Assigning values to class instance from json output

Question

I am working on a code to create an app where a set of questions and it's options and answer are being fetched by json parsing. I'm doing all this in the viewDidLoad method.

This is the code so far. The parsing code is working fine.

- (void)viewDidLoad {
[super viewDidLoad];
question *quest = [[question alloc] init];
//Parsing code

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:[NSURL URLWithString:@"http://***/****/fetch.php"]];
[request setHTTPMethod:@"POST"];
NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
[[session dataTaskWithRequest:request completionHandler:^(NSData *data , NSURLResponse *response , NSError *error){
    NSError *err = nil;
    id jsonData = [NSJSONSerialization JSONObjectWithData:data options:0 error:&err];
    if (err) {
        [self alertMessage:(@"%@", err)];
    }
    else {

//Unclear from here   


        NSLog(@"%@", jsonData[@"data"]);
        allData = jsonData[@"data"];
        NSLog(@"%lu",(unsigned long)allData.count);
        int count = allData.count;
        int i = 0;
        while (i < count){
            question *que;
            NSString *q,*a,*o1,*o2,*o3,*o4;
            a = [allData valueForKey:@"answer"];
            q = [allData valueForKey:@"question"];
            o1 = [allData valueForKey:@"option1"];
            o2 = [allData valueForKey:@"option2"];
            o3 = [allData valueForKey:@"option3"];
            o4 = [allData valueForKey:@"option4"];

            //NSLog(@"%@", [allData valueForKey:@"question"]);
            [que setValue:q forKey:@"question"];
            [que setValue:a forKey:@"answer"];
            [que setValue:o1 forKey:@"option1"];
            [que setValue:o2 forKey:@"option2"];
            [que setValue:o3 forKey:@"option3"];
            [que setValue:o4 forKey:@"option4"];
            i++;

            NSLog(@"%@",[que valueForKey:@"question"]);
        }

    }
}] resume];

}

Here's how the output of the NSLog(@"%@", jsonData[@"data"]); code looks like in the console.

{
        answer = sometext;
        id = 7;
        option1 = sometext;
        option2 = sometext;
        option3 = sometext;
        option4 = sometext;
        question = "sometext";
    },           
        {
        answer = sometext;
        id = 9;
        option1 = sometext;
        option2 = sometext;
        option3 = sometext;
        option4 = sometext;
        question = "sometext";
    }
)

As far as I understand this json data is an array of dictionary(?)

The next step I'm doing is I have created a "questions" class. I am not sure if I did it right but here's the code for that:

#import "question.h"
@implementation question {    
NSString *q;
NSString *a;
NSString *o1;
NSString *o2;
NSString *o3;
NSString *o4;       
}
@end

In the while loop in the viewDidLoad method i'm trying to create am instance of question class called que which I'm trying to populate as shown in the code. But the line NSLog(@"%@",[que valueForKey:@"question"]); gives null in the console.

I'm sure it has got to be something wrong with the method I'm using.

The second problem is that I'm creating an array of question called quest which I'm declaring right after viewDidLoad. But then I wouldn't be able to use it in any other code blocks like the click event of a button. If I try to use the question *quest = [[question alloc] init]; line above viewDidLoad it gives an error :

initialiser element is not a compile-time constant

I know that this is not the ideal way to code but I'm still a beginner here and am just confused with all these new concepts. I have developed the same app in Swift but Objective C feels too hard. Any help would be appreciated.

Rajat · Accepted Answer · 2016-10-24 05:37:17Z

To get what you wanted first of all you have to create an NSMutableArray which will store instance of Question Class, and you have to declare it as a Global Array like this

@interface MyClass ()  {
    NSMutableArray * arrQuestion;
}

Now, in question.h, you have to declare the @property for all the variables like this, also the question class will be derived from NSObject as you are creating it as a Model class

@interface question : NSObject
@property (nonatomic, strong) NSString *strQuestion;
@property (nonatomic, strong) NSString * strAnswer;
@property (nonatomic, strong) NSString * strOptionA;
@property (nonatomic, strong) NSString * strOptionB;
@property (nonatomic, strong) NSString * strOptionC;
@property (nonatomic, strong) NSString * strOptionD;  
@end

Now in the while loop you have to create new instance of your Question class and have to assign the value in it like this

arrQuestion = [NSMutableArray new];
while (i < count){
      question *quest = [[question alloc] init];
      quest.strQuestion = [[[jsonData objectForKey:@"data"]objectAtIndex:i] objectForKey:@"question"];
      quest.strAnswer = [[[jsonData objectForKey:@"data"]objectAtIndex:i] objectForKey:@"answer"];
      quest.strOptionA = [[[jsonData objectForKey:@"data"]objectAtIndex:i] objectForKey:@"option1"];
      quest.strOptionB = [[[jsonData objectForKey:@"data"]objectAtIndex:i] objectForKey:@"option2"];
      quest.strOptionC = [[[jsonData objectForKey:@"data"]objectAtIndex:i] objectForKey:@"option3"];
      quest.strOptionD = [[[jsonData objectForKey:@"data"]objectAtIndex:i] objectForKey:@"option4"];
      i++;
      [arrQuestion addObject:quest];
}

Now from arrQuestion you can access the values like this

question *quest = [arrQuestion objectAtIndex:0]; //For Example value at 0 index
NSLog(@"Value of first question - %@", quest. strQuestion);

Thank you!. This worked. Now I know what I was doing wrong.! Thanks again for the help!

john elemans · Accepted Answer · 2016-10-24 05:37:29Z

1

quest is not declared as an array. Declare the array in your class definition (in your .h file). eg -

  NSMutableArray *questionsArray;

Make sure that you initialize it before you start trying to add data in the data parsing (you should move the parsing into its own method, too, not in the viewDidLoad method);

 questionsArray = [[NSMutableArray alloc] initWithCapacity:20];

You can use key/value properties but something like;

  que.answer = [allData valueForKey:@"question"];

is cleaner (imo). After a question is parsed, you can add it to your array like this;

  [questionsArray addObject:que];

edited Oct 24, 2016 at 5:37

answered Oct 24, 2016 at 5:29

john elemans

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1 Comment

Ajil O. Over a year ago

Thanks for the tip! I've moved the the parse section to a method of it's own.

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