iOS 使用手势UIGestureRecognizer对图像进行缩放、移动、旋转等操作

UIGestureRecognizer 类

该类拥有一系列子类，每个子类都用于识别某类指定的手势。它们是：

• UITapGestureRecognizer – “轻击”手势。可以配置为“单击”和“连击”的识别。
• UIPinchGestureRecognizer –“捏合”手势。该手势通常用于缩放视图或改变可视组件的大小。
• UIPanGestureRecognizer – “平移”手势。识别拖拽或移动动作。
• UISwipeGestureRecognizer – “轻扫”手势。当用户从屏幕上划过时识别为该手势。可以指定该动作的方向（上、下、左、右）。
• UIRotationGestureRecognizer – “转动”手势。用户两指在屏幕上做相对环形运动。
• UILongPressGestureRecognizer – “长按”手势。使用一指或多指触摸屏幕并保持一定时间。

这些手势识别器必需和视图通过addGestureRecognizer:方法联系在一起。识别器必需指定一个响应方法以便发生指定手势时进行调用。removeGestureRecognizer:方法可以将识别器从视图中移出，方法参数指定要移除的识别器。

下面通过一个实例程序来分别介绍这些手势，在一个视图中增加一个UIImageView控件，添加一个图像。对图像的操作都基于此视图中进行。分别对这个图像使用这些手势。

一、首先在一个视图中添加一个imageview控件，用以添加一个图像。

    self.productImageView.image = [UIImage imageNamed:@"iPhone.jpg"];

二、tap 手势 （轻击）

说明：在单击中，实现的是视图恢复，在双击中实现的是视图放大/缩小一倍。

//轻点
    
    // 单击
    UITapGestureRecognizer *SingleTapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(resetImage:)];
    SingleTapGesture.numberOfTapsRequired = 1;//tap次数
    [self.view addGestureRecognizer:SingleTapGesture];
    // 双击
    UITapGestureRecognizer *doubleTapGesture;
    doubleTapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleDoubleTapFrom)];
    doubleTapGesture.numberOfTapsRequired = 2; 
    [self.view addGestureRecognizer:doubleTapGesture];
    // 关键在这一行，如果双击确定偵測失败才會触发单击
    [SingleTapGesture requireGestureRecognizerToFail:doubleTapGesture];

响应方法

//单击恢复视图
- (void)resetImage:(UITapGestureRecognizer *)recognizer
{
    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.3];
    // 恒等变换. beginAnimation 和 commitAnimation 间的操作为动画过程
    self.productImageView.transform = CGAffineTransformIdentity;
    [self.productImageView setCenter:CGPointMake(self.view.frame.size.height/2, self.view.frame.size.width/2)];
    [UIView commitAnimations];
}

//双击实现放大和缩小一倍
- (void) handleDoubleTapFrom {
    if (flag == YES) {
        [UIView beginAnimations:nil context:nil];
        [UIView setAnimationDuration:0.3];
        
        [self.productImageView setFrame:CGRectMake(
                                                   self.productImageView.frame.origin.x -self.productImageView.frame.size.width / 2,
                                                   self.productImageView.frame.origin.y - self.productImageView.frame.size.height / 2,
                                                   2 * self.productImageView.frame.size.width,
                                                   2 * self.productImageView.frame.size.height)];
        [UIView commitAnimations];
        flag = NO;
    }
    else {
        [UIView beginAnimations:nil context:nil];
        [UIView setAnimationDuration:0.3];
        [self.productImageView setFrame:CGRectMake(self.productImageView.frame.origin.x+self.productImageView.frame.size.width/4, self.productImageView.frame.origin.y + self.productImageView.frame.size.height/4, self.productImageView.frame.size.width/2, self.productImageView.frame.size.height/2)];
        [UIView commitAnimations];
        flag = YES;
    }
}

特别说明这个语句：

[SingleTapGesture requireGestureRecognizerToFail:doubleTapGesture];

有些手势其实是互相关联的，例如 Tap 与 LongPress、Swipe与 Pan，或是 Tap 一次与Tap 兩次。当一個 UIView 同时添加兩个相关联的手势时，到底我这一下手指头按的要算是 Tap 还是 LongPress？如果照预设作法来看，只要先满足条件的就会跳出并呼叫对应方法，举例来说，如果同时注册了 Pan 和 Swipe，只要手指头一移动就会触发 Pan 然后跳出，因而永远都不會发生 Swipe；单点与双点的情形也是一样，永远都只会触发单点，不會有双点。

那么这个问题有解吗？答案是肯定的，UIGestureRecognizer 有个方法叫做requireGestureRecognizerToFail，他可以指定某一个 recognizer，即便自己已经满足條件了，也不會立刻触发，会等到该指定的 recognizer 确定失败之后才触发。

二、pinch 手势 （捏合缩放）

说明：在模拟器中 按住alt+鼠标左键即可出现双指触摸屏幕。

//捏合缩放
    UIPinchGestureRecognizer *pinchGesture = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchView:)];
    [self.view addGestureRecognizer:pinchGesture];  

响应方法 （以下提供了两种缩放响应方法）

// 处理捏合缩放手势
- (void) pinchView:(UIPinchGestureRecognizer *)pinchGestureRecognizer
{
    UIView *view = self.productImageView;
    if (pinchGestureRecognizer.state == UIGestureRecognizerStateBegan || pinchGestureRecognizer.state == UIGestureRecognizerStateChanged) {
        view.transform = CGAffineTransformScale(view.transform, pinchGestureRecognizer.scale, pinchGestureRecognizer.scale);
        pinchGestureRecognizer.scale = 1;
    }
}

- (void)scaleImage:(UIPinchGestureRecognizer *)recognizer 
{
	if([recognizer state] == UIGestureRecognizerStateEnded) {
        // 如果Pinch 手势结束，重置 previousScale 为 1.0
		self.previousScale = 1.0;
		return;
	}
    CGFloat newScale = [recognizer scale]-self.previousScale +1.0;
    CGAffineTransform currentTransformation = self.productImageView.transform;
    // CGAffineTransformScale(currentTransformation, 1, 1) 变换保持原大小
	CGAffineTransform newTransform = CGAffineTransformScale(currentTransformation, newScale, newScale);
    // perform the new transform
    self.productImageView.transform = newTransform;
    self.previousScale = [recognizer scale];
}

三、pan 手势 （平移）

 //平移
    UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panView:)];
    [panGesture setMinimumNumberOfTouches:1];
	[panGesture setMaximumNumberOfTouches:1];
    [self.view addGestureRecognizer:panGesture];

响应方法

// 处理拖拉手势
- (void) panView:(UIPanGestureRecognizer *)panGestureRecognizer
{
    UIView *view = self.productImageView;
    if (panGestureRecognizer.state == UIGestureRecognizerStateBegan || panGestureRecognizer.state == UIGestureRecognizerStateChanged) {       
        CGPoint translation = [panGestureRecognizer translationInView:view.superview];        
        [view setCenter:(CGPoint){view.center.x + translation.x, view.center.y + translation.y}];       
        [panGestureRecognizer setTranslation:CGPointZero inView:view.superview];
    }
}

四、rotate 手势 （旋转）

//旋转
    UIRotationGestureRecognizer *rotationGesture = [[UIRotationGestureRecognizer alloc] initWithTarget:self action:@selector(rotateView:)];
    [self.view addGestureRecognizer:rotationGesture];    

响应方法

// 处理旋转手势
- (void) rotateView:(UIRotationGestureRecognizer *)rotationGestureRecognizer
{
    UIView *view = self.productImageView;
    if (rotationGestureRecognizer.state == UIGestureRecognizerStateBegan || rotationGestureRecognizer.state == UIGestureRecognizerStateChanged) {       
        view.transform = CGAffineTransformRotate(view.transform, rotationGestureRecognizer.rotation);        
        [rotationGestureRecognizer setRotation:0];
    }
}

最后还有一个要处理的就是模拟器的横向摆放。

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return ((interfaceOrientation == UIInterfaceOrientationLandscapeRight) || (interfaceOrientation == UIInterfaceOrientationLandscapeLeft));
}