Re: Code error in Your First Mac App tutorial..
Re: Code error in Your First Mac App tutorial..
- Subject: Re: Code error in Your First Mac App tutorial..
- From: "Gary L. Wade" <email@hidden>
- Date: Thu, 29 Dec 2011 18:55:36 -0800
Because there is no instance variable named textField, but there is one named _textField.
The property declaration makes available calls [self textField] and [self setTextField:x] which are the same as self.textField in get (x = self.textField) and set (self.textField = x) operations, respectively, and are method calls. The synthesize makes available self->_textField which can be shortened to _textField within the class's instance methods; this is the actual storage, not a method. If you left off the explicit name within the synthesize call, or even the prepended underscore, you could make all these look the same although they would still behave as described.
--
Gary L. Wade (Sent from my iPad)
http://www.garywade.com/
On Dec 29, 2011, at 6:07 PM, Peter Teeson <email@hidden> wrote:
> Thanks for your reply Ken. But I still don't understand. See bottom post.
>
> On 2011-12-29, at 5:23 PM, Ken Thomases wrote:
>> On Dec 29, 2011, at 3:38 PM, Peter Teeson wrote:
>>> I'm familiarizing myself with Xcode 4.2.1 under Lion 10.7.2 so am doing the "Your First Mac App" tutorial.
>>> This code snippet from the tutorial is incorrect and causes an error in compilation.
>>> if (sender == textField) { senderName = @"textField"; }…….
>>> The error is "Use of undeclared identifier 'textField'; did you mean _textField?"
>>> The correct code is:
>>> if (sender == self.textField){senderName = @"textField"; }
>>> In fact if you refer to any of the synthesized iVars such as 'window' or 'slider'
>>> or indeed any that you care to make up for yourself (eg aardvark) the same issue occurs.
>>> I don't know if this is a scope, language or compiler issue.
>>> Why would one need to use self.textField?
>> This is just an issue with the tutorial. Those properties are @synthesized with an explicit instance variable name, which is different from the property name due to the underscore prefix:
>> @synthesize textField = _textField;
>> You don't necessarily have to refer to "self.textField". You could have changed that line to be:
>> if (sender == _textField){senderName = @"textField"; }
>> The problem with the original is that it referred to an identifier "textField" which didn't correspond to any declared variable. The instance variable is called "_textField". And property names are not accessible just as naked identifiers; they need to be accessed using Dot Syntax (or, of course, using the getter or setter names or Key-Value Coding).
>> It was good of you to give that feedback to the document maintainers.
>> Cheers,
>> Ken
>
> The declaration in the Interface .h file, generated by making the Outlet connection. is:
> @property (weak) IBOutlet NSTextField *textField;
> To me that @property statement gives the explicit name textField.
> The generated @synthesize statement in the Implementation file is the one that assigns _textField isn't it?
>
> I understand that I could have used _textField. In fact in my research I tried it and it worked.
> Similarly for the other iVars window/_window and mute/_mute.
> Doing the digging is what led to me conclude there is some general rule which I do not yet know.
>
> I understand there is a special meaning for vars beginning with under bar but I still have to refresh my memory on
> Obj-C 2.0.
>
> So I repeat my question; can someone please explain why I had to use self.textfield?
>
> Thanks…
>
> Peter
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