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Question

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

Answer 1

+1 A:

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];

echo 2010-02-09 03:55:10

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

Martin Cote 2010-02-09 03:59:02

Good point. I was going from memory. Still the general idea is there...

echo 2010-02-09 04:00:45

@ 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)

suse 2010-02-09 04:03:40

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 2010-02-09 04:10:45

hey.. when i changed to id, the error has gone, and even the control is going to the method when i double click on it, but y it is not printing NSLog(@"hello"); method which is in -(void)FunctioninClass method??

suse 2010-02-09 04:14:04

Hey plz reply.. could you make out wher the mistake is.. because there is no error also. then y is it not printing Hello??

suse 2010-02-09 04:24:05

can you post some code?

echo 2010-02-09 04:24:16

NSString *Class_Name = [subarray objectAtIndex:1]; **// i'll be getting the class name from array...........** id myclass = [[NSClassFromString(@"Class_Name")alloc]init]; [myclass FunctioninClass];

suse 2010-02-09 04:35:09

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

echo 2010-02-09 04:36:54

No .:(:(i have set the breakpoint.. but control is not going till there

suse 2010-02-09 04:41:32

Control in debugger is not at all getting into this line... [myclass FunctioninClass];

suse 2010-02-09 04:44:52

i've this in a for loop,which is many strings to instantiate.

suse 2010-02-09 04:54:24

hey.. i got to know tat myclass is nil.. but y is it nil. As per your answer to point 1, you said it returns class name right?

suse 2010-02-09 05:29:22

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

echo 2010-02-09 05:55:07

@echo:Should the name of string [@"MyClass"] be same as name of Class name? i.e in your code,........ @interface MyClass ...........id myclass = [[NSClassFromString(@"MyClass") alloc] init];

suse 2010-02-09 09:43:09

hey .. thanks a loooooots :)

suse 2010-02-09 12:14:57

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