//点击屏幕的事件   
       override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {   
           //自定义动画效果   
           func anim(){   
               img1.alpha=0.1   
               img1.center=CGPoint(x: 0.0, y: 0.0)   
           }   
           func completion(v:Bool){   
               println("anim completion\(v):\(falg)")   
           }   
              
           UIView.transitionWithView(img1, duration: 1.0, options: UIViewAnimationOptions.TransitionNone, animations: anim, completion: completion)   
              
              
             //视图动画效果 3步  1：开始动画 2:配置动画  3:提交动画   
             UIView.beginAnimations(nil, context: nil)   
             UIView.setAnimationTransition(UIViewAnimationTransition.CurlDown, forView: img1, cache: true)   
             UIView.setAnimationDuration(1.0)   
             UIView.commitAnimations()   
              
              
           //视图的切换   
              
           if falg{   
               falg=false   
               /*视图切换  
               fromView 开始视图  
               toView 结束视图  
               duration 效果时间  
               options 动画效果模式  
               completion 回调方法  
               */   
               UIView.transitionFromView(img2, toView: img1, duration: 1.0, options: UIViewAnimationOptions.TransitionFlipFromRight, completion: completion)   
           }else{   
               falg=true   
               UIView.transitionFromView(img1, toView: img2, duration: 1.0, options: UIViewAnimationOptions.TransitionFlipFromLeft, completion: completion)   
           }   
              
       }