[Laszlo-user] Need to be able to override resource declarations in OpenLaszlo without warnings.

[Sarah Allen]

  I think this is an excellent proposal.  cc'ing laszlo-user to see if 
other folks developing in LZX have strong feelings about this ...



On Tue, Aug 28, 2007 at  3:12 PM, Bret Simister wrote:



Currently, in the OpenLaszlo platform, it was decided that declaring a 
resource twice within an LZX app

causes a server warning. This was intended to help developers just  in 
case they accidentally overrode a

resource that had already been  declared in another library.



<!-- the following code produces a warning, but still compiles -->

<canvas>

     <resource name="logo" src="logo.gif" />

     <resource name="logo" src="logo2.gif" />



  <!-- view appears with logo2.gif -->

     <view resource="logo" />

</canvas>




At this time, I would suggest that  the  platform remove these warnings 
and have

the last resource declaration override all other previous declarations.



Here is why...



OpenLaszlo now has a CSS implementation. It gives developers an elegant 
method

of skinning their applications. This works, currently,  by first 
declaring a resource



<resource  name="someimage_rsc"  src="somepath/someimage.jpg" />



and then referring to that resource in a CSS selector



view[name="someview"] {

resource: someimage_rsc;

}






If a developer builds a library ....



   myCustomLibrary      ( folder )

      library.lzx

      myresources.lzx ( contains many resource definitions including 
'lowerRightCorner_rsc' )

      mystyles.css    ( contains many selectors including one that 
references 'lowerRightCorner_rsc' )

      ...             ( other class and source image files )



where  library.lzx  includes both   myresources.lzx and mystyles.css



Then library can be used with a simple inclusion in the main app.



<canvas>



<include name="myCustomLibrary" />



<!-- instance of a class from myCustomLibrary -->

<mycustomclass />



</canvas>





Let's assume that " mycustomclass " contains a number of resources, and 
that you ( as a developer )

only want to change one of those resources . The simplest method to 
accomplish this would be ...



<canvas>



<include name="myCustomLibrary" />



<!-- override resource definition "lowerRightCorner_rsc" defined earlier 
in myresouces.lzx -->

<resource name="lowerRightCorner" 
src="my_new_path/my_lower_right_corner.jpg" />




<!-- instance of mycustomclass that will now display

          the new resource based on the unchanged css selector -->

<mycustomclass />



</canvas>



Currently, this code would cause a compiler warning. To avoid these 
warnings ( without changing OpenLaszlo ) the  resouces.lzx file(s) and 
possibly the  library .lzx would have to be edited.



If instead, we allow for resource overriding, then ...



1) the original CSS and  resource files will remain unchanged

2) The old resource for " lowerRightCorner"  would NOT be included in 
the app

3) There  would be clean separation between external libraries and the 
skinning of theses libraries  included in an application.









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