Objective C & 中的循环导入问题可可触摸 [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，用于检测设备何时旋转并在它拥有的 2 个视图控制器的视图之间切换:横向和纵向.

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.

我希望其中的 UIViewControllers 能够访问 FRRRotatingViewController，就像所有 UIViewControllers 都可以访问 >UINavigationController 他们在.

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.

所以我创建了一个 UIViewController 子类 (FRRViewController)，它将有一个 rotatingViewController 属性.

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

我还修改了 FRRRotatingViewController，所以它需要 FRRViewControllers 而不是普通的 UIViewControllers.

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

不幸的是，当我在 FRRViewController.h 中包含 FRRRotatingViewController.h 时(反之亦然)，我似乎陷入了循环导入问题.我不知道如何修复它.有什么建议吗?

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?

代码如下:

//
//  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

推荐答案

在大多数情况下，您可以在头文件中使用类和协议的前向声明来避免循环导入问题，继承的情况除外.在FRRViewController.h中，不导入FRRRotatingViewController.h，可以不做前置声明吗?

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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