Calling properties/instance variables from strings in Objective-C

Question

Basically my view controller has 49 different instance variables of class CircleView (called circleView1, circleView2, ..., circleView49). The CircleView class is a simple subclass of UIImageView and basically returns a circle picture when initialized.

Here is what I am trying to do:

In my implementation for the view controller, I want to be able to select the instance variable using a string, for example let's say I generate a random integer i between 1 and 49, lets say it's 5. I would like to be able to build an NSString using something like [NSString stringWithFormat @"circleView%i",i]; and somehow reach the actual circleView5 instance variable. Is this possible?

P.S. I'm looking for something in the lines of NSClassFromString, but which applies to instance variables or objects.

RyanR · Accepted Answer · 2011-07-07 17:00:34Z

5

KVC is your friend. Assuming you have a string with the name of the circleView in it,

NSString *myCircle = [NSString stringWithFormat:@"circleView%i", i];

you access that property on the controller using KVC:

CircleView *theCircle = [self valueForKey:myCircle];

On a side note, you should consider redesigning the object heirarchary; this will be very difficult to maintain, and there are certainly better ways to do it (an array with the CircleView's accessed by index would be my first choice).

edited Jul 7, 2011 at 17:00

answered Jul 6, 2011 at 22:47

RyanR

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4 Comments

Kaan Dedeoglu Over a year ago

That makes a lot of sense, I had figured [self setValue: forKey:] already but this was what I needed!! thank you so much

bbum Over a year ago

Actually, it will work just fine with an ivar defined without a property or accessor methods. And, yes, this smells like a re-architecture is in order.

RyanR Over a year ago

@bbum Is that an intended use of KVC, accessing ivars directly? It seems like that would circumvent willAccessValue/didAccessValue plumbing.

bbum Over a year ago

I believe the willChange/didChange gunk is still fired.

cajunluke · Accepted Answer · 2011-07-07 00:39:40Z

3

Instead of having a pile of variables and trying to access them via a string, use an array (either a primitive C array or an NSArray: I'll demo with an NSMutableArray). Declare a NSMutableArray *circleViews; in your class like you did the circleViewN instances. In your initializer, instead of a bunch of circleViewN = [[CircleView alloc] init];, you'd have something like:

circleViews = [NSMutableArray arrayWithCapacity:50];

for(int i=0; i<50; i++)
    [circleViews addObject:[[[CircleView alloc] init] autorelease]];

Then you can access the desired circle with your random int i with [circleViews objectAtIndex:i];.

edited Jul 7, 2011 at 0:39

answered Jul 6, 2011 at 22:54

cajunluke

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3 Comments

bbum Over a year ago

This is a much better solution overall.

Aidan Steele Over a year ago

@CajunLuke: You're leaking memory here, You should be autoreleasing your CircleView objects when adding them to the array.

cajunluke Over a year ago

@Sedate True. I've been doing so much Java at work I forgot about that.

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