NSInvocation and ARC (Automatic Reference Counting)

Question

When trying to migrate my current code to ARC, I'm getting errors whenever I pass an NSString as an NSInvocation argument.

Example:

NSInvocation inv = ...;
NSString *one = @"Hello World!";
[inv setArgument:&one atIndex:2];

The error happens when I use the Refactor -> Convert to Objective-C ARC option from the Edit menu. The text is "NSInvocation's setArgument is not safe to be used with an object with ownership other than __unsafe_retained."

How would I get around this?

Glance

Answer 1

This might work;

__unsafe_unretained NSString *one = @"Hello World";

Mediatorial

This will work, but you have to be VERY careful with the memory handling on this. I would recommend not using NSInvocation anymore if you can avoid it... – Outlander

I am using OCMock, and it passes an NSInvocation object into its callback blocks. If you don't use __unsafe_unretained on all the parameters ARC gets very unhappy. So thanks for the tip, mysterious crashes gone! – Haiphong

Answer 2

As Joshua Weinberg commented, using NSInvocation is not recommended anymore. If you have up to two parameters you can use performSelector. For three parameters or more, you can use NSObject's -methodForSelector: as explained here.

Pastypat