obj-c access property dynamically

Question

I know the string name of a property of an object. How would one go on about getting and setting that property using the string?

Answer 1

@synthesize propertyName automates the generation of getter and setter methods.

The compiler generates

• - (id)propertyName;
• - (void)setPropertyName;

If you have a selector as NSString, you can use performSelector:NSSelectorFromString.
e.g.:
[object performSelector:NSSelectorFromString(@"propertyName") ...]

Answer 2

While @weichsel is correct, there is a better way.

Use:

[anObject valueForKey: @"propertyName"];

and

[anObject setValue:value forKey:@"propertyName"];

Obviously, @"propertyName" can be an NSString that is dynamically composed at runtime.

This technique is called Key Value Coding and is fundamental to Cocoa.

Why this is better is because -valueForKey will do what is necessary to "box" whatever type the property returns into an object. Thus, if the property is of type int, it'll return an NSNumber instance containing the int.

This is much easier to deal with -- performSelector will only work for types that happen to fit into a pointer's worth of memory.

Note that there is also -setValue:forKey:.