Re: Basic info about outlets
Re: Basic info about outlets
- Subject: Re: Basic info about outlets
- From: Graham Cox <email@hidden>
- Date: Thu, 15 May 2008 21:53:19 +1000
Yep, you're basically correct, sounds right to me.
When the nib is loaded, <documentWindow> will point to ("refer to")
the window object.
someMethod is able to simply use the variable <documentWindow> because
that is an instance variable of the MyDocument object, and all methods
of MyDocument are able to use the object's ivars as if they were
locally declared. This is one of the main reasons that OOP is a useful
way to program.
so someMethod could then message the window itself, for example:
- (void) someMethod
{
// set a property:
[documentWindow setTitle:@"Arrooooggahh!!"];
// read a property:
NSRect wFrame = [documentWindow frame];
}
If you're asking *how* this works, the answer lies in the Obj-C
runtime. Basically all of an object's methods are implicitly passed a
pointer to the object itself (self) as a hidden parameter to the
function that the method is wrapping. The compiler thus generates code
that makes use of this implicit parameter, so the real code is really
doing the equivalent of:
void someMethod( NSDocument* self )
{
setTitle( self->documentWindow, @"string" );
}
underneath, it's all procedural ;-) (I'm simplifying, it's not
literally quite like this, Find out more here: file:///Developer/Documentation/DocSets/com.apple.ADC_Reference_Library.CoreReference.docset/Contents/Resources/Documents/documentation/Cocoa/Reference/ObjCRuntimeRef/index.html)
.
hth,
G.
On 15 May 2008, at 9:30 pm, John Love wrote:
I *think* I understand about outlets and actions .. but now I am not
so
sure.
Specifically, if I set (NSWindow *)documentWindow as an Outlet in my
main
nib and I declare in MyDocument.h file:
interface MyDocument:NSDocument {
IBOutlet NSWindow *documentWindow;
}
...
- (void) someMethod:documentWindow;
and in MyDocument.m file:
- (void) someMethod {
// some operation that accesses a property of documentWindow
}
Okay, documentWindow is typed as a outlet in the main nib and in the
interface,.h, file ... and I have control-dragged from the FileOwner
to the
title bar of the Window, selecting "documentWindow" as the Outlet.
But,
just exactly HOW does the actual documentWindow object get passed so
that
someMethod can look at one of its properties?
This question is oriented to "behind the scenes".
Thanks in advance>
John Love
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