Question

I’m playing around with Julius Guzy’s sample code for creating a document based application that can save text files. I ran his code and it works perfectly and the app runs/save files (All in the latest version of Xcode. Though Guzy’s sample code compiles using the 10.6 SDK). I’m trying to learn from it and rewrite the code. I have everything in order to compile the app but for the strangest thing in MyDocument.m. I am unable to run it.

@synthesize nsTextViewObj;

Xcode is giving me this error, which I don’t really understand it.

Existing ivar ‘nsTextViewObj’ for property ‘nsTextViewObj’ with
assign attribute must be __unsafe_unretained

nsTextViewObj; is suppose to be linked to the “File Owners” in IB. I did that in the first place. It beats me why I’m getting that error. SDK conflicts maybe? How can I fix this?

Answer 1

ARC requires some changes to the code. Xcode provides a tool to automatically convert non-ARC code to ARC: Edit / Refactor / Convert to Objective-C ARC…

The Xcode tool is a good start, still I would recommend you to read Transitioning to ARC Release Notes.

I don’t know Julius Guzy’s code, but probably you should change it to something like:

@interface ifc_name : NSWindowController {
    NSTextView *__unsafe_unretained nsTextViewObject;
}
@property (unsafe_unretained) NSTextView *nsTextViewObject;

As the name implies, unsafe_unretained is not safe: when the object is deallocated, your reference is invalid. If you are deploying only to iOS 5 or higher, and OS-X 10.7 or higher, you can use weak instead. With weak your reference will become zero when the object is deallocated.