IOS全局修改NavigateBar Back Button样式的两种方法：
1，通过[UIBarButtonItem appearance] 的setBackButtonBackgroundImage方法对back按钮样式自定义 但是此方法中设置forState:UIControlStateHighlighted属性无效 设置图片的imageWithRenderingMode阻止系统渲染也没有用（如有错误还望指正）
2，通过自定义NavigationController 重写push方法实现对back按钮的全局修改 当需要在局部控制器设置back 按钮样式时 直接可以覆盖 （推荐此方法）
下面是两种方法的具体实现
1，
UIImage*backButtonBackgroundImage = [UIImageimageNamed:@"navigationbar_back"];
UIImage*backButtonBackgroundImageSelected =[UIImageimageNamed:@"navigationbar_back_highlighted"];
backButtonBackgroundImage = [backButtonBackgroundImageresizableImageWithCapInsets：UIEdgeInsetsMake（0，backButtonBackgroundImage.size.width-1,0,0）];
//设置全局属性
idappearance = [UIBarButtonItem appearance];
[appearancesetBackButtonBackgroundImage:backButtonBackgroundImage forState:UIControlStateNormalbarMetrics:UIBarMetricsDefault];
[appearance setBackButtonBackgroundImage:backButtonBackgroundImageSelected forState:UIControlStateHighlighted bar Metrics:UIBarMetricsDefault];
//将文字隐藏
[appearance setTitleTextAttributes:@{
NSFontAttributeName:[UIFontsystemFontOfSize:0.1],
NSForegroundColorAttributeName: [UIColorclearColor]
}
forState:UIControlStateNormal];
2（推荐此方法）
//首先创建自定义UICustomNavigationController 继承系统的UINavigationController
//重写UICustomNavigationController 的 -(void)pushViewController:(UIViewController*)viewController animated:(BOOL)animated 方法：
@implementation UICustomNavigationController
-(void)pushViewController:(UIViewController*)viewController animated:(BOOL)animated{
[superpushViewController:viewControlleranimated:animated];
//NavigationController中包含的第一个UIViewController也是push方法进来的 但是一般这个controller不需要添加back button
if(self.viewControllers.count>1) {
UIButton*backButton=[UIButtonbuttonWithType:UIButtonTypeCustom];
[backButtonsetBackgroundImage:[UIImageimageNamed:@"navigationbar_back"]forState:UIControlStateNormal];
[backButtonsetBackgroundImage:[UIImageimageNamed:@"navigationbar_back_highlighted"]forState:UIControlStateHighlighted];
backButton.frame=CGRectMake(0,0,30,30);
[backButtonaddTarget:selfaction:@selector(back)forControlEvents:UIControlEventTouchUpInside];
viewController.navigationItem.leftBarButtonItem=[[UIBarButtonItemalloc]initWithCustomView:backButton];
}
}
//back方法
-(void)back{
[self popViewControllerAnimated:YES];
}
@end
最后创建自定义Back 按钮的UICustomNavigationController
UICustomNavigationController*navVc=[[UICustomNavigationController alloc] initWithRootViewController:childViewController];
