IOS swift的动画效果及实现方法

 //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)        }            }