错误:在Objective C中之前的期望说明符 - 限定符列表？

Question

每当我构建以下代码时,我都会收到上面的错误.

//Controller.h
#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import "PolygonShape.h"
#import "PolygonView.h";

@interface Controller : NSObject
{
    IBOutlet UIButton *decreaseButton;
    IBOutlet UIButton *increaseButton;
    IBOutlet UILabel *numberOfSidesLabel;
    IBOutlet PolygonShape *shape;
    IBOutlet PolygonView *shapeView;
}
- (IBAction)decrease;
- (IBAction)increase;
- (void)awakeFromNib;
@end


//Controller.m
#import "Controller.h"


@implementation Controller
@end    

但是,当我替换import语句并改为使用前向类引用时,代码将编译.

//Controller.h

#import <UIKit/UIKit.h>
#import <Foundation/Foundation.h>
#import "PolygonShape.h"
@class PolygonView;

@interface Controller : NSObject
{
    IBOutlet UIButton *decreaseButton;
    IBOutlet UIButton *increaseButton;
    IBOutlet UILabel *numberOfSidesLabel;
    IBOutlet PolygonShape *shape;
    IBOutlet PolygonView *shapeView;
}
- (IBAction)decrease;
- (IBAction)increase;
- (void)awakeFromNib;
@end

//Controller.m
#import "Controller.h"
#import "PolygonView.h"

@implementation Controller
@end

谁能解释一下？

Answer 1

是的,我也有这个循环依赖的问题,我在彼此导入这两个类.我也不知道前进宣言是什么.我在维基百科上及时搜索了它,但描述得很糟糕.我发现这篇文章解释了它们是什么以及它们与周期性进口的关系.http://timburrell.net/blog/2008-11-23/effective-c-cyclical-dependencies/

注意:链接不断下降所以我只是PDF了.

Answer 2

我有一个简单的错误得到了这个错误......也许其他人也这样做了？

正确:

@interface ButtonDevice : NSObject 

{

    NSString *name;
    NSString *uri;
    NSString *icon;
}

    @property (nonatomic, retain) IBOutlet NSString *name;
    @property (nonatomic, retain) IBOutlet NSString *uri;
    @property (nonatomic, retain) IBOutlet NSString *icon;
@end

错误:

@interface ButtonDevice : NSObject 
{

    NSString *name;
    NSString *uri;
    NSString *icon;

    @property (nonatomic, retain) IBOutlet NSString *name;
    @property (nonatomic, retain) IBOutlet NSString *uri;
    @property (nonatomic, retain) IBOutlet NSString *icon;
}   
@end

Answer 3

只需遵循此规则即可避免此类问题:

如果对象仅由类的实现文件在内部使用,则在头文件中使用 forward声明并在实现文件中导入/ include.否则在标题中使用 import.