Hi,
> ... But when the complexity of the actions increases, I
> will attempt to consolidate logic in member functions which are called
> from
> the listeners...
You can do that without making them member functions, if you like. There's
no reason you can't have named functions inside your constructor or your
__initLayout method. Those named functions will have access to the
variables (and parameters) of the function they're inside, even after that
function terminates -- an idea which is probably a bit alien if (like me)
you're from a C or Java background.
E.g.:
=================================
someSetupMethod : function()
{
var textfield;
var checkbox;
// Create text field
textfield = new qx.ui.form.TextField;
// (add to doc, etc.)
// Create checkbox
checkbox = new qx.ui.form.CheckBox("Enable text field");
checkbox.setChecked(true);
// (add to doc, etc.)
// Have checkbox toggle text field's "enabled" state via
handleChangeChecked
checkbox.addEventListener("changeChecked", handleChangeChecked);
// The handleChangeChecked function
function handleChangeValue()
{
// Enable the text field if checked (by inheriting), disable it if
unchecked
textfield.setEnabled(this.getChecked() ? "inherit" : false);
}; // <== You want this semicolon: Declaring a function is a statement,
// statements need terminators, don't trust JS's "terminator
insertion"
},
=================================
The handleChangeValue method's scope inherits the textfield (and checkbox)
variables from someSetupMethod's scope, and keeps them after someSetupMethod
terminates -- because they haven't gone out of scope. (This doesn't just
happen with named functions, it happens with the anonymous ones you're
already using, too, whether they reference the variable(s) or not. You can
see how it's pretty easy to set up memory leaks in JavaScript if you're
unwary.)
Now, in the above, both the text field and the event handler for the
checkbox are private -- no one can get at them from the outside. But in
your original post, you wanted a public method that would access a private
variable (the text field). You can do that, too:
=================================
someSetupMethod : function()
{
var textfield;
// Create text field
textfield = new qx.ui.form.TextField;
// (add to doc, etc.)
// Create a public method to return the value
this.getTextValue = function() {
return textfield.getValue();
};
},
=================================
Now, users of your class can call getTextValue -- it's public -- but the
textfield reference is private. At first this seems to conflict a bit with
Qooxdoo's class declaration mechanism, because you're defining the public
method inside a method rather than as a member in the data structure you
pass into qx.Class.define. I don't think it's a problem, though I haven't
tried it yet (too new to Qooxdoo). You could just define an empty method
for qx.Class.define -- for instance, so you get to use Qooxdoo's excellent
documentation automation -- and then you're just refining (okay, replacing)
it later in someSetupMethod. E.g.:
=================================
someSetupMethod : function()
{
var textfield;
// Create text field
textfield = new qx.ui.form.TextField;
// (add to doc, etc.)
// Create a public method to return the value
this.getTextValue = function() {
return textfield.getValue();
};
},
getTextValue: function()
{
// The implementation of this is defined in someSetupMethod
},
=================================
I'd expect that to work because someSetupMethod will be called after
qx.Class.define processes the data structure with the placeholder.
If you have lots of temporary variables you use in your setup method, you'll
want to be aware that they're preserved by any named or anonymous function
you define in the setup method, whether they're referenced by those
functions or not (because JavaScript is a dynamic language). There are
syntactic ways around this, allowing you to only preserve the ones you want
preserved.
If you want to get into the depths of JavaScript's rather interesting (and
powerful, and frightenting) scoping features, check out
http://www.crockford.com.
FWIW
--
T.J. Crowder
tj at crowder software dot com
----- Original Message -----
From: "mshillin" <[EMAIL PROTECTED]>
To: <qooxdoo-devel@lists.sourceforge.net>
Sent: Wednesday, October 03, 2007 2:16 PM
Subject: Re: [qooxdoo-devel] Use of "this" to access class member
variables/UI components
>
> It is not a problem to code like this - I just wanted to make sure I am
> coding the correct way and there was not some "trick" to accessing UI
> components in a layout. It is a bit of a hassle when I am refactoring.
>
> If I perform "simple actions" on UI components, the logic goes into event
> listeners that are defined in-line. I don't make the UI components
> members,
> because I don't have to. But when the complexity of the actions increases,
> I
> will attempt to consolidate logic in member functions which are called
> from
> the listeners. When I do this, I have to go back and make the UI
> components
> class members so the member functions can "see" them. This means
> pre-pending every UI component reference with "this."
>
> Maybe I am just used to programming in Java and not Javascript.
>
>
>
> --
> View this message in context:
> http://www.nabble.com/Use-of-%22this%22-to-access-class-member-variables-UI-components-tf4561133.html#a13018774
> Sent from the qooxdoo-devel mailing list archive at Nabble.com.
>
>
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