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

[Josh Freeman]

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.)


> 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).

   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];

Cheers,

Josh