这是循环引用吗？

Question

我有一个继承自 CCSprite 的类，名为 GameObject。我还有一个名为 ActionDispatcher 的单例，它继承自 NSObject。

ActionDispatcher sharedActionDispatcher 的工作是在请求时返回一个 CCActionInterval，而执行此操作的方法需要引用请求对象，该对象的类型为 GameObject（或其子类）。但要让 GameObject 能够请求此操作，它需要引用 ActionDispatcher。所以我在 ActionDispatcher 标头中有一个 #import "GameObject.h" ，在 GameObject< 中有一个 #import "ActionDispatcher" /代码> 标头。

我收到错误：在引用 GameObject 的 ActionManager 方法中，Expected ')' before 'GameObject'。

编辑：添加评论以显示我根据下面接受的答案修复此问题的位置。

---

//The GameObject interface

#import "cocos2d.h"
#import "ActionDispatcher.h"

@interface GameObject : CCSprite {
    CGPoint homeLocation;
}

@property (readwrite) CGPoint homeLocation;

- (void)updateStateWithDeltaTime:(ccTime)deltaTime 
        andListOfGameObjects:(CCArray*)listOfGameObjects;

@end

---

//The GameObject implementation

#import "GameObject.h"

@implementation GameObject

@synthesize homeLocation;

- (void)updateStateWithDeltaTime:(ccTime)deltaTime 
        andListOfGameObjects:(CCArray *)listOfGameObjects 
{
    //CCLOG(@"updateStateWithDeltaTime method should be overriden");
}

@end

---

//The ActionDispatcher interface

#import "cocos2d.h"
#import "CCRotateAround.h"
#import "Constants.h"
#import "GameObject.h" // Answer: Remove this line

// Add this here: @class GameObject;

@interface ActionDispatcher : NSObject {

}

+ (ActionDispatcher *)sharedActionDispatcher;

- (id)actionWithType:(ActionType)actionType 
          withObject:(GameObject *)gameObject 
        withDuration:(float)duration;

@end

---

//The ActionDispatcher implementation

#import "ActionDispatcher.h"
// and add this here: #import "GameObject.h"

@implementation ActionDispatcher

static ActionDispatcher* _sharedActionDispatcher = nil;

+ (ActionDispatcher*)sharedActionDispatcher 
{
    @synchronized([ActionDispatcher class])                             
    {
        if(!_sharedActionDispatcher)                                    
            [[self alloc] init]; 
        return _sharedActionDispatcher;                                 
    }
    return nil; 
}

+ (id)alloc 
{
    @synchronized ([ActionDispatcher class])                            
    {
        NSAssert(_sharedActionDispatcher == nil,
                 @"Attempted to allocated a second instance of the ActionManager singleton");                                          
        _sharedActionDispatcher = [super alloc];
        return _sharedActionDispatcher;                                 
    }
    return nil;  
}

- (id)actionWithType:(ActionType)actionType 
          withObject:(GameObject *)gameObject 
        withDuration:(float)duration
{
    CGSize screenSize = [[CCDirector sharedDirector] winSize];

    id action = nil;

    switch (actionType) {
        case kActionDiveBomb:
            CCLOG(@"ActionManager returning action of type: dive bomb");
            CGPoint controlPoint1 = ccp(gameObject.position.x, gameObject.position.y*0.5f);
            CGPoint controlPoint2 = ccp(screenSize.width*0.5f, gameObject.position.y*0.5f);
            CGPoint destination = ccp(screenSize.width*0.5f, -gameObject.contentSize.height*0.5f);
            ccBezierConfig diveBombBezier;
            diveBombBezier.controlPoint_1 = controlPoint1;
            diveBombBezier.controlPoint_2 = controlPoint2;
            diveBombBezier.endPosition = destination;
            id diveAction = [CCBezierTo actionWithDuration:duration bezier:diveBombBezier];
            id returnToTopAction = [CCMoveTo actionWithDuration:0.0f position:ccp(gameObject.homeLocation.x, screenSize.height+gameObject.contentSize.height/2)];
            id fallInAction = [CCMoveTo actionWithDuration:duration*0.2 position:gameObject.homeLocation];
            action = [CCSequence actions:diveAction, returnToTopAction, fallInAction, nil];
            break;
        case kActionLoop:
            CCLOG(@"ActionManager returning action of type: loop");
            CGPoint centerPoint = ccp(screenSize.width/2, screenSize.height/2);
            float span = 360.0;
            action = [CCRotateAround actionWithDuration:duration centerPoint:centerPoint spanAngle:span];
            break;
        case kActionSpin:
            CCLOG(@"ActionManager returning action of type: spin");
            action = [CCRotateBy actionWithDuration:duration angle:360.0f];
            break;
        case kActionGoHome:
            CCLOG(@"ActionManager returning action of type: go home");
            action = [CCMoveTo actionWithDuration:0.0f position:[gameObject homeLocation]];
            break;
        case kActionFallIn:
            CCLOG(@"ActionManager returning action of type: fall in");
            action = [CCMoveTo actionWithDuration:duration position:[gameObject homeLocation]];
            break;
        case kActionIdle:
            CCLOG(@"ActionManager returning action of type: idle");
            action = [CCDelayTime actionWithDuration:duration];
            break;
        default:
            CCLOG(@"ActionManager returning action of type: no valid action");
            break;
    }

    return action;
}

@end

Answer 1

只需在 ActionDispatcher.h 中的 @interface 上方添加一个 @class 指令即可。这是在实现中导入的类的前向声明。

@class GameObject;

Answer 2

可能的。尝试

@class GameObject

在 ActionManager.m 中导入后插入前向声明？这应该会打破这个循环。

Answer 3

这不是问题。 #import 指令自动处理已包含文件的包含。 讨论在这里。
要检查它是否注释掉所有其他导入，请从 NSObject 子类化您的 GameObject，它将编译而不会出现错误。
该错误表明您包含的文件之一存在问题。有时，它可能是头文件中 @end 关键字后面的错误符号，这会使编译器在错误的位置发出错误消息。