贝塞尔曲线动画demo（仿美人相机效果）

效果如图：



仿美人相机，手势滑动隐藏顶部view。为了方便讲解，将屏幕分为几个区域，如图：



在拖动过程中：

1、拖动距离小于minMoveDistance，贝赛尔曲线发生形变

2、拖动大于minMoveDistance，整个view开始下移

在松开手时：

1、拖动距离小于minMoveDistance，未发生位移，贝塞尔曲线恢复形变

2、拖动大于minMoveDistance，小于minDisappearDistance，贝塞尔曲线恢复形变、位移回到初始位置。

3、拖动大于minDisappearDistance，向下移动隐藏view

一、根据y轴位移量确定贝塞尔路径

在拖动时曲线形变、松手时曲线恢复形变的时候都需要改变贝塞尔曲线，实际上是改变二阶贝塞尔曲线的控制点，因此写一个方法，根据传入的y轴位移量得到新的贝塞尔路径：

- (CGPathRef)getPathWithMoveDistance:(CGFloat)distance{

UIBezierPath *path = [UIBezierPath bezierPath];
CGPoint startPoint = CGPointMake(0, 0);
CGPoint controlPoint = CGPointMake(self.bounds.size.width*0.5, 60+distance);
CGPoint endPoint = CGPointMake(self.bounds.size.width, 0);

[path moveToPoint:startPoint];
[path addQuadCurveToPoint:endPoint controlPoint:controlPoint];

[path addLineToPoint:CGPointMake(self.bounds.size.width, self.bounds.size.height)];
[path addLineToPoint:CGPointMake(0, self.bounds.size.height)];

return path.CGPath;
}

二、初始化图形

初始化的时候，可以根据上一步的方法，传入位移量0，获取贝塞尔路径，并将获得的路径赋给CAShapeLayer：

- (id)initWithFrame:(CGRect)frame{
if (self = [super initWithFrame:frame]) {
self.originY = frame.origin.y;
[self setUpLayer];
[self addGesure];
}
return self;
}

- (void)setUpLayer{
self.topLineLayer = [CAShapeLayer layer];
self.topLineLayer.fillColor = ColorForTheme.CGColor;
self.topLineLayer.strokeColor = ColorForTheme.CGColor;
self.topLineLayer.path = [self getPathWithMoveDistance:0];
[self.layer addSublayer:self.topLineLayer];
}

三、添加手势

添加UIPanGestureRecognizer拖动手势，并处理手势拖动和结束拖动的事件。

拖动时：

1、拖动距离小于minMoveDistance，只有贝赛尔曲线发生形变，调用步奏一中的方法。

2、拖动距离大于minMoveDistance，整个view开始下移

结束拖动时：

调用revertFormY:方法，传入当前在y轴上已经发生的位移量

- (void)addGesure{
if (self.gesture == nil) {
self.gesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
}
[self addGestureRecognizer:self.gesture];
}

- (void)handlePan:(UIPanGestureRecognizer *)gesture{
CGFloat distanceX = [gesture translationInView:self].x;
CGFloat distanceY = [gesture translationInView:self].y;

if (ABS(distanceX) > ABS(distanceY)) {
return;
}
//拖动过程
if (gesture.state == UIGestureRecognizerStateChanged) {
NSLog(@"%f",distanceY);

//移动少于minMoveDistance，贝赛尔曲线形变
if (distanceY > 0 && distanceY <= minMoveDistance) {
self.topLineLayer.path = [self getPathWithMoveDistance:distanceY];
}
//移动大于minMoveDistance，整个view下移
else if (distanceY > minMoveDistance) {
self.frame = CGRectMake(0, self.originY+distanceY-minMoveDistance, self.bounds.size.width, self.bounds.size.height);
}
}
//手势结束
if (gesture.state == UIGestureRecognizerStateEnded || gesture.state == UIGestureRecognizerStateCancelled || gesture.state == UIGestureRecognizerStateFailed) {
[self removeGestureRecognizer:self.gesture];
[self revertFormY:distanceY];
}
}

四、revertFormY：恢复形变方法

根据传入的y轴上的位移量，实现不同的效果：

1、y小于minMoveDistance，未发生位移，贝塞尔曲线恢复形变

2、y大于minMoveDistance，小于minDisappearDistance，贝塞尔曲线恢复形变、位移回到初始位置。

3、y大于minDisappearDistance，向下移动隐藏view

//手势结束后恢复或隐藏
-(void)revertFormY:(CGFloat)y{

//y < 最小的隐藏位移距离，未发生位移，贝塞尔曲线恢复动画
if (y < minDisappearDistance) {
CAKeyframeAnimation *vibrate = [CAKeyframeAnimation animationWithKeyPath:@"path"];
vibrate.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
vibrate.values = @[
(id) [self getPathWithMoveDistance:y],
(id) [self getPathWithMoveDistance:-(y * 0.3)],
(id) [self getPathWithMoveDistance:(y * 0.2)],
(id) [self getPathWithMoveDistance:-(y * 0.15)],
(id) [self getPathWithMoveDistance:(y * 0.1)],
(id) [self getPathWithMoveDistance:-(y * 0.07)],
(id) [self getPathWithMoveDistance:(y * 0.05)],
(id) [self getPathWithMoveDistance:0.0]
];
vibrate.duration = 0.5;
vibrate.removedOnCompletion = NO;
vibrate.fillMode = kCAFillModeForwards;
vibrate.delegate = self;
[self.topLineLayer addAnimation:vibrate forKey:nil];
}

//y > 最小位移距离，发生了位移
if(y > minMoveDistance){
[UIView animateWithDuration:0.3 animations:^{
CGFloat endY;
//向上恢复view
if (y < minDisappearDistance) {
endY = self.originY;
}
//向下隐藏view
else{
endY = SCREEN_HEIGHT;
}
self.frame = CGRectMake(0, endY, SCREEN_WIDTH, self.frame.size.height);
}];
}
}

五、双击屏幕空白，消失的view从底部上移，恢复到初始位置

这个只是为了回到初始状态，根据实际需求实现。

//恢复到初始位置
- (void)comeBack{
if (self.frame.origin.y <= self.originY) {
return;
}

[UIView animateWithDuration:0.3 animations:^{
self.frame = CGRectMake(0, self.originY, SCREEN_WIDTH, self.frame.size.height);
} completion:^(BOOL finished) {
[self revertFormY:10];
}];
}

完整代码：https://github.com/dolacmeng/JXBezierDemo