Objective-C头文件不能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的iPad游戏，其中包含一个填充了不同类型的瓷砖的板。我创建了一个自定义类 Tile 作为tile的一般模板和 Tile 的几个子类，它们有不同的属性和方法。我还创建了一个类 Board ，其中包括使用特殊的坐标系统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.

由于某些原因，在 Board 类中，编译器似乎没有识别 Tile 作为对象类型，即使我已经在文件的顶部添加了 #importTile.h。

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.

这里是相关的代码（只是询问是否有你想看到的代码的其他部分）：

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 / p>

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

此代码甚至不会构建，以下错误表示：

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

预期'（'在'Tile'之前

Expected '(' before 'Tile'

如果我将类型从（Tile *）更改为（NSObject *） ，它修正了错误，这使我相信 Tile 不被识别为一种类型的对象。

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.

我已经通过Google和此网站搜索，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;很容易解决。

Dumb mistake; easy to fix.

正如你们都指出的问题是，两个头文件正在导入每个其他，这是不允许的现在，我已经解决了这个问题，通过移动#importBoard.h语句到Tile.m，因为它不是在头文件中需要的，后来，如果我决定使用Board.h文件中的Board我将使用正向引用（@class Board;），作为您建议的几个。

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一个经典问题。这里有一个圆圈：Tile.h正在导入Board.h，它导入Tile.h。这会混淆编译器 - 它陷入循环。

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.

您通过不将标头导入标头来解决此问题。但是，仍然需要让编译器知道 Tile 。在Board.h中，制作转发声明：

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.

这保证编译器有一个类 Tile 将在运行时存在;您可以在标题的其余部分引用该名称。在 Board 的实现中，导入Tile.h.这将让编译器看到与需要它们的 Tile 类相关联的方法和属性。

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 #importBoard.h移动到Tile.m。因为你不是指在Tile.h中的 Board 类，所以不需要提前声明。

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.

通常，最好只将类头文件导入到需要它们的实现文件中。框架头，因为它们永远不会导致你的代码循环，可以和 - 因为你需要引用其中声明的许多类 - 应该导入到你的头。

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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