获取当前的 viewController

- (UIViewController *)currentController {
    UIViewController *result = nil;
    UIWindow *window = [[UIApplication sharedApplication] keyWindow];
    
    if (window.windowLevel != UIWindowLevelNormal) {
        NSArray *windows = [[UIApplication sharedApplication] windows];
        
        for (UIWindow *temWin in windows) {
            if (temWin.windowLevel == UIWindowLevelNormal) {
                window = temWin;
                break;
            }
        }
    }
    
    UIView *frontView = [[window subviews] objectAtIndex:0];
    id nestResponder = [frontView nextResponder];
    if ([nestResponder isKindOfClass:[UIViewController class]]) {
        result = nestResponder;
    } else {
        result = window.rootViewController;
    }
    return result;
}