Question

I don’t have a clue why this error is showing. I have the following class:

#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

I have a property of type Question in the following class:

#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

I synthesize Question* question in the .m file.

In my QuestionnaireVieController class:

#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

I use the following method in the .m file to populate the questionArray with different types of viewcontroller:

//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];

    }
}

When I do the following in the above .m file:

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

I get:

<TextInputQuestionViewController: 0x6062e90>

When I try to do:

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

I get an error:

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

Why on earth can it not access the question variable? Especially when it actually logs my controller object. am I missing something here…

Answer 1

You’re running into the madness that is dot-notation. Switch it to this, and I bet it works (or at least you get a useful error):

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

Dot-notation is a slapped-on addition in ObjC2, and the compiler still can’t always figure it out, especially when you’re trying to pass a message to an id (like objectAtIndex: returns). The compiler gets confused, thinks this this is the dot you use for a struct rather than a message in disguise, and bails.

---

EDIT

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

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

This, btw, is actual Objective-C. Dot-notation is just a sloppy way of writing this. In particular, it’s important to understand that foo.bar=baz is exactly “send the message setBar: to foo.” The default behavior for that is to assign a property using the declared setter semantics, but that’s just the default. You can override setBar: to do anything. You can even reconfigure the message dispatch system to not call the method setBar: (this is not an obscure feature, it’s used by Core Data and Core Animation). Objective-C is a dynamic language, and unfortunately dot-notation tends to muddy this by making it look like Java.