手势识别（三）2种添加手势方法和如何响应手势

Responding to Events with Gesture Recognizers

numberOfTapsRequired

Using Interface Builder to Add a Gesture Recognizer to Your App

@interface APLGestureRecognizerViewController ()

@property (nonatomic, strong) IBOutlet UITapGestureRecognizer *tapRecognizer;

@end

@implementation

- (IBAction)displayGestureForTapRecognizer:(UITapGestureRecognizer *)recognizer

// Will implement method later...

}

@end

Adding a Gesture Recognizer Programmatically

UIGestureRecognizer

UIPinchGestureRecognizer

addGestureRecognizer:

viewDidLoad

addGestureRecognizer: 方法来把它连接到视图。
列表1-2 创建了一个单个轻击手势识别，指定识别该手势需要一次轻击(tap)，然后把手势识别对象连接到一个视图。 通常，你在视图控制器的 
viewDidLoad 方法里创建手势识别，如列表1-2所示。


Listing 1-2  Creating a single tap gesture recognizer programmatically

列表1-2 通过程序创建一个单一的轻击手势识别

[code]- (void)viewDidLoad {
[super viewDidLoad];

// Create and initialize a tap gesture

UITapGestureRecognizer *tapRecognizer = [[UITapGestureRecognizer alloc]

initWithTarget:self action:@selector(respondToTapGesture:)];

// Specify that the gesture must be a single tap

tapRecognizer.numberOfTapsRequired = 1;

// Add the tap gesture recognizer to the view

[self.view addGestureRecognizer:tapRecognizer];

// Do any additional setup after loading the view, typically from a nib

}


Responding to Discrete Gestures
3、响应离散手势

When you create a gesture recognizer, you connect the recognizer to an action method. Use this action method to respond to your gesture recognizer’s gesture.Listing
1-3 provides an example of responding to a discrete gesture. When the user taps the view that the gesture recognizer is attached to, the view controller displays an image view that says “Tap.” The 
showGestureForTapRecognizer:
 method determines
the location of the gesture in the view from the recognizer’s
locationInView:
 property and
then displays the image at that location.

当你创建一个手势识别时，你把该识别(recognizer)连接到一个操作方法。使用该操作方法来响应手势识别的手势。列表1-3 提供了一个响应一个离散手势的例子。 当用户轻击了带有手势识别的视图时，视图控制器显示一个图像视图(image view)表示"Tap"发生。  
showGestureForTapRecognizer: 方法决定了视图中手势的位置，该位置从recognizer的locationInView: 特性中获取，然后把图片显示到该位置。


Note: The next three code examples are from the Simple
Gesture Recognizers sample code project, which you can examine for more context.
注意： 接下来的3段代码例子取自 Simple
Gesture Recognizers 样本代码工程，你可以查看它以获得更多上下文。

Listing 1-3  Handling a double tap gesture

列表1-3 处理一个双击手势

- (IBAction)showGestureForTapRecognizer:(UITapGestureRecognizer *)recognizer {

// Get the location of the gesture

CGPoint location = [recognizer locationInView:self.view];

// Display an image view at that location

[self drawImageForGestureRecognizer:recognizer atPoint:location];

// Animate the image view so that it fades out

[UIView animateWithDuration:0.5 animations:^{

self.imageView.alpha = 0.0;

}];

}

Each gesture recognizer has its own set of properties. For example, in Listing 1-4, the 
showGestureForSwipeRecognizer:
 method uses the swipe gesture recognizer’s 
direction
 property
to determine if the user swiped to the left or to the right. Then, it uses that value to make an image fade out in the same direction as the swipe.

每个手势识别都有它自己的特性集。比如，如列表1-4中，
showGestureForSwipeRecognizer: 方法使用点击(swipe)手势识别的direction 特性来决定用户是向左清扫还是向右。 然后，它使用该值来让图像从点击方向消失。


Listing 1-4  Responding to a left or right swipe gesture

列表1-4 响应一个向左或向右清扫手势

// Respond to a swipe gesture

- (IBAction)showGestureForSwipeRecognizer:(UISwipeGestureRecognizer *)recognizer {

// Get the location of the gesture

 CGPoint location = [recognizer locationInView:self.view];

// Display an image view at that location

 [self drawImageForGestureRecognizer:recognizer atPoint:location];

// If gesture is a left swipe, specify an end location

// to the left of the current location

if (recognizer.direction == UISwipeGestureRecognizerDirectionLeft) {

location.x -= 220.0;

} else {

location.x += 220.0;

}

// Animate the image view in the direction of the swipe as it fades out

 [UIView animateWithDuration:0.5 animations:^{

 self.imageView.alpha = 0.0;

self.imageView.center = location;

 }];

}


Responding to Continuous Gestures
4、响应连续手势

Continuous gestures allow your app to respond to a gesture as it is happening. For example, your app can zoom while a user is pinching or allow a user to drag an object around the screen.

连续手势允许应用程序在手势发生时响应。 比如，用户可以一边做捏合手势，一边就可以看见缩放，或者允许用户沿着屏幕拖拉一个对象。

Listing 1-5 displays a “Rotate” image at the same rotation angle as the gesture, and when the user stops rotating, animates the image so it fades out in place while rotating back to horizontal. As the
user rotates his fingers, the 
showGestureForRotationRecognizer:
 method is called continually until both fingers are lifted.

列表1-5 以跟手势同样的角度显示一个"Rotate"图片，并且当用户停止旋转时，动画该图片让其在旋转回水平方向的同时消失。 当用户旋转他的手指时，持续调用 
showGestureForRotationRecognizer: 方法直到两个手指都拿起。


Listing 1-5  Responding to a rotation gesture

列表1-5 响应一个旋转手势

// Respond to a rotation gesture

- (IBAction)showGestureForRotationRecognizer:(UIRotationGestureRecognizer *)recognizer {

// Get the location of the gesture

 CGPoint location = [recognizer locationInView:self.view];

// Set the rotation angle of the image view to

// match the rotation of the gesture

CGAffineTransform transform = CGAffineTransformMakeRotation([recognizer rotation]);

self.imageView.transform = transform;

// Display an image view at that location

 [self drawImageForGestureRecognizer:recognizer atPoint:location];

// If the gesture has ended or is canceled, begin the animation

// back to horizontal and fade out

if (([recognizer state] == UIGestureRecognizerStateEnded) || ([recognizer state] == UIGestureRecognizerStateCancelled)) {

     [UIView animateWithDuration:0.5 animations:^{

     self.imageView.alpha = 0.0;

self.imageView.transform = CGAffineTransformIdentity;

     }];

}

}

Each time the method is called, the image is set to be opaque in the 
drawImageForGestureRecognizer:
 method. When the gesture is complete, the image is set to be transparent in the 
animateWithDuration:
 method. The 
showGestureForRotationRecognizer:
 method
determines whether a gesture is complete by checking the gesture recognizer’s state. These states are explained in more detail in “Gesture
Recognizers Operate in a Finite State Machine.”

每次调用该方法时，图片都在drawImageForGestureRecognizer: 方法中被设置为不透明。 当手势完成时，图片在animateWithDuration: 方法中被设置为透明。showGestureForRotationRecognizer:方法通过检查手势识别的状态来判断手势是否完成。 关于这些状态的更多信息，请看“Gesture
Recognizers Operate in a Finite State Machine.”