UINavigationController 默认返回按钮 处理

之前写过一个处理这个玩意儿的文章，主要是设置返回按钮的文字和图片，今天介绍一个新做法，几个api自行谷歌，我就直接上代码了

为了方便，定义两个类型

typedef void(^PushBlock)(UINavigationController* self, UIViewController* viewController, BOOL animated);
typedef void(*PushIMP)(id, SEL, UIViewController*, BOOL);

定义一个拦截函数（私有）

/**
 拦截 -[UINavigationController pushViewController:animated:]

 @param push block代码块
 */
static void intercept_push(PushBlock push)
{
    static PushBlock will_push;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class nvc_class = [UINavigationController class];
        SEL push_sel = @selector(pushViewController:animated:);
        Method push_method = class_getInstanceMethod(nvc_class, push_sel);
        PushIMP push_imp = (PushIMP)method_getImplementation(push_method);
        IMP push_block = imp_implementationWithBlock(^(UINavigationController* self, UIViewController* viewController, BOOL animated) {
            if (will_push) {
                will_push(self, viewController, animated);
            }
            push_imp(self, push_sel, viewController, animated);
        });
        class_replaceMethod(nvc_class, push_sel, push_block, method_getTypeEncoding(push_method));
    });
    will_push = push;
}

定义一个设置函数（公开）

/**
 设置UINavigationController默认返回按钮内容

 @param image nil时为默认
 @param title nil时为默认
 */
void set_nvc_default_back(UIImage* image, NSString* title)
{
    static NSString* back_title;
    static PushBlock will_push = ^(UINavigationController* self, UIViewController* viewController, BOOL animated) {
        self.viewControllers.lastObject.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:back_title style:UIBarButtonItemStylePlain target:nil action:nil];
    };
    back_title = title;
    intercept_push(back_title?will_push:nil);
    [[UINavigationBar appearance] setBackIndicatorImage:image];
    [[UINavigationBar appearance] setBackIndicatorTransitionMaskImage:image];
}

下边是使用方式

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    set_nvc_default_back(nil, @"返回");
    
    return YES;
}

然后，既然做了全局处理，就想着是不是让这玩意能够让指定界面进行定制，用了个简单的办法，如下
定制一个协议

/**
 执行 set_nvc_default_back 后有效
 */
@protocol NavigationBackContentProtocol
-(NSString*)navigationBackItemTitle;
@end

然后修改 set_nvc_default_back 为

void set_nvc_default_back(UIImage* image, NSString* title)
{
    static NSString* back_title;
    static PushBlock will_push = ^(UINavigationController* self, UIViewController* viewController, BOOL animated) {
        NSString* title = back_title;
        if ([viewController conformsToProtocol:@protocol(NavigationBackContentProtocol)])
        {
            BCPViewController* vc = (BCPViewController*)viewController;
            title = [vc navigationBackItemTitle];
        }
        self.viewControllers.lastObject.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:title style:UIBarButtonItemStylePlain target:nil action:nil];
    };
    back_title = title;
    intercept_push(will_push);
    [[UINavigationBar appearance] setBackIndicatorImage:image];
    [[UINavigationBar appearance] setBackIndicatorTransitionMaskImage:image];
}

补充：BCPViewController 是个类型

typedef UIViewController<NavigationBackContentProtocol> BCPViewController;