展示效果

实现效果

实现思路

1. 2个圆（一个是固定圆，一个是可拖动的圆）
2. 贝塞尔画形状
3. 拖动的时候固定圆的比例是缩小的
4. 到一定距离的时候会断开
5. 松开手势就会回弹到原地

事前准备工作

• 属性的创建

@property (nonatomic, strong) UIView *view1;
@property (nonatomic, strong) UIView *view2;
@property (nonatomic, strong) CAShapeLayer *shapeLayer;
@property (nonatomic, assign) CGPoint oldViewCenter;
@property (nonatomic, assign) CGRect oldViewFram;
@property (nonatomic, assign) CGFloat r1;

• 核心代码

- (void)setup{
    UIView *view1 = [[UIView alloc] initWithFrame:CGRectMake(CGRectGetWidth(self.view.bounds) / 2, CGRectGetHeight(self.view.bounds) * 1/9, 40, 40)];
    view1.backgroundColor = [UIColor redColor];
    view1.layer.cornerRadius = 20;
    _view1 = view1;
    [self.view addSubview:view1];
    
    UIView *view2 = [[UIView alloc] initWithFrame:_view1.frame];
    view2.backgroundColor = [UIColor redColor];
    view2.layer.cornerRadius = 20;
    _view2 = view2;
    [self.view addSubview:view2];
    
    //添加label
    UILabel *numL = [[UILabel alloc] initWithFrame:_view2.bounds];
    numL.text = @"66";
    numL.textAlignment = NSTextAlignmentCenter;
    numL.textColor = [UIColor whiteColor];
    [_view2 addSubview:numL];
    
    //添加手势
    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panAction:)];
    [_view2 addGestureRecognizer:pan];
    
    //实例化CAShapeLayer
    _shapeLayer = [CAShapeLayer layer];
    _shapeLayer.fillColor = [UIColor redColor].CGColor;
//    [self.view.layer addSublayer:_shapeLayer];

    _oldViewFram = _view1.frame;
    _oldViewCenter = _view1.center;
    _r1 = CGRectGetWidth(_view1.frame)/2;
}

• 避坑指南

1. 需要保存原先中心点的位置
2. 需要保存原先圆的大小，因为在断开的时候需要回到原来的样子
3. shapeLayer 是直接初始化添加，在拖拽中改变path就可以了

• 根据手势判断处理移动View属性状态

- (void)panAction:(UIPanGestureRecognizer *)ges{
    if (ges.state == UIGestureRecognizerStateChanged) {
        //view2跟着移动
        _view2.center = [ges locationInView:self.view];
        //
        if (_r1 < wift
            _view1.hidden = YES;
            [_shapeLayer removeFromSuperlayer];
        }else{
            //计算出6个关键点，然后画贝塞尔曲线
            [self caculPoint];
        }
       
    }else if (ges.state == UIGestureRecognizerStateFailed || ges.state == UIGestureRecognizerStateEnded || ges.state == UIGestureRecognizerStateCancelled){
        [_shapeLayer removeFromSuperlayer];
        [UIView animateWithDuration:.5 delay:0 usingSpringWithDamping:.3 initialSpringVelocity:0 options:UIViewAnimationOptionCurveEaseOut animations:^{
            _view2.center = _oldViewCenter;
        } completion:^(BOOL finished) {
            _view1.hidden = NO;
            _r1 = _oldViewFram.size.width/2;
            _view1.frame = _oldViewFram;
            _view1.layer.cornerRadius = _r1;
        }];
    }
}

• 避坑指南

1. 因为在结束动画之后会需要很多点的复原问题，所以我们在开始的时候就需要记录
2. [_shapeLayer removeFromSuperlayer]; 在取消和结束的时候还是需要移除layer的
   不然会出现画的红色背景还在的情况
3. usingSpringWithDamping 弹簧阻力效果

• 计算拖拽中的关键点

- (void)caculPoint{
    //1.求出2个中心点
    CGPoint center1 = _view1.center;
    CGPoint center2 = _view2.center;
    //2.计算2个中心点的距离
    CGFloat dis = sqrtf((center1.x - center2.x)*(center1.x - center2.x) + (center1.y - center2.y)*(center1.y - center2.y));
    //3.计算正弦余弦
    CGFloat sin = (center2.x - center1.x) / dis;
    CGFloat cos = (center1.y - center2.y) / dis;
    //4.计算半径
    CGFloat r1 = CGRectGetWidth(_oldViewFram)/2 - dis/20;
    CGFloat r2 = CGRectGetWidth(_view2.bounds)/2;
    _r1 = r1;
    NSLog(@"%f",r1);
    //5.计算6个关键点
    CGPoint pA = CGPointMake(center1.x - cos*r1, center1.y - sin*r1);
    CGPoint pB = CGPointMake(center1.x + cos*r1, center1.y + sin*r1);
    CGPoint pD = CGPointMake(center2.x - cos*r2, center2.y - sin*r2);
    CGPoint pC = CGPointMake(center2.x + cos*r2, center2.y + sin*r2);
    CGPoint pP = CGPointMake(pB.x + dis/2*sin, pB.y - dis/2*cos);
    CGPoint pO = CGPointMake(pA.x + dis/2*sin, pA.y - dis/2*cos);
    //6.画贝塞尔曲线
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:pA];
    [path addQuadCurveToPoint:pD controlPoint:pO];
    [path addLineToPoint:pC];
    [path addQuadCurveToPoint:pB controlPoint:pP];
    [path closePath];
    //7.修改_shapeLayer的path
    _shapeLayer.path = path.CGPath;
    [self.view.layer insertSublayer:_shapeLayer below:_view2.layer];

    //8.重新设置view的大小
    _view1.center = _oldViewCenter;
    _view1.bounds = CGRectMake(0, 0, _r1*2, _r1*2);
    _view1.layer.cornerRadius = _r1;
}

• 避坑指南

1. CGRectGetWidth(_oldViewFram)/2 - dis/20; 这里再次设置宽度的时候需要用到原先的那个值，不然r1的值就会有问题

• 关键点计算图示

6个关键点计算说明（ABCDOP）