[Laszlo-dev] Adding default style attribute values

[P T Withington]

The key issue is making inheritance work.

The _only_ way to have it work is to mimic the way default attributes  
work in the tag compiler.  They get compiled into an alist that gets  
merged with subclass lists.

The old way, where default values came in one list and constraints  
came in another, and styles in another, etc.  Never really worked.   
There were always bugs where a constraint overrode a style that was  
closer when it should have taken the default, etc.  Now, everything  
comes in one list, and there are special objects in the alist that  
become constraints or styles or databindings, but the inheritance is  
one uniform computation -- subclass values shadow superclass values as  
expected -- and you just run down the merged list and install the  
values (or bindings) that surface.

So, whatever we do in the kernel has to work with that model.  There's  
no easy way.  The tag compiler does a lot of work to build the  
attribute list from a tag spec.  We either have to do that all by hand  
in the LFC, or we'd need to invent some new syntax and implement that  
in the script compiler.  Or, as Henry has suggested (and you just  
reminded me), we could start allowing LZX into the LFC.  This might be  
the way to go in the long run, but will require some changes to our  
build system, and obviously, we can't allow just _any_ LZX in the LFC,  
it has to be carefully bootstrapped.  But you could imagine that  
LzView becomes something like LzViewInternal in the LFC, 99%  
implemented in Javascript, and then we write the actual <view> tag in  
LZX, with documentation and default values.  This would probably make  
our documentation system much simpler too, since it would not have to  
parse Javascript for documentation.  Seems like a nice long-term  
project for remodularization.

In the short term, here is a sketch of something you could flesh out  
that should give us most of what you want.  There is the issue of how  
we document this -- I think it means editing the documentation of each  
attribute that you want to bind by default to a CSS attribute.  This  
is the brute force way.  We might be able to come up with a better  
solution where we create a new subclass of LzConstraintExpr that just  
records the correspondence between an attribute name and the CSS  
property name and builds a closure at runtime to install the correct  
constraint.  I'll have to think about that a little more...

  /** @access private
    * @modifiers override
    */
@@ -1073,6 +1117,9 @@
   * The background color of the view.  Setting <code>bgcolor</code> to
   * <code>null</code> will make the view transparent.
   *
+ * The background color of the view is controlled by the CSS property
+ * <code>background-color</code>
+ *
   * May be set to any valid CSS color specification.  When read, will
   * be read as the equivalent numeric value.  To retrieve a CSS color
   * specification, use <code>this.presentAttribute('bgcolor',
@@ -1097,6 +1144,16 @@
    this.bgcolor = bgc;
    if (this.onbgcolor.ready) this.onbgcolor.sendEvent( bgc );
  };
+  /**
+   * Default CSS style binder
+   * @access private
+   */
+  function $lzc$style_bgcolor(ignore) {
+    #pragma "userFunctionName=$style{'background-color'}"
+    this.__LZstyleBindAttribute('bgcolor', 'background-color',  
'color');
+  }
+  // Install that as the default in the class attributes table
+  attributes.bgcolor = new LzConstraintExpr('$lzc$style_bgcolor');

  /** The horizontal offset of this view's upper left corner from the
    * upper left corner of its container.


On 2009-10-06, at 06:44, Max Carlson wrote:

> Thoughts?
> -- 
> Regards,
> Max Carlson
> OpenLaszlo.org
>
> From: Max Carlson <max at openlaszlo.org>
> Date: 3 October 2009 22:27:39.000 EDT
> To: P T Withington <ptw at laszlosystems.com>
> Cc: OpenLaszlo development list <laszlo-dev at openlaszlo.org>
> Subject: Adding default style attribute values (was Re: [Laszlo- 
> reviews] For Review: Change 20090924-maxcarlson-T Summary: Compile  
> style attribute for <attribute/>)
>
>
> I definitely think we should try assigning standard CSS style  
> properties.  That way, many $style declarations can go away.
>
> A few options come to mind:
>
> 1. A LzInheritedHash of default stylename -> attribute mappings
> 2. Separate class properties similar to setter names, e.g.  
> style_visible = 'display';
> 3. Somehow hacking them into the existing attributes LzInheritedHash
>
> Then LzNode would call __LZstyleBindAttribute() for matching  
> attribute names...
>
> I hate to create a parallel mechanism to that used by the compiler,  
> but I don't see a way around it.  All three of these should support  
> inheritance.
>
> While we're on the subject, should compiler/AttributeSpec.java be  
> updated to know about styles?