Access Objective-C property dynamically using the name of the property

objective-c reflection key-value-coding declared-property
quano picture quano · Dec 28, 2009 · Viewed 7.7k times · Source

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

Answer

bbum picture bbum · Dec 28, 2009

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:.

Related questions

Objective-C class -> string like: [NSArray className] -> @"NSArray"

I am trying to get a string name of a class from the class object itself. // For instance [NSArray className]; // @"NSArray" I have found object_getClassName(id obj) but that requires an instance be passed to it, and in my …

Read More
Create objective-c class instance by name?

Is it possible to create an instance of a class by name? Something like: NSString* className = @"Car"; id* p = [Magic createClassByName:className]; [p turnOnEngine]; I don't know if this is possible in objective-c but seems like it would be,

Read More
Objective-C Introspection/Reflection

Is there a built in method, function, API, commonly accepted way, etc. to dump the contents of an instantiated object in Objective-C, specifically in Apple's Cocoa/Cocoa-Touch environment? I want to be able to do something like MyType *the_thing = [[…

Read More