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?

score 10 · Accepted Answer · answered Jan 10 '12 at 22:37

10

This might work;

__unsafe_unretained NSString *one = @"Hello World";

answered Jan 10 '12 at 22:37

Abizern

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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... – Joshua Weinberg Jan 10 '12 at 22:53
1

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! – phatmann May 22 '14 at 20:39

score 5 · Answer 2 · edited May 23 '17 at 11:50

5

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.

edited May 23 '17 at 11:50

Community

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answered Aug 10 '12 at 17:57

Yoav

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NSInvocation and ARC (Automatic Reference Counting)

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