Re: Need advice about NSTextField, performClick IBAction, and memory management

[David Chisnall]

On 14/12/2018 06:09, Josh Freeman wrote:
>     These three lines in createNewTask: cause the issue:
>
>          NSString *string = [[NSString alloc] init];
>          string = [textField stringValue];
>      ...
>      [string release];// With this, I've got an "exec_BAD_ACCESS" error 
> when calling three times in a row createNewTask with the same string in 
> textField
>
>
>     The first line sets 'string' to a retained, empty string object. The 
> next line sets 'string' to the object returned by [textField 
> stringValue], leaking the previous string object (its address was 
> forgotten while it was still retained). 'String' then points to an 
> object that wasn't retained by your code, so sending it a release 
> message will cause it to deallocate while it's still referenced 
> elsewhere (segfaulting if it's accessed after that).
>
>     You can fix the issue by removing the first & third lines 
> (empty-string allocation, release call), and moving the 'string' var 
> definition to the second line:

Note: you can also fix the issue by removing all references to retain / 
release and compiling with -fobjc-arc.  There is absolutely no reason 
for not doing this in new Objective-C code.  It will work with macOS, 
iOS, watchOS, tvOS, and GNUstep, and the compiler will generate code 
that is faster, smaller, and more likely to be correct than if you do 
this by hand.

David