CODEWITHSUNDEEP
iphoneiosobjective-ccocoansmutablearray
sarfarazsajjad
sarfarazsajjad

Reputation: 1238

how to set a property of an object inside a NSArray

I have written a class which has a property, I want to add instances of this class into a mutable array and after that I want to set the num property of the instances. but I dont know the correct syntax. Please tell me the correct syntax or method to do this.

@interface ClassA : NSObject

@property int num;

-(void) method;
+(id) getClassAObj:(int)number;

@end
--------------------------------
#import "ClassA.h"

@implementation ClassA

@synthesize num;

-(void) method{
    NSLog(@"ClassA method Called");
}
+(id) getClassAObj:(int)number {

    ClassA *obj = [[ClassA alloc] init];
    obj.num = number;
    return obj;

}

@end
-----------------------

now in main I want to set the num property manually but I dont know what is the correct syntax

int main(int argc, const char * argv[])
{

    @autoreleasepool {

        // insert code here...
        NSLog(@"Hello, World!");

        NSMutableArray *array = [NSMutableArray arrayWithObjects:
                                [ClassA getClassAObj:9],
                                [ClassA getClassAObj:4], nil];
        NSLog(@"%i",[[array objectAtIndex:0] num]);
        NSLog(@"%i",[array[1] num]);
        //array[1].num = 3;              <--- Help needed here
        //[[array[1]]num 3];             <--- this is also not correct syntax

        NSLog(@"%i",[array[1] num]);

    }
    return 0;
}

I dont know If I am wrong with the syntax or may be it is not possible to set a property of an object inside an array

Upvotes: 1

Views: 1122

Answers (2)

Nikola Kirev
Nikola Kirev

Reputation: 3152

Here you go:

ClassA *anObject = array[<index>];
[anObject setNum:<yourNumber>];

You can also use the [<array> objectAtIndex:<index>] method, but the above is the newer way to do it.

Good Luck!

EDIT:

If you want to validate the object (so it will not crash, but it will also not work as expected) your code can look like this:

id anObject = array[<index>];
if ([anObject isKindOfClass:[NSClassFromString(@"ClassA")]]) {
    [(ClassA *)anObject setNum:<number>];
}

If you want to validade the exact message (the setter in this case), you should check if the object responds to this selector. This is useful when you have objects of different classes, but they all respond to the message. It would look like this:

id anObject = array[<index>];
if ([anObject respondsToSelector:@selector(setNum:)) {
    [anObject setNum:<number>];
}

Upvotes: 7

morningstar
morningstar

Reputation: 9132

array[1].num = 3;

This would work, however, the problem is, the compiler loses track of type information about an object if you put it in an array. The runtime still recognizes what kind of object it is. You just have to politely inform the compiler.

((ClassA *)(array[1])).num = 3;

Upvotes: 3

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