iOS:How 给`tabbar` 添加阴影?

iOS:How to add shadow to`tabbar`?

我有一个测试可以为我的 tabbar 添加阴影,但它没有显示 use.My 代码如下:

    _button.layer.shadowColor = [UIColor grayColor].CGColor;
    _button.layer.shadowOffset = CGSizeMake(4,4);
    _button.layer.shadowOpacity = 0.8;
    _button.layer.shadowRadius = 4;

    /* remove tab-line */
    [[UITabBar appearance] setShadowImage:[[UIImage alloc] init]];
    [self.tabBarController.tabBar setClipsToBounds:YES];

    self.tabBarController.tabBar.layer.shadowColor = [UIColor grayColor].CGColor;
    self.tabBarController.tabBar.layer.shadowOffset = CGSizeMake(0,-4);
    self.tabBarController.tabBar.layer.shadowOpacity = 0.8;
   self.tabBarController.tabBar.layer.shadowRadius = 4;

而且我还拍了张照片证明:

创建带有阴影的图像,然后按如下方式使用。

[[UITabBar appearance] setBackgroundImage:[[UIImage alloc] INITWITHYOURCUSTOMIMAGE]]; 
[[UITabBar appearance] setShadowImage:[[UIImage alloc] INITWITHYOURCUSTOMIMAGE]];

在swift中:

UITabBar.appearance().shadowImage = UIImage(named:"YOURIMAGE")
UITabBar.appearance().backgroundImage = UIImage(named:"YOURIMAGE")