iOS 替换navigationController 的push方法，使页面无痕获取上页面的pageCode

给navigationControler 添加一个分类

@implementation UINavigationController (Track)

- (void)track_pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    if (self.viewControllers.count < 2) {
        return;
    }
    
    UIViewController *currentVC = self.viewControllers[self.viewControllers.count - 2];
    
    //vc不存在
    if (!currentVC || !viewController) {
#if DEBUG
        NSAssert(NO, @"currentVC or pushVC not exsit");
#endif
        return;
    }
    
    //vc不支持VVSnowplowTrackParams协议
    if (![currentVC conformsToProtocol:@protocol(VVSnowplowTrackParams)] ||
        ![viewController conformsToProtocol:@protocol(VVSnowplowTrackParams)]) {
        NSLog(@"not conform VVSnowplowTrackParams protocol. Current: %@, Push: %@.", currentVC, viewController);
        return;
    }
    
    //设置来源页面
    [(id <VVSnowplowTrackParams>)viewController setSpReferrer:[(id <VVSnowplowTrackParams>)currentVC spUri]];
}

交换push 方法

  (void)vv_swizzleMethod
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [UINavigationController class];
        SEL originSelector = @selector(pushViewController:animated:);
        SEL swizzledSelector = @selector(new_pushViewController:animated:);
        [NSObject exchangeInstanceMethod:class originalSel:originSelector swizzledSel:swizzledSelector];
    });
}

- (void)new_pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    [self new_pushViewController:viewController animated:animated];
    [self track_pushViewController:viewController animated:animated];
}

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