动画-CAShapeLayer实现QQ消息红点拖拽效果

CAShapeLayer

一言以蔽之：CAShapeLayer 可以根据贝塞尔曲线描绘出的路径而生成对应的图形

综合例子

• 效果图

• 关键技术点剖析

• 分析 QQ 粘性动画的关键点就是当手势拖动时候2个圆之间那个形状怎么绘制

答案：将2个圆的某一时刻之间形成的形状用数学抽象来计算。

• 拖动到超过某个范围的时候怎么执行爆炸动画

UIImageView 可以执行帧动画，类似于 Flash 效果

关键代码

- (void)pan:(UIPanGestureRecognizer *)pan{
    //当前移动的偏移量
    CGPoint transP = [pan translationInView:self];
    //改变红点的位置
    //transform并没有修改自身的 center（center 是 layer 的position），只是修改了 frame
    NSLog(@"偏移量:%@",NSStringFromCGPoint(transP));
    CGPoint center = self.center;
    center.x += transP.x;
    center.y += transP.y;
    self.center = center;

    //self.transform = CGAffineTransformTranslate(self.transform, transP.x, transP.y);
    //手势复位:设置坐标原点位上次的坐标
    [pan setTranslation:CGPointZero inView:self];

    CGFloat distance = [self distanceWith:self.smallCircle bigCircle:self];
    NSLog(@"%f",distance);


    CGFloat smallCircleRadius = self.bounds.size.width * 0.5;
    smallCircleRadius = smallCircleRadius - distance/10;

    if (smallCircleRadius < 3) {
        smallCircleRadius = 3;
    }
    self.smallCircle.bounds = CGRectMake(0, 0, smallCircleRadius*2, smallCircleRadius*2);
    self.smallCircle.layer.cornerRadius = smallCircleRadius;

    if (self.smallCircle.hidden == NO) {
        //返回一个不规则的路径
        UIBezierPath *path = [self drawTracertWithSmallCircle:self.smallCircle bigCircle:self];
        //将形状转换为一个形状图层
        self.shapeLayer.path = path.CGPath;//根据路径生成形状
    }
    //创建形状图层
    [self.superview.layer insertSublayer:self.shapeLayer atIndex:0];

    if (distance > 60) {
        self.smallCircle.hidden = YES;
        [self.shapeLayer removeFromSuperlayer];
    }

    if (pan.state == UIGestureRecognizerStateEnded) {
        //结束手势
        if (distance < 60) {
            [self.shapeLayer removeFromSuperlayer];
            self.center = self.smallCircle.center;
            self.smallCircle.hidden = NO;
        }
        else{
            //手势拖拽超过60则播放一个动画
            UIImageView *imageView = [[UIImageView alloc] initWithFrame:self.bounds];

            NSMutableArray *images = [NSMutableArray array];

            for (int i=0; i<8; i++) {
                NSString *imageName = [NSString stringWithFormat:@"%d",i+1];
                UIImage *image = [UIImage imageNamed:imageName];
                [images addObject:image];
            }
            imageView.animationImages = images;
            [imageView setAnimationDuration:1];
            [imageView startAnimating];
            [self addSubview:imageView];
            //动画结束移除本身
            dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
                [self removeFromSuperview];
            });
        }
    }

}


- (CGFloat )distanceWith:(UIView *)smallCircle bigCircle:(UIView *)bigScirle{
    CGFloat offsetX = bigScirle.frame.origin.x - smallCircle.frame.origin.x;
    CGFloat offsetY = bigScirle.frame.origin.y - smallCircle.frame.origin.y;
    return sqrt( pow(offsetX, 2) + pow(offsetY, 2));
}

//将2个圆运行的变化轨迹用代码模拟
- (UIBezierPath *)drawTracertWithSmallCircle:(UIView *)smallCircle bigCircle:(UIView *)bigCircle{

    CGFloat X1 = smallCircle.center.x;
    CGFloat X2 = bigCircle.center.x;
    CGFloat Y1 = smallCircle.center.y;
    CGFloat Y2 = bigCircle.center.y;

    CGFloat r1 = smallCircle.bounds.size.width/2;
    CGFloat r2 = bigCircle.bounds.size.width/2;

    CGFloat d = [self distanceWith:smallCircle bigCircle:bigCircle];
    //Ø 代表角度
    CGFloat SinØ = (X2 - X1)/d;
    CGFloat CosØ = (Y2 - Y1)/d;

    CGPoint pointA = CGPointMake(X1 - r1*CosØ, Y1 + r1*SinØ);

    CGPoint pointB = CGPointMake(X1 + r1*CosØ, Y1 - r1*SinØ);

    CGPoint pointC = CGPointMake(X2 + r2*CosØ, Y2 - r2*SinØ);

    CGPoint pointD = CGPointMake(X2 - r2*CosØ, Y2 + r2*SinØ);

    CGPoint pointO = CGPointMake(X1 + SinØ *d/2, Y1 + CosØ*d/2);

    CGPoint pointP = CGPointMake(X1 + SinØ *d/2,Y1 + CosØ*d/2 );

    //描述路径
    UIBezierPath *path = [UIBezierPath bezierPath];

    //AB
    [path moveToPoint:pointA];
    [path addLineToPoint:pointB];

    //BC(曲线)
    [path addQuadCurveToPoint:pointC controlPoint:pointP];

    //CD
    [path addLineToPoint:pointD];

    //DA(曲线)
    [path addQuadCurveToPoint:pointA controlPoint:pointO];

    return path;
}

完整的代码，Github地址