How to use NSInvocation to call a class method?

Question

I've a class method which is not declared in the h file, but implemented in the m file. now I want to call it in another class, since the return value is a int, I can't use selector directly, so I use NSInvocation.

below is what i'm doing:

SEL selector = ***;
NSMethodSignature *signature = [classA methodSignatureForSelector:selector];
NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:signature];
invocation.selector = selector;
invocation.target = [classA class];
[invocation setArgument:(void *)arg atIndex:2];
[invocation invoke];

the invoke doesn't succeed, Why?

if you want to call it in another than shouldn't it be in the .h as well..? — Ankit Srivastava, May 14 '13 at 11:58
@AnkitSrivastava I'm doing a unit test, the method are not supposed to be called outside — Jerrylk, May 15 '13 at 02:08

score 3 · Accepted Answer · answered May 14 '13 at 12:13

3

When passing the arguments, you pass their address, not their value. Try the following:

[invocation setArgument:&arg
                atIndex:2];

See [NSInvocation setArgument:atIndex:] in the class reference.

answered May 14 '13 at 12:13

trojanfoe

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I tried but failed, in fact the argument is a (NSDate *), it is unnecessary to use the '&' – Jerrylk May 15 '13 at 02:10
@Jerrylk look at the example in the link I provided, that also passes an object and uses `&`. – trojanfoe May 15 '13 at 18:11

How to use NSInvocation to call a class method?

1 Answers1