使用Objective-C类别时如何导入另一个视图控制器头文件？

Question

When I want to transition from one view controller to another, I import the second view controller's header file into my first view controller's header file, by writing #import "SecondViewController.h" . However, since I already defined UIColor category in my first view controller, when I try to import the second view controller, I enter the following error: Duplicate interface definition class for SecondViewController .

Here's my FirstViewController.h :

#import 
#import "SecondViewController.h"

@interface FirstViewController : UIViewController

@end

@interface UIColor (ColorWithInt)
+ (UIColor *)colorWithR:(CGFloat)red G:(CGFloat)green B:(CGFloat)blue A:(CGFloat)alpha;
@end

I didn't meet any such errors so far when I develop this app, so it's definitely this category that is causing the issue here. So is it feasible to use category when I want to import another view controller class? Or are there any alternative ways to extend UIColor ? I just want to define a function that takes RGB as 0 ~ 255 integer, not 0 ~ 1 floating values that UIColor uses on default.

I use iOS 7 and Xcode 5.

Answer 1

您可能#import "SecondViewController.h"两次，只需检查FirstViewController.h/m文件（如果两者都这样做）。

Answer 2

I have a feeling you're using this

@interface 

instead of

@implementation

in your .m file.

Answer 3

Self Answer

I found out that the issue is not related to either FirstViewController or SecondViewController - let alone the category; it's because I imported almost all class' header file in AppDelegate.h in order to initialize the relationship among UITabBarController , UINavitationController , RootViewController , and Core Data and its lots of required properties. I didn't know that when I import a class in AppDelegate.h I cannot import the class at some other class's header file. Delete #import "FirstViewController.h"; and #import "SecondViewController.h;" in AppDelegate.h and I find my app being build properly now. Thanks to those who left comments in this post.