学习笔记:UIPanGestureRecognizer

UIPanGestureRecognizer实现左右滑动
1.添加手势和观察者
// 添加pan手势
[self.view addGestureRecognizer:[[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)]];

// 添加观察者监听oneView的frame的改变
[self.oneView addObserver:self forKeyPath:@"frame" options:NSKeyValueObservingOptionOld context:nil];

2.监听手势和观察者
// 监听观察者

• (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context
  {
  if (self.oneView.frame.origin.x > 0) {
  self.threeView.hidden = YES;
  }else if (self.oneView.frame.origin.x < 0)
  {
  self.threeView.hidden = NO;
  }
  }

• (void)dealloc
  {
  NSLog(@"移除");
  [self.oneView removeObserver:self forKeyPath:@"frame"];
  }
  // 监听手势

• (void)pan:(UIPanGestureRecognizer *)pan
  {
  // 获取手势移动的位置 self.view:规定区域
  CGPoint point = [pan translationInView:self.view];
  // 获取位置水平的偏移量
  CGFloat offsetX = point.x;
  // 改变oneView的frame
  self.oneView.frame = [self frameWithOffsetX:offsetX];

  // 复位 否则pan的偏移量会递增
  [pan setTranslation:CGPointZero inView:self.view];

// 判断拖动结束的时候
if (pan.state == UIGestureRecognizerStateEnded) {
    CGFloat target = 0;
    if (self.oneView.frame.origin.x > [UIScreen mainScreen].bounds.size.width * 0.5) {
        target = self.view.bounds.size.width * 0.2;
    }
    // 获取x偏移量
    CGFloat constant = self.view.bounds.size.width - target;
    // 便宜
    self.oneView.frame = target == 0 ? self.view.bounds : CGRectMake(constant, 0, self.view.bounds.size.width, self.view.bounds.size.height);
    
}

}