Objective-C 头文件无法将自定义对象识别为类型 [英] Objective-C header file not recognizing custom object as a type

问题描述

我正在使用 cocos2d 为 iPad 开发一个游戏，该游戏涉及一个充满不同类型图块的板.我创建了一个名为 Tile 的自定义类作为磁贴的通用模板，以及一些具有不同属性和方法的 Tile 子类.我还创建了一个名为 Board 的类，除其他外，它使用特殊坐标系跟踪所有图块的位置.

I'm working on a game for iPad using cocos2d which involves a board filled with different types of tiles. I've created a custom class called Tile as a general template for tiles and a few subclasses of Tile which have different properties and methods. I've also created a class called Board which, among other things, keeps track of the locations of all the tiles using a special coordinate system.

出于某种原因，在 Board 类中，编译器似乎没有将 Tile 识别为一种对象，即使我已经添加了 #import "Tile.h" 在文件的顶部.

For some reason, in the Board class, the compiler doesn't seem to be recognizing Tile as a type of object, even though I've added #import "Tile.h" at the top of the file.

这是相关的代码(直接问有没有你想看的其他部分的代码):

Here's the relevant code (just ask if there's other parts of the code you want to see):

Tile.h

#import <Foundation/Foundation.h>
#import "cocos2d.h"
#import "Board.h"

@interface Tile : NSObject

-(void) updateNeighbors;

@property (nonatomic, retain) CCSprite* sprite;
@property (assign) CGPoint coords;
@property (assign) CGPoint positionInPoints;
@property (nonatomic, retain) NSMutableArray *neighbors;

@end

Board.h

#import <Foundation/Foundation.h>
#import "cocos2d.h"
#import "Tile.h"

@interface Board : NSObject

+(Board*)sharedBoard;

- (void) putTile: (Tile*) tile AtIndex: (CGPoint) index; //<-- error here!
- (void) replaceTileAtIndex: (CGPoint) index1 WithTileAtIndex: (CGPoint) index2;
- (Tile*) tileAtIndex: (CGPoint) index; //<-- error here!
- (void) populate;

@property (nonatomic, retain) NSMutableArray *tiles;
@property (nonatomic, retain) NSString *type;
@property (assign) CGPoint size;

@end

此代码甚至无法构建，并且在指示的地方出现以下错误:

This code will not even build and I'm getting the following error where indicated:

'Tile' 前应为 '('

Expected '(' before 'Tile'

如果我将类型从 (Tile*) 更改为 (NSObject*)，它会修复错误，这让我相信 Tile未被识别为对象类型.

If I change the type from (Tile*) to (NSObject*), it fixes the error, which leads me to believe that Tile is not being recognized as a type of object.

我通过 Google 和本网站进行了搜索，但无法弄清楚为什么会发生这种情况.

I've searched via Google and this site and cannot figure out why this is happening.

愚蠢的错误；易于修复.

Dumb mistake; easy to fix.

正如大家所指出的，问题是两个头文件相互导入，这是不允许的.现在，我通过将#import "Board.h" 语句移到 Tile.m 来解决这个问题，因为头文件中不需要它.稍后，如果我决定在 Tile.h 文件中使用 Board，我将使用前向引用 (@class Board;)，正如你们中的一些人所建议的那样.

As you all have pointed out the problem is that the two header files are importing each other, which is not allowed. For now, I've fixed the problem by moving the #import "Board.h" statement to Tile.m, since it isn't needed in the header file. Later on, if I decide to use Board in the Tile.h file I will use forward referencing (@class Board;), as a few of you suggested.

再次感谢！

推荐答案

这是标题导入标题的经典问题.你在这里有一个圆圈:Tile.h 正在导入 Board.h，它导入了 Tile.h.这让编译器感到困惑——它陷入了一个循环.

This is a classic problem with headers importing headers. You have a circle here: Tile.h is importing Board.h, which imports Tile.h. This confuses the compiler -- it gets stuck in a loop.

您可以通过不将标头导入标头来解决此问题.但是，您仍然需要让编译器知道 Tile.在 Board.h 中，创建一个 "前向声明"类:

You solve this by not importing headers into headers. You still need to let the compiler know about Tile, however. In Board.h, make a "forward declaration" of the class:

#import <Foundation/Foundation.h>
#import "cocos2d.h"

@class Tile;    // Dear compiler, 
                // Tile is a class that I will need to refer 
                // to in this file. Please consider it to be a 
                // type; I promise it'll be defined at runtime. 
                // Sincerely, stephenalexbrowne

@interface Board : NSObject
//etc.

这向编译器保证有一个名为Tile的类将在运行时存在；然后，您可以在标题的其余部分引用该名称.在您的 Board 实现中，您导入 Tile.h.这将使编译器在需要它们的地方看到与 Tile 类关联的方法和属性.

This assures the compiler that there is a class called Tile that will exist at runtime; you can then refer to that name in the remainder of your header. In your implementation for Board, you import Tile.h. That will let the compiler see the methods and properties associated with the Tile class where they are needed.

同样，将 #import "Board.h" 移动到 Tile.m.由于您不是在 Tile.h 中引用 Board 类，因此您无需进行前向声明.

Likewise, move the #import "Board.h" into Tile.m. Since you aren't referring to the Board class in Tile.h, you don't need to make a forward declaration.

一般来说，最好只将您的类头文件导入到需要它们的实现文件中.框架头文件，因为它们永远不会导致您的代码循环，因此可以并且——因为您需要引用其中声明的许多类——应该导入到您的头文件中.

In general, it is best to import your class headers only into the implementation files where they are needed. Framework headers, since they will never cause a cycle with your code, can and -- because you need to refer to many of the classes declared in them -- should be imported into your headers.

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