UI基础 获取当前屏幕显示的viewcontroller

 #pragma mark - 获取当前屏幕显示的viewcontroller
 - (UIViewController *)getCurrentVC
 {
     UIViewController *result = nil;

     UIWindow * window = [[UIApplication sharedApplication] keyWindow];
     if (window.windowLevel != UIWindowLevelNormal)
     {
         NSArray *windows = [[UIApplication sharedApplication] windows];
         for(UIWindow * tmpWin in windows)
         {
             if (tmpWin.windowLevel == UIWindowLevelNormal)
             {
                 window = tmpWin;
                 break;
             }
         }
     }

     UIView *frontView = [[window subviews] objectAtIndex:];
     id nextResponder = [frontView nextResponder];

     if ([nextResponder isKindOfClass:[UIViewController class]])
         result = nextResponder;
     else
         result = window.rootViewController;

     return result;
 }

如果想进行push和pop，需要将调用方法得到的返回值强制类型转换为UINavigationController类型

 UINavigationController *NC = (UINavigationController *)[self getCurrentVC];
 [NC popViewControllerAnimated:YES];