编译错误 - iOS“预期”）“之前”问题

Question

以下代码有什么问题？ Xcode 4说两个方法声明用＆＃34;问题＆＃34;由于＆＃39;＆＃34;期待＆＃34;）＆＃34;而不能编译。之前＆＃34;问题＆＃34 ;;消息，如下面代码中的注释所示。问题类编译，此代码以前一直在工作。我对问题进行了一些更改，但是将它们退出来试图弄清楚这个编译时错误。

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

@interface AppState : NSObject {

    int chosenAnswer;
    int correctAnswers;
    int currentQuestionNumber;

    // this will contain the hash table of question objects
    NSMutableDictionary *questionHash;

}

@property (nonatomic) int chosenAnswer;
@property (nonatomic) int correctAnswers;
@property (nonatomic) int currentQuestionNumber;
@property (nonatomic, retain) NSDictionary *questionHash;

- (void)        printQuestions;
- (void)        printDescription;
- (void)        addQuestion: (Question *) question; // <==== error  
- (int)         numberOfQuestions;
- (void)        saveState; 
- (void)        resetState;
- (Question *)  currentQuestion; //  <=====   error


@end

这里的问题：

#import <Foundation/Foundation.h>

#import "AppState.h"

@interface Question : NSObject {

    NSString    *questionTxt;
    int         correctAnswer;
    int         number;

    // this will contain the hash table of questions_answer objects
    NSMutableDictionary *answerHash;

}


@property (nonatomic, retain)   NSString * questionTxt;
@property (nonatomic) int       correctAnswer;
@property (nonatomic) int       number;
@property (nonatomic, retain)   NSMutableDictionary *answerHash;


 -(void)                            addAnswer: (NSString *) answer;   
- (NSMutableArray *)                answerArray;
- (void)                printDescription; 
- (void)                printAnswers;
- (NSString *)          correctAnswerText;
- (Question *)                      currentQuestion;

@end

Answer 1

循环依赖？ AppState正在导入问题，而问题正在导入AppState。

转发声明其中一个以打破周期，例如在AppState @interface语句之前使用@class Question，就像这样

@class Question;

@interface AppState : NSObject {

    int chosenAnswer;
    int correctAnswers;
    int currentQuestionNumber;

   // this will contain the hash table of question objects
   NSMutableDictionary *questionHash;
}
...

相关问题：@class vs. #import

Answer 2

当您在问题中#import“AppState.h”时，您会产生循环依赖。 最好将#import“AppState.h”和#import“Question.h”移动到实现部分。在标题中留下

@class Question;

和

@class AppState;

在接口声明之前。