之前寫過一個處理這個玩意兒的文章，主要是設置返回按鈕的文字和圖片，今天介紹一個新做法，幾個api自行谷歌，我就直接上代碼了

為了方便，定義兩個類型

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

定義一個攔截函數（私有）

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

 @param push block代碼塊
 */
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;
}

定義一個設置函數（公開）

/**
 設置UINavigationController默認返回按鈕內容

 @param image nil時為默認
 @param title nil時為默認
 */
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];
}

下邊是使用方式

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

然后，既然做了全局處理，就想著是不是讓這玩意能夠讓指定界面進行定制，用了個簡單的辦法，如下
定制一個協議

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

然后修改 set_nvc_default_back 為

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];
}

補充：BCPViewController 是個類型

typedef UIViewController<NavigationBackContentProtocol> BCPViewController;