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(0, 0)];
    attrs[UITextAttributeFont] = [UIFont systemFontOfSize:20];

    [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(0, 0)];
    itemAttrs[UITextAttributeFont] = [UIFont systemFontOfSize:14];
    [barItem setTitleTextAttributes:itemAttrs forState:UIControlStateNormal];
}