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

[Bertrand Dekoninck]

Le 14 déc. 18 à 07:09, Josh Freeman a écrit :

> Hi Bertrand,
>
> On Dec 13, 2018, at 3:55 PM, Bertrand Dekoninck wrote:
>
> > In InterfaceBuilder (not Gorm here but it should be the same), I've  
> > also connected the "performClick" action from the textField to the  
> > addButton, so that the createTask method is also called when I type  
> > on the "Enter" key of the keyboard after editing the textField.
> >
> > It works as expected, but I've got extra calls to createNewTask :  
> > when the textField has the focus, performClick is also sent when  
> > clicking on another widget or if I use the "tab" key to cycle into  
> > another widget.
> >
> > Is there a way to avoid these ?
>
>   You can set the textfield to only send its action when Enter's  
> pressed (instead of every time editing finishes): In Interface  
> Builder, select the textfield, then show the Inspector panel. Under  
> the Inspector's Attributes tab, switch the textfield's 'Send Action'  
> mode from "End editing" to "Enter only". (You can also do this  
> programmatically by sending the textfield's cell a  
> setSendsActionOnEndEditing:NO message.)

Thanks a lot !

> > 2) The second problem is a memory management problem : in the  
> > createNewTask, I create a NSString using alloc +init.
> >
> > If I release that string at the end of the method, I've got a  
> > segfault if I try to add more than two tasks in the tasklist
>
>   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).

I wasn't aware I didn't need to allocate first but only to pass the  
pointer of [textField stringValue] to my new string.

>   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:
>
>        NSString *string = [textField stringValue];

Obviously then...

Thanks a lot.

Bertrand