From: Lyle Johnson <lyle@...>
Date: 2003-01-15T04:35:31+09:00
Subject: Re: [FxRuby] Question on FXDataTarget

Joey Gibson wrote:

> I'm using FOX via FxRuby and I'm trying to get FXDataTarget going. If I
> wrap a local variable in an FXDataTarget and then put a FXTextField around
> that, everything seems to work fine. IOW, this works
> 
> @fooDt = FXDataTarget.new(0)
> @foo_input = FXTextField.new(self, 5, @fooDt, FXDataTarget::ID_VALUE, ...)
> 
> and then in a button's method
> 
> @fooDt.value = 99
> 
> the result is that the text field get's updated like it should. But what if
> I have an object whose members I want to connect to text fields? IOW, I
> have this class
> 
> class Foo
> 	attr_accessor :bar
> end
> 
> @foo = Foo.new
> @fooDt = FXDataTarget.new(@foo.bar)
> @foo_input = FXTextField.new(self, 5, @fooDt, FXDataTarget::ID_VALUE, ...)
> 
> and then in a button's method
> 
> @foo.bar = 99
> 
> the textfield does not get updated, even though the attribute of the object
> has been updated. 
> 
> Am I doing something wrong here?

The only thing you're doing wrong is attributing more power to the 
FXDataTarget than it actually has ;)

An FXDataTarget is a special kind of object that acts as a wrapper 
around some other object (its value). As you've already discovered, you 
can get or set the value of this wrapped-up object via the 
FXDataTarget#value() and FXDataTarget#value=() accessor methods, e.g.

     fooDt = FXDataTarget.new(0)
     fooDt.value = 99
     theValue = fooDt.value

When a widget like FXTextField interacts with a data target, it 
(indirectly) uses these accessors to get and set the value of the data 
target.

But when you initialize a data target with some value, e.g.

     fooDt = FXDataTarget.new(@foo.bar)

it just sets the value of its wrapped-up object to the current value of 
@foo.bar. In other words, both @foo.bar and fooDt.value are now 
references to the same object. But -- and this is the important part -- 
there's no way for the data target to change which object @foo.bar 
points to.