Question

我不知道为什么会出现此错误。我有以下课程：

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

@interface Question : NSObject {
    NSString* qId;
    NSString* qTitle;
    NSString* qNumber;  
    NSString* sectionId;
    NSString* qType;
    Answer* answer;
}

@property (nonatomic, retain) NSString* qId;
@property (nonatomic, retain) NSString* qTitle;
@property (nonatomic, retain) NSString* qNumber;
@property (nonatomic, retain) NSString* sectionId;
@property (nonatomic, retain) NSString* qType;
@property (nonatomic, retain) Answer* answer;

#import "Question.h"

@implementation Question
@synthesize qId, qTitle, qNumber, sectionId, qType, answer;

-(id)init
{
    if (self = [super init])
    {
        // Initialization code here
        answer = [[Answer alloc]init];
    }
    return self;
}

-(void) dealloc{
    [answer release];
    [super dealloc];
}

@end

我在以下类中有一个类型为Question的属性：

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

@interface TextInputQuestionViewController : UIViewController {
    Question *question;
    IBOutlet UILabel *questionTitle;
    IBOutlet UILabel *inputLabel;
    IBOutlet UITextField *inputAnswer;
}

@property (nonatomic, retain) UILabel *questionTitle;
@property (nonatomic, retain) UILabel *inputLabel;
@property (nonatomic, retain) Question *question;
@property (nonatomic, retain) UITextField *inputAnswer;

- (void) addButton:(id)sender isLast:(BOOL)last;
- (void) setQuestionId:(NSString*)quId withTitle:(NSString*)quTitle number:(NSString*)quNum section:(NSString*)sId questionType:(NSString*)qt;

@end

我在.m文件中合成Question* question。

在我的QuestionnaireVieController类中：

#import <UIKit/UIKit.h>
#import "JSONKit.h";
#import "dbConnector.h"
#import "SliderQuestionViewController.h";
#import "TextInputQuestionViewController.h";
#import "MainMenuProtocol.h";

@interface QuestionnaireViewController : UIViewController {
    NSDictionary* questions;
    NSMutableArray* questionArray;
    NSMutableArray* answerArray;
    dbConnector* db;
    NSInteger currQNum; 
    NSString* qaTitle;
    NSString* secId;
    id<MainMenuProtocol>delegate;
}

@property(nonatomic, retain) NSDictionary* questions;   
@property(nonatomic, retain) NSMutableArray* questionArray;
@property(nonatomic, retain) NSMutableArray* answerArray;
@property(nonatomic, retain) dbConnector* db;
@property(nonatomic) NSInteger currQNum;
@property(nonatomic, retain) NSString* qaTitle;
@property(nonatomic, retain) NSString* secId;
@property(nonatomic, retain) id <MainMenuProtocol> delegate;

-(void) setQuestions;
-(void) startQuestion:(NSInteger)index isLast:(BOOL)last;
-(void) loadQuestions;
-(void) initialise;
-(void) finishQuestionnaire:(id)sender;
-(void) switchViews:(id)sender;

@end

我在.m文件中使用以下方法用不同类型的viewcontroller填充questionArray：

//assigns JSON to question objects
-(void) setQuestions {
    questionArray = [[NSMutableArray alloc] init];
    for (NSDictionary *q in self.questions) {               
        /* Create Question object and populate it */

        id question;
        if([[q objectForKey:@"type"] isEqualToString:@"Slider"]){
            question = [[SliderQuestionViewController alloc]init];              
            //set min max values
        }else if([[q objectForKey:@"type"] isEqualToString:@"Option"]){

        }else if([[q objectForKey:@"type"] isEqualToString:@"TextInput"]){
            question = [[TextInputQuestionViewController alloc]init];                       
        }else if([[q objectForKey:@"type"] isEqualToString:@"ImagePicker"]){

        }else{
            //comments          
        }
        [questionArray addObject:question];
        [question setQuestionId:[q objectForKey:@"questionId"] withTitle:[q objectForKey:@"question"] number:[q objectForKey:@"questionNumber"] section:[q objectForKey:@"sectionId"] questionType: [q objectForKey:@"type"]];
        [question release];

    }
}

当我在上面的.m文件中执行以下操作时：

NSLog(@"%@", [questionArray objectAtIndex:0]);

我明白了：

<TextInputQuestionViewController: 0x6062e90>

当我尝试做的时候：

NSLog(@"%@", [questionArray objectAtIndex:0].question);

我收到错误：

request for member 'question' in something not a structure or union

为什么它不能访问问题变量？特别是当它实际记录我的控制器对象时。我在这里错过了一些东西......

Answer 1

你正陷入疯狂的点符号。切换到这个，我打赌它有效（或者至少你得到一个有用的错误）：

NSLog(@"%@", [[questionArray objectAtIndex:0] question]);

Dot-notation是ObjC2中的一个鼓舞人心的补充，编译器仍然不能总是想出来，特别是当你试图将消息传递给id时（如objectAtIndex: }返回）。编译器感到困惑，认为这是你用于struct的点而不是伪装的消息，并且保释。

修改

foo.bar = baz; => [foo setBar:baz]; foo.bar.baz => [[foo bar] baz];

这，顺便说一句，是实际的Objective-C。点符号只是一种草率的写作方式。特别重要的是要了解foo.bar=baz 完全“将邮件setBar:发送给foo。”它的默认行为是使用声明的setter语义分配属性，但这只是默认值。您可以覆盖setBar:来执行任何操作。您甚至可以将消息调度系统重新配置为不调用方法setBar:（这不是一个模糊的功能，它由Core Data和Core Animation使用）。 Objective-C是一种动态语言，不幸的是，点符号通过使它看起来像Java而变得混乱。

Answer 2

如果您只需要引用Question对象，那么您可以定义一个类QuestionViewController，例如包含Question对象，并在SliderQuestionViewController和TextInputQuestionViewController中继承此类，当您想要从数组中获取对象时，您可以将它向下转换为QuestionViewController类型的对象：

Question * q = ((QuestionViewController *)[questionArray objectAtIndex:0]).question;
q.id = qId;
NSLog(@"%@", q.qId);

或者您可以简单地写一下：

Question * q = (Question*)[[questionArray objectAtIndex:0] question];
q.id = qId;
NSLog(@"%@", q.qId);

Answer 3

您是否在视图控制器中包含了Question.h？

即。

#include "Question.h"

帮助iphone应用程序 - 类属性引用问题

3 个答案: