查找当前控制器

//获取当前屏幕显示的viewcontroller
- (UIViewController *)getCurrentVC {
    UIViewController *result = nil;
    UIWindow * window = [[UIApplication sharedApplication] keyWindow];
    //默认windowLevel是UIWindowLevelNormal
    if (window.windowLevel != UIWindowLevelNormal) {
        NSArray *windows = [[UIApplication sharedApplication] windows];
        for(UIWindow * tmpWin in windows) {
            if (tmpWin.windowLevel == UIWindowLevelNormal) {
                window = tmpWin;
                break;
            }
        }
    }
    id nextResponder = nil;
    UIViewController *appRootVC = window.rootViewController;
    if (appRootVC.presentedViewController) {
        nextResponder = appRootVC.presentedViewController;
    } else {
        UIView *frontView = [[window subviews] objectAtIndex:0];
        nextResponder = [frontView nextResponder];
    }
    if ([nextResponder isKindOfClass:[UITabBarController class]]){
        UITabBarController *tabbar = (UITabBarController *)nextResponder;
        UINavigationController *nav = (UINavigationController *)tabbar.viewControllers[tabbar.selectedIndex];
        result = nav.childViewControllers.lastObject;
    } else if ([nextResponder isKindOfClass:[UINavigationController class]]){
        UIViewController *nav = (UIViewController *)nextResponder;
        result = nav.childViewControllers.lastObject;
    } else {
        result = nextResponder;
    }
    return result;
}