//添加监听者

[table addObserver: self forKeyPath: @"contentOffset" options: NSKeyValueObservingOptionNew context: nil];

  

/**

 *  监听属性值发生改变时回调

 */

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

{

    CGFloat offset = table.contentOffset.y;

    CGFloat delta = offset / 1000.f;

        

    self.navigationController.navigationBar.alpha = MAX(0, delta);

}

 

//表视图滑动，调用方法执行，更改导航栏透明度