悬浮按钮

项目要求：
主界面有个悬浮按钮，可以随手指移动而移动，按钮移动停止后按钮回到屏幕边缘。

思路：
自定义一个按钮，在

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event;

方法中实现按钮位置随手指移动而移动

在

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event;

方法中实现一些动画操作

实现：

@implementation SuspensionButton

- (instancetype)init
{
    self = [super init];
    if (self) {
        self.frame = CGRectMake(0, 0, kScale(40), kScale(40));
        self.layer.cornerRadius = kScale(20);
        self.layer.masksToBounds = YES;
        self.backgroundColor = kHexColor(0x98FB98);
        self.center = CGPointMake(0, kScreenHeight/2.f);
    }
    return self;
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    [super touchesBegan:touches withEvent:event];
}

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    
    [super touchesMoved:touches withEvent:event];
    UITouch *touch = [touches anyObject];
    // 本次的触点和上次触点
    CGPoint currentPoint = [touch locationInView:self];
    CGPoint previousPonit = [touch previousLocationInView:self];
    CGPoint center = self.center;
    
    //中心点移动后的位置
    center.x += currentPoint.x - previousPonit.x;
    center.y += currentPoint.y - previousPonit.y;
    
    // 限制范围
    if (center.x > kScreenWidth - self.frame.size.width/2.f) center.x = kScreenWidth - self.frame.size.width/2.f;
    if (center.x < self.frame.size.width/2.f) center.x = self.frame.size.width/2.f;
    
    if (center.y > kScreenHeight - self.frame.size.height/2.f) center.y = kScreenHeight - self.frame.size.height/2.f;
    if (center.y < self.frame.size.height/2.f) center.y = self.frame.size.height/2.f;
    
    self.center = center;
  
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
     [super touchesEnded:touches withEvent:event];
    
    if (self.center.x < kScreenWidth/2.f) {// 回左边
        [self endAnimationWithInterPoint:CGPointMake(self.frame.size.width/2.f, self.center.y) endPoint:CGPointMake(0, self.center.y)];
    } else {// 回右边
        [self endAnimationWithInterPoint:CGPointMake(kScreenWidth - self.frame.size.width/2.f, self.center.y) endPoint:CGPointMake(kScreenWidth, self.center.y)];
    }
}

#pragma mark -- animation

- (void)endAnimationWithInterPoint:(CGPoint)interPoint  endPoint:(CGPoint)endPoint{
    /*
     dampingRatio：0~1,越小弹簧震动越明显
     velocity：初始的速度，数值越大一开始移动越快
     */
    [UIView animateWithDuration:1 delay:0 usingSpringWithDamping:0.75 initialSpringVelocity:5 options:UIViewAnimationOptionCurveEaseInOut animations:^{
        self.center = interPoint;
    } completion:^(BOOL finished) {
        
        [UIView animateWithDuration:0.5 delay:0 usingSpringWithDamping:0.8 initialSpringVelocity:1 options:UIViewAnimationOptionCurveEaseInOut animations:^{
            self.center = endPoint;
        } completion:^(BOOL finished) {
            
        }];
    }];
}

注：UITouch相关知识点可以看这篇文章https://www.jianshu.com/p/ef60a6c10a8d