iOS 实现点赞动画特效

动画的基本使用

动画的实现基本上是基于对View控件和View的layer属性进行操作，对视图进行移动，尺寸变换，透明度变换，旋转等一系列操作。
关键帧动画：
动画的实现可以分为两个部分，一部分是规定动画的变化内容，比如view需要把scale从0变化到1，这个数字是相对值，即从尺寸为0变化到正常尺寸。另一个部分是规定动画的渐变时间。这样就实现了view在规定时间完成指定变化了，这个变化的过程也可以通过参数设置为非均匀变化的。上面的示例是关键帧动画的实现，实现的方式是把动画划分为几个部分，“第一帧”做一件事，“第二帧”再做另外一件事，这就使得变化连续且可控。Duration参数确定了时间，delay确定了延时多久执行，options确定了关键帧动画布局子控件。completion的参数是一个block，其中的内容是在内容执行结束后才调用。这里做了3帧，前两帧做了尺寸变为3倍然后恢复，后一帧使得其隐藏。结束后会调用block使其移除。

[UIView animateKeyframesWithDuration:self.animationDurtion * 4 delay:0.0 options:UIViewKeyframeAnimationOptionLayoutSubviews animations:^{
            /*参数1:关键帧开始时间
              参数2:关键帧占用时间比例
              参数3:到达该关键帧时的属性值 */
            [UIView addKeyframeWithRelativeStartTime:0.0 relativeDuration:0.5 * self.animationDurtion animations:^{
                giveLikeView.transform =  CGAffineTransformMakeScale(3, 3);;
            }];
            [UIView addKeyframeWithRelativeStartTime:0.5 * self.animationDurtion relativeDuration:0.5 * self.animationDurtion animations:^{
                giveLikeView.transform = CGAffineTransformIdentity;
            }];
            [UIView addKeyframeWithRelativeStartTime:self.animationDurtion relativeDuration:self.animationDurtion * 3 animations:^{
                giveLikeView.alpha = 0;
            }];
        } completion:^(BOOL finished) {
            giveLikeView.hidden = YES;
            [giveLikeView removeFromSuperview];
        }];

CAShapeLayer和UIBezierPath：
当不满足于view的变化，还需要在view的表面绘制一些图案，就要对layer进行操作，layer可以理解为是view的表面，每个view都有layer参数。UIBezierPath是贝塞尔曲线，它用于设置绘图的路径，没有了它，layer的绘制也是无效的，因为没有边界呀。
如下代码绘制了一个圆形的曲线，设置了它的中心，半径，起始终止角这些属性。

   UIBezierPath *bezierPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(giveLikeView.bounds.size.width/2, giveLikeView.bounds.size.height/2) radius:giveLikeView.bounds.size.width startAngle:-1.57 endAngle:-1.57+3.14*2 clockwise:YES];
    circleLayer.path = bezierPath.CGPath;
    [self.layer addSublayer:circleLayer];

在最后我们可以看到：circleLayer.path = bezierPath.CGPath; [self.layer addSublayer:circleLayer];
它的作用是设置layer的路径，并把layer添加到view的表面。下面来看看layer的配置。
创建一个layer后设置它的frame和颜色以及边界，线宽这些属性。

    CAShapeLayer *circleLayer = [[CAShapeLayer alloc] init];
    circleLayer.frame = giveLikeView.frame;
    circleLayer.fillColor = [UIColor clearColor].CGColor;
    circleLayer.strokeColor = [UIColor redColor].CGColor;
    circleLayer.lineWidth = 1;

几处联系：把贝塞尔曲线和layer联系起来，把layer和view的layer联系起来。
为layer加动画（动画组）：
先创建动画组CAAnimationGroup，它可以容纳若干动画，然后创建若干CABasicAnimation基础动画。分别设置属性，动画组需要涉及的属性有时间功能，kCAMediaTimingFunctionEaseIn表示逐渐加快，另外还有设置持续时间，设置kCAFillModeForwards表示动画在结束后会保持，removedOnCompletion = NO表示最后不移除。在基础动画的设置中，一般设置在动画组中的起始时间和持续时间，还有参数的变化。最后的 group.animations = @[scaleAnimtion,widthStartAnimtion,widthEndAnimtion];[circleLayer addAnimation:group forKey:nil];
两句表示在动画组中添加动画然后为layer添加动画组，这样layer就有动画特效了。

    //动画
    CAAnimationGroup *group = [CAAnimationGroup animation];
    group.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
    NSTimeInterval groupInterval = self.animationDurtion * 0.8;
    group.duration = groupInterval;
    group.fillMode = kCAFillModeForwards;
    group.removedOnCompletion = NO;
    
    CABasicAnimation * scaleAnimtion = [CABasicAnimation animationWithKeyPath:@"transform.scale"];
    scaleAnimtion.beginTime = 0;
    scaleAnimtion.duration = groupInterval * 0.8;
    scaleAnimtion.fromValue = @(0);
    scaleAnimtion.toValue = @(1);
    
    CABasicAnimation * widthStartAnimtion = [CABasicAnimation animationWithKeyPath:@"lineWidth"];
    widthStartAnimtion.beginTime = 0;
    widthStartAnimtion.duration = groupInterval * 0.8;
    widthStartAnimtion.fromValue = @(1);
    widthStartAnimtion.toValue = @(2);
    
    CABasicAnimation * widthEndAnimtion = [CABasicAnimation animationWithKeyPath:@"lineWidth"];
    widthEndAnimtion.beginTime = groupInterval * 0.8;
    widthEndAnimtion.duration = groupInterval * 0.2;
    widthEndAnimtion.fromValue = @(2);
    widthEndAnimtion.toValue = @(0);
    
    group.animations = @[scaleAnimtion,widthStartAnimtion,widthEndAnimtion];
    [circleLayer addAnimation:group forKey:nil];

点赞动画的实现原理

下面来介绍demo的实现原理。
controller的尺寸设置为全屏，在其上方也覆盖一个全屏的view，再在view上添加点击事件（手势）。

- (void)addGesture
{
    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(creatOneHeart:)];
    [self addGestureRecognizer:tap];    
}

下面看看点击后调用的方法：
这里每次点击都会获取点击的位置然后去初始化一个爱心，这是异步任务，放在主队列中执行。

- (void)creatOneHeart:(UITapGestureRecognizer *)sender
{
    CGPoint point = [sender locationInView:self];
    dispatch_async(dispatch_get_main_queue(),^{
        [self initOneNewHeart:point];
    });
}

这段代码创建了视图对象，这里自然用到了事先创建好的心形图片。这里把创建的imageview存到队列，显示到view上，最后调用likeAction:方法执行动画。

- (UIImageView *)createGiveLikeView
{
    UIImageView *giveLikeView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];
    giveLikeView.backgroundColor = [UIColor clearColor];
    UIImage *image = [UIImage imageNamed:@"icon_home_like_after"];
    giveLikeView.userInteractionEnabled = YES;
    giveLikeView.tag = GiveType;
    giveLikeView.image = image;
    giveLikeView.hidden = NO;
    _giveLikeView = giveLikeView;
    return _giveLikeView;
}
- (void)initOneNewHeart:(CGPoint)point
{
    UIImageView *giveLikeView = [self createGiveLikeView];
    giveLikeView.center = point;
    [self.array addObject:giveLikeView];
    [self addSubview:giveLikeView];
    [self likeAction:giveLikeView];
}

我们看看giveLikeAction：这个方法，它包括执行心形的变化动画和绘制六个辐射的三角形动画，还有辐散的圆的动画。

- (void)likeAction:(UIImageView *)giveLikeView
{
    [self giveLikeAction:giveLikeView];
}
- (void)giveLikeAction:(UIImageView *)giveLikeView
{
    [self animtionChangeLikeType:giveLikeView];
    [self createTrigonsAnimtion:giveLikeView];
    [self createCircleAnimation:giveLikeView];
}

接下来直接看看辐散的三角形的动画（爱心的变化动画在上面已经涉及到了）：
这段代码跑了6个循环，做了6个三角形，它们分别有动画效果。
shape.transform = CATransform3DMakeRotation(3.14 / 3 * i, 0, 0, 1);实现了旋转。
[giveLikeView.layer addSublayer:shape];执行layer的添加。
因为在循环中，每个layer都有独立的动画，动画组实现的效果是三角形从小变大，最后变成一条直线并消失。
下面的两行代码用到了__bridge，它的作用是实现类型的转换，这里把CGPathRef类型“桥接”转化为了id类型，如果没有它，会报错。
pathAnimation.fromValue = (__bridge id)startPath.CGPath;
pathAnimation.toValue = (__bridge id)endPath.CGPath;

- (void)createTrigonsAnimtion:(UIImageView *)giveLikeView
{
    for(int i=0;i<6;i++) {
        //创建一个layer并设置位置和填充色
        CAShapeLayer *shape = [[CAShapeLayer alloc] init];
        shape.position = CGPointMake(giveLikeView.bounds.size.width/2, giveLikeView.bounds.size.height/2);
        shape.fillColor = [UIColor redColor].CGColor;
        //设置贝塞尔曲线，执行路径
        UIBezierPath *startPath = [[UIBezierPath alloc] init];
        [startPath moveToPoint:CGPointMake(-2, 30)];
        [startPath addLineToPoint:CGPointMake(2, 30)];
        [startPath addLineToPoint:CGPointMake(0, 0)];
        [startPath addLineToPoint:CGPointMake(-2, 30)];
        shape.path = startPath.CGPath;
        
        //旋转
        shape.transform = CATransform3DMakeRotation(3.14 / 3 * i, 0, 0, 1);
        [giveLikeView.layer addSublayer:shape];
        
        //动画组
        CAAnimationGroup *groupAnimation = [CAAnimationGroup animation];
        groupAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
        groupAnimation.duration = self.animationDurtion;
        groupAnimation.fillMode = kCAFillModeForwards;
        groupAnimation.removedOnCompletion = NO;
        
        //基础动画1
        CABasicAnimation *scaleAnimtion = [CABasicAnimation animationWithKeyPath:@"transform.scale"];
        //缩放时间占20%
        scaleAnimtion.duration = self.animationDurtion * 0.2;
        scaleAnimtion.fromValue = @(0);
        scaleAnimtion.toValue = @(1);

        //绘制三角形结束 一条直线
        UIBezierPath *endPath = [UIBezierPath bezierPath];
        [endPath moveToPoint:CGPointMake(-2, 30)];
        [endPath addLineToPoint:CGPointMake(2, 30)];
        [endPath addLineToPoint:CGPointMake(0, 30)];

        //基础动画2
        CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"path"];
        pathAnimation.beginTime = self.animationDurtion * 0.2;
        pathAnimation.duration = self.animationDurtion * 0.8;
        pathAnimation.fromValue = (__bridge id)startPath.CGPath;
        pathAnimation.toValue = (__bridge id)endPath.CGPath;

        groupAnimation.animations = @[scaleAnimtion,pathAnimation];
        [shape addAnimation:groupAnimation forKey:nil];
    }
}

demo实现的动画效果

demo的GitHub链接

最后附上demo链接：MYFGiveLikeAnimationDemo