Objective C calling method dynamically with a string

Question

Im just wondering whether there is a way to call a method where i build the name of the method on the fly with a string.

e.g. I have a method called loaddata

-(void)loadData;

to call this i would normally call it like

[self loadData];

But i want to be able to call it dynamically with a string e.g.

NSString *methodName = [[NSString alloc] initWithString:@"loadData"];
[self methodName];

This is a stupid example but i hope you get my point. I am using it for databinding classes that I am setting up for my IPad application. Hard to explain but to get it to fire I need to work out how to call a method with a string.

Any ideas?

Thanks

The method I want to call is a function that returns an NSString. — IPadHackAndSlash, Dec 15 '10 at 05:23

score 109 · Accepted Answer · answered Dec 15 '10 at 05:12

109

You can try something like

SEL s = NSSelectorFromString(selectorName);
[anObject performSelector:s];

answered Dec 15 '10 at 05:12

shreyasva

13,126
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101

In this situation the method returns a value which is an NSString in one case. I get an error saying Lvalue required as left operand of assignment. This is my code: SEL s = NSSelectorFromString(@"getIDString"); [self text] = [boundEntity performSelector:s]; – IPadHackAndSlash Dec 15 '10 at 05:18
what is [self text],where you assign the value return getIDString. – Ishu Dec 15 '10 at 05:25
`[boundEntity performSelector:s]` returns a value of type that does not match the type of `[self text]`. I think you need to set @property for text and call `[self setText:[[boundEntity performSelector:s]]]`. – shreyasva Dec 15 '10 at 05:27
9

performSelector may cause a leak because selector is unknown! – malhal Nov 07 '13 at 22:24
1

http://stackoverflow.com/questions/7017281/performselector-may-cause-a-leak-because-its-selector-is-unknown/20058585#20058585 – SexyBeast Oct 08 '14 at 20:05

score 13 · Answer 2 · answered Dec 15 '10 at 05:16

You can use the objc_msgSend function. It takes two parameters, the receiver and the selector to send to it:

objc_msgSend(self, someSelector);

You'll need to turn your string into the appropriate selector using NSSelectorFromString:

NSString *message = [self getSomeSelectorName];
objc_msgSend(self, message);

The method also takes a variable number of arguments, so you can send messages with any number of arguments.

NSString *message = [self getSomeSelectorNameWithManyArguments];
objc_msgSend(self, message, arg1, arg2, arg3, arg4);

Objective C calling method dynamically with a string

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