecognizer(target: viewController, action: #selector(ViewController.swipe(_:)));
   		recognizer.direction = UISwipeGestureRecognizerDirection.Right;
   		addGestureRecognizer(recognizer);