目标C和C中的循环进口问题Cocoa Touch [英] Circular import issues in Objective C & Cocoa Touch

问题描述

我在Cocoa Touch中有一个视图控制器，它检测设备何时旋转，并在其所具有的2个视图控制器的视图之间切换：横向和纵向。

要让 UIViewControllers 能够访问 FRRRotatingViewController ，方法与所有 UIViewControllers 可以访问它们所在的 UINavigationController 。

UIViewController 将具有 rotationViewController 属性的子类（ FRRViewController 。

我还修改了 FRRRotatingViewController ，所以它需要 FRRViewControllers FRRRotatingViewController.h

code>在 FRRViewController.h （反之亦然），我似乎进入一个循环导入问题。我不知道如何解决它。有任何建议吗？

以下是代码：

  // 
 // FRRViewController.h 
 
 #import< UIKit / UIKit.h> 
 #importFRRRotatingViewController.h
 
 @interface FRRViewController：UIViewController 
 
 @end 
 
 // 
 FRRRotatingViewController.h 
 
 #import< UIKit / UIKit.h> 
 #importFRRViewController.h
 
 @class FRRRotatingViewController; 
 
 
 @protocol FRRRotatingViewControllerDelegate 
 
  - （void）FRRRotatingViewControllerWillSwitchToLandscapeView：（FRRRotatingViewController *）sender; 
  - （void）FRRRotatingViewControllerWillSwitchToPortraitView：（FRRRotatingViewController *）sender; 
 
 @end 
 
 
 @interface FRRRotatingViewController：FRRViewController {
 //这是我得到的错误：找不到接口声明
 //'FRRViewController'，'FRRRotatingViewController'的超类;你是
 //意思是UIViewController吗？ 
} 
 
 @property（strong）UIViewController * landscapeViewController; 
 @property（strong）UIViewController * portraitViewController; 
 
 @property（unsafe_unretained）id< FRRRotatingViewControllerDelegate>代表; 
 
  - （FRRRotatingViewController *）initWithLandscapeViewController：（UIViewController *）landscape andPortraitViewController：（UIViewController *）portrait; 
  - （void）deviceDidRotate：（NSNotification *）aNotification; 
 
 @end 
  

解决方案

可以在大多数情况下在头部中使用类和协议的前向声明，以避免循环导入问题，除了继承的情况。在 FRRViewController.h 中，不能导入 FRRRotatingViewController.h ，您不能进行向前声明吗？

  @class FRRRotatingViewController; 
  

I have a view controller in Cocoa Touch that detects when the device rotates and switches between the views of the 2 view controllers it has: landscape and portrait.

I want the UIViewControllers in it to be able to access the FRRRotatingViewController, in a similar way as all UIViewControllers can access the UINavigationController they're in.

So I created a UIViewController subclass (FRRViewController) that will have a rotatingViewController property.

I also modified FRRRotatingViewController, so it takes FRRViewControllers instead of plain UIViewControllers.

Unfortunately, when I include FRRRotatingViewController.h in FRRViewController.h (and vice versa), I seem to get into a circular import issue. I don't know how to fix it. Any suggestions?

Here's the code:

//
//  FRRViewController.h

#import <UIKit/UIKit.h>
#import "FRRRotatingViewController.h"

@interface FRRViewController : UIViewController

@end

//
//  FRRRotatingViewController.h

#import <UIKit/UIKit.h>
#import "FRRViewController.h"

@class FRRRotatingViewController;


@protocol FRRRotatingViewControllerDelegate

-(void) FRRRotatingViewControllerWillSwitchToLandscapeView: (FRRRotatingViewController *) sender;
-(void) FRRRotatingViewControllerWillSwitchToPortraitView: (FRRRotatingViewController *) sender;

@end


@interface FRRRotatingViewController : FRRViewController {
    // This is where I get the error:Cannot find interface declaration for
    // 'FRRViewController', superclass of 'FRRRotatingViewController'; did you 
    // mean 'UIViewController'?
}

@property (strong) UIViewController *landscapeViewController;
@property (strong) UIViewController *portraitViewController;

@property (unsafe_unretained) id<FRRRotatingViewControllerDelegate> delegate;

-(FRRRotatingViewController *) initWithLandscapeViewController: (UIViewController *) landscape andPortraitViewController: (UIViewController *) portrait;
-(void) deviceDidRotate: (NSNotification *) aNotification;

@end

解决方案

You can use forward declarations for classes and protocols in headers in most situations to avoid circular import issues, except in the case of inheritance. In FRRViewController.h, instead of importing FRRRotatingViewController.h, can you not make a forward declaration?

@class FRRRotatingViewController;

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