how to instantiate an object of class from string in Objective-C?

Question

I've a String who's value is the name of the Class[MyClass] which has to be instantiated, and MyClass has a method called

 -(void)FunctionInClass;

i'm using the method called NSClassFromString to instantiate MyClass.I want to know

1) what does NSClassFromString return?? 
2) what is id? 
3) How to call method -(void)FunctioninClass which is in MyClass using the instance.

how should i proceed , i'm doing it in Objective-C for iPhone app?

echo · Accepted Answer · 2010-02-09 04:09:53Z

59

1) what does NSClassFromString return??

It returns a Class, which means you can do [[NSClassFromString(@"MyClass") alloc] init]; see Mac Dev Center Docs for more info.

2) what is id?

See http://www.otierney.net/objective-c.html#idtype

3) How to call method -(void)FunctioninClass which is in MyClass using the instance.

id myclass = [[NSClassFromString(@"MyClass") alloc] init];
[myclass FunctioninClass];

edited Feb 9, 2010 at 4:09

answered Feb 9, 2010 at 3:55

echo

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13 Comments

Martin Cote Over a year ago

AFAICT, NSClassFromString is a function, not a class. Point 1 would become NSClassFromString( @"MyClass" )

suse Over a year ago

@ point 1) if NSClassFromString is returning a class, then that class has to be instantiated n then we can call FunctioninClass method right? but @ point 3) we are directly using the class named myclass and calling function. I tried with point 3) its giving me an error: MyClass undeclared(first use in function) and myclass undeclare (first use in function)

echo Over a year ago

Try it like this: id myclass = [[NSClassFromString(@"MyClass") alloc] init]; If the calling code does not know what MyClass is, you'll get the error you described. By using id as the variable type, you avoid this.

echo Over a year ago

if you set a breakpoint in FunctioninClass, does the breakpoint get hit?

echo Over a year ago

Here's a simple cocoa app that seems to do what you're looking for. I created a new Xcode project called "Untitled". pastee.org/ps83z

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Motti Shneor · Accepted Answer · 2019-03-12 10:09:55Z

0

NSClassFromString() is a function that returns an Objective-C class. That is, in Objective-C a class is an honourable object. An instance of the "Class" class...

And what is an Objective-C class good for?

for instantiating objects (via alloc init ) for introspection and reflection - to query it for the methods and properties instances of that class are exposed to the user for archiving/de-archiving instances of that class, and... to be able to run class methods (methods that do not require any specific instance of that class.

your last lines actually create an instance of the class whose name is the string passed to NSClassFromString.

answered Mar 12, 2019 at 10:09

Motti Shneor

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