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 <p.tee...@bell.net> 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 _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
