iOS 自定义各类bar的属性

　　在iOS应用开发中，经常需要为导航栏和标签栏设置相同的主题，一个一个去设置的话，就太麻烦了，可以通过对应用中所有的导航栏和标签栏同意设置背景、字体等属性。

　　如：创建一个继承自“UINavigationController”的公共父类，然后应用中所有的NavigationController都继承UINavigationController，通过在UINavigationController类中的类方法

initialize中对导航栏属性进行设置，就会对项目中所有的导航栏控制器起作用

　　示例代码如下：

 + (void)initialize
 {

 #warning  可以通过设置UITabBar主题的方式来修改UITabBar中按钮的颜色
     UITabBar *tabBar = [UITabBar appearance];
     NSMutableDictionary *tabAttrs = [NSMutableDictionary dictionary];
     tabAttrs[UITextAttributeTextColor] = [UIColor orangeColor];
     [tabBar setTintColor:[UIColor orangeColor]];

     // 1 设置UINavigationBar
     UINavigationBar *navBar = [UINavigationBar appearance];

     //1.1 设置状态栏
     [UIApplication sharedApplication].statusBarStyle = UIStatusBarStyleBlackOpaque;

     //1.2 设置背景图片
         [navBar setBackgroundImage:[UIImage imageWithName:@"navigationbar_background"] forBarMetrics:UIBarMetricsDefault];

     //1.3.设置字体
     NSMutableDictionary *attrs = [NSMutableDictionary dictionary];
     attrs[UITextAttributeTextColor] = [UIColor blackColor];
     attrs[UITextAttributeTextShadowOffset] = [NSValue valueWithCGSize:CGSizeMake(, )];
     attrs[UITextAttributeFont] = [UIFont systemFontOfSize:];

     [navBar setTitleTextAttributes:attrs];

     //2 设置导航条按钮主题
     UIBarButtonItem *barItem = [UIBarButtonItem appearance];
     //2.1 设置背景图
     [barItem setBackButtonBackgroundImage:[UIImage imageWithName:@"navigationbar_button_background"] forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
     [barItem setBackButtonBackgroundImage:[UIImage imageWithName:@"navigationbar_button_background_pushed"] forState:UIControlStateHighlighted barMetrics:UIBarMetricsDefault];
     [barItem setBackButtonBackgroundImage:[UIImage imageWithName:@"navigationbar_button_background_disable"] forState:UIControlStateDisabled barMetrics:UIBarMetricsDefault];
     //2.2 设置字体属性
     NSMutableDictionary *itemAttrs = [NSMutableDictionary dictionary];

     itemAttrs[UITextAttributeTextColor] = iOS7 ? [UIColor orangeColor] : [UIColor blackColor];
     itemAttrs[UITextAttributeTextShadowOffset] = [NSValue valueWithCGSize:CGSizeMake(, )];
     itemAttrs[UITextAttributeFont] = [UIFont systemFontOfSize:];
     [barItem setTitleTextAttributes:itemAttrs forState:UIControlStateNormal];
 }