QQ（iOS）客户端的粘性动画效果
来自： http://www.cnblogs.com/ziyi--caolu/p/5195615.html
qq的app中要是有新的联系人发消息过来，相应联系人的cell右边会有一个红色的圆圈表示消息条数。如果去触碰那个圆圈，可以发现它竟然会跟着手指的移动而移动。
在一定范围内，手指离开屏幕，会发现红色圆圈会自动弹性的回到原来的位置。而如果超出一定距离，这个圆圈会做一个销毁的动画，从而从view上移除掉。
产品要求公司的App也要有效果，并花了些时间去学习它的实现过程，发现其实原理还是比较简单的。
（由于mac制作gif图片实在过于麻烦，所以效果只能是看看图片。）
Demo的github地址：https://github.com/wzpziyi1/QQ-Goo
这是实现过程中的一些效果图片：
经过分析，可以发现，是两个圆和一个不规则矩形位置、大小的变化。一开始，小的圆圈和大的圆圈的center是相同的，当移动大圆的时候，小圆的半径随着大圆离小圆的距离变远而变小，当大圆距离小圆一定距离时，将小圆隐藏掉，中间的不规则矩形remove掉。
那么，不规则矩形怎么表示呢？可以利用Core Graphics在drawRect方法里面绘制不规则矩形的path，然后利用颜色fill就行。不规则矩形是随着大圆的移动而不断变化的，如果在drawRect方法里面绘制，那么在移动过程中不断调用setNeedsDisplay方法进行重绘。这是种可行的方案，我所用的也大致是这种思路。
不过，我没有在drawRect方法里面绘制，而是利用了CAShapeLayer，将不规则矩形的path绘制在shapeLayer里面，这样在移动大圆的过程中不断更新CAShapeLayer的path即可。
当然，难点并在在这里。而是不规则矩形的各个点的位置。要绘制这个不规则矩形，需要知道六个点的位置：
有了这些点的坐标，那么就可以用UIBezierPath来绘制相应的路径，代码如下：
- (UIBezierPath *)pathWithBigCircleView:(UIView *)bigCircleView smallCircleView:(UIView *)smallCircleView { CGPoint bigCenter = bigCircleView.center; CGFloat x2 = bigCenter.x; CGFloat y2 = bigCenter.y; CGFloat r2 = bigCircleView.bounds.size.width / 2; CGPoint smallCenter = smallCircleView.center; CGFloat x1 = smallCenter.x; CGFloat y1 = smallCenter.y; CGFloat r1 = smallCircleView.bounds.size.width / 2; // 获取圆心距离 CGFloat d = [self distanceWithPointA:bigCenter pointB:smallCenter]; //Θ:(xita) CGFloat sinθ = (x2 - x1) / d; CGFloat cosθ = (y2 - y1) / d; // 坐标系基于父控件 CGPoint pointA = CGPointMake(x1 - r1 * cosθ , y1 + r1 * sinθ); CGPoint pointB = CGPointMake(x1 + r1 * cosθ , y1 - r1 * sinθ); CGPoint pointC = CGPointMake(x2 + r2 * cosθ , y2 - r2 * sinθ); CGPoint pointD = CGPointMake(x2 - r2 * cosθ , y2 + r2 * sinθ); CGPoint pointO = CGPointMake(pointA.x + d / 2 * sinθ , pointA.y + d / 2 * cosθ); CGPoint pointP = CGPointMake(pointB.x + d / 2 * sinθ , pointB.y + d / 2 * cosθ); UIBezierPath *path = [UIBezierPath bezierPath]; // A [path moveToPoint:pointA]; // AB [path addLineToPoint:pointB]; // 绘制BC曲线 [path addQuadCurveToPoint:pointC controlPoint:pointP]; // CD [path addLineToPoint:pointD]; // 绘制DA曲线 [path addQuadCurveToPoint:pointA controlPoint:pointO]; return path; } 在实现过程中，我是自定义UIButton的，需要注意的是，在监听button的拖动时，最好是给它添加UIPanGestureRecognizer手势，而不要在touchesBegin方法里面去判断它的移动位置，因为Touches系列方法会屏蔽button的点击。
自定义的这个button默认就是大圆，包含一个小圆(UIView)属性，但是这个小圆并不是添加在自定义的这个button（也就是大圆）里面，而是在button的superView上。因为小圆并不需要随着大圆位置的改变而改变位置，相应的，shapeLayer也是添加在button（大圆）的父控件上。
给大圆添加了pan手势，在pan:方法里面随之改变小圆的大小和绘制shapeLayer的path。
当pan手势状态为End的时候，需要判断大圆与小圆的距离有没有超出最大距离，如果超过，那么添加一个gif图片，播放销毁大圆的过程。如果没有被销毁，那么大圆需要复位，相应代码：
#import "ZYGooView.h" #define kMaxDistance 100 @interface ZYGooView () @property (nonatomic, weak) UIView *smallCircleView; @property (nonatomic, assign) CGFloat smallCircleR; @property (nonatomic, weak) CAShapeLayer *shapeLayer; @end @implementation ZYGooView - (instancetype)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { [self commitInit]; } return self; } - (void)awakeFromNib { [self commitInit]; } - (void)commitInit { self.layer.cornerRadius = self.frame.size.width * 0.5; self.layer.masksToBounds = YES; self.smallCircleR = self.frame.size.width * 0.5; self.smallCircleView.bounds = self.bounds; self.smallCircleView.center = self.center; self.smallCircleView.layer.cornerRadius = self.smallCircleView.frame.size.width * 0.5; [self addGesture]; } #pragma mark ----懒加载方法 - (UIView *)smallCircleView { if (_smallCircleView == nil) { UIView *view = [[UIView alloc] init]; view.backgroundColor = self.backgroundColor; [self.superview addSubview:view]; [self.superview insertSubview:view atIndex:0]; _smallCircleView = view; } return _smallCircleView; } - (CAShapeLayer *)shapeLayer { if (_shapeLayer == nil) { CAShapeLayer *shapeLayer = [CAShapeLayer layer]; shapeLayer.path = [self pathWithBigCircleView:self smallCircleView:self.smallCircleView].CGPath; shapeLayer.fillColor = self.backgroundColor.CGColor; [self.superview.layer addSublayer:shapeLayer]; [self.superview.layer insertSublayer:shapeLayer atIndex:0]; _shapeLayer = shapeLayer; } return _shapeLayer; } #pragma mark ----其他方法 - (void)addGesture { UIPanGestureRecognizer *recognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)]; [self addGestureRecognizer:recognizer]; } - (void)pan:(UIPanGestureRecognizer *)recognizer { CGPoint point = [recognizer translationInView:self.superview]; CGPoint center = self.center; center.x += point.x; center.y += point.y; self.center = center; //复位 [recognizer setTranslation:CGPointZero inView:self]; CGFloat distance = [self distanceWithPointA:self.smallCircleView.center pointB:self.center]; if (distance == 0) return; CGFloat newR = self.smallCircleR - distance / 15.0; NSLog(@"%f", newR); self.smallCircleView.bounds = CGRectMake(0, 0, newR * 2, newR * 2); self.smallCircleView.layer.cornerRadius = newR; if (distance > kMaxDistance || newR <= 0) { self.smallCircleView.hidden = YES; [self.shapeLayer removeFromSuperlayer]; self.shapeLayer = nil; } if (distance <= kMaxDistance && self.smallCircleView.hidden == NO) { self.shapeLayer.path = [self pathWithBigCircleView:self smallCircleView:self.smallCircleView].CGPath; } if (recognizer.state == UIGestureRecognizerStateEnded) { if (distance <= kMaxDistance) { dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.03 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ [self.shapeLayer removeFromSuperlayer]; self.shapeLayer = nil; }); [UIView animateWithDuration:0.4 delay:0 usingSpringWithDamping:0.6 initialSpringVelocity:0 options:UIViewAnimationOptionCurveLinear animations:^{ self.center = self.smallCircleView.center; } completion:^(BOOL finished) { self.smallCircleView.hidden = NO; }]; } else { UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.bounds]; [self addSubview:imageView]; NSMutableArray *images = [NSMutableArray array]; for (int i = 1; i <= 8; i++) { NSString *imageName = [NSString stringWithFormat:@"%d", i]; UIImage *image = [UIImage imageNamed:imageName]; [images addObject:image]; } imageView.animationImages = images; imageView.animationDuration = 0.6; imageView.animationRepeatCount = 1; [imageView startAnimating]; dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.5 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{ [self removeFromSuperview]; }); } } } - (CGFloat)distanceWithPointA:(CGPoint)pointA pointB:(CGPoint)pointB { CGFloat dx = pointB.x - pointA.x; CGFloat dy = pointB.y - pointA.y; return sqrt(dx * dx + dy * dy); } - (UIBezierPath *)pathWithBigCircleView:(UIView *)bigCircleView smallCircleView:(UIView *)smallCircleView { CGPoint bigCenter = bigCircleView.center; CGFloat x2 = bigCenter.x; CGFloat y2 = bigCenter.y; CGFloat r2 = bigCircleView.bounds.size.width / 2; CGPoint smallCenter = smallCircleView.center; CGFloat x1 = smallCenter.x; CGFloat y1 = smallCenter.y; CGFloat r1 = smallCircleView.bounds.size.width / 2; // 获取圆心距离 CGFloat d = [self distanceWithPointA:bigCenter pointB:smallCenter]; //Θ:(xita) CGFloat sinθ = (x2 - x1) / d; CGFloat cosθ = (y2 - y1) / d; // 坐标系基于父控件 CGPoint pointA = CGPointMake(x1 - r1 * cosθ , y1 + r1 * sinθ); CGPoint pointB = CGPointMake(x1 + r1 * cosθ , y1 - r1 * sinθ); CGPoint pointC = CGPointMake(x2 + r2 * cosθ , y2 - r2 * sinθ); CGPoint pointD = CGPointMake(x2 - r2 * cosθ , y2 + r2 * sinθ); CGPoint pointO = CGPointMake(pointA.x + d / 2 * sinθ , pointA.y + d / 2 * cosθ); CGPoint pointP = CGPointMake(pointB.x + d / 2 * sinθ , pointB.y + d / 2 * cosθ); UIBezierPath *path = [UIBezierPath bezierPath]; // A [path moveToPoint:pointA]; // AB [path addLineToPoint:pointB]; // 绘制BC曲线 [path addQuadCurveToPoint:pointC controlPoint:pointP]; // CD [path addLineToPoint:pointD]; // 绘制DA曲线 [path addQuadCurveToPoint:pointA controlPoint:pointO]; return path; } @end Demo的github地址：https://github.com/wzpziyi1/QQ-Goo
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