iphone - 错误 : expected specifier-qualifier-list before. ..在 Objective C 中？

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 语句并提供前向类引用时，代码可以编译。

//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，我也遇到了循环依赖的问题，我在其中相互导入了两个类。我也不知道前向声明是什么。我立即在维基百科上搜索了它，但它的描述很差。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'd it .