[litwindow-users] Implementing generic UI patterns (was Re: add/modify/delete pattern)

[Hajo K. <mai...@ha...>]

Hi Jake,

(this is a cross post from gmane.comp.lib.litwindow.user that hopefully 
is also of interest to the current GUI discussion on the boost list. The 
question was how to write a generic implementation for the 
add/modify/delete user interface pattern)

Jake Skinner wrote:
> I am having some difficulty getting my head around the RULE syntax and
> what can be achieved. I am trying to implement the add/modify/delete
> pattern which appears to have been catered for.
> 

you are a bit ahead of the litwindow schedule here.

I've put up a new article on the website (a correction of the few layout 
problems will appear later this day)

http://www.litwindow.com/Library/Articles/rapidui_article_3.htm

Here is what works:

You can already handle the 'modify' part of the add/modify/delete 
pattern. Have a look at the RSS Reader tutorial, Step 3 and 4 in the 
documentation.

Here is what does not yet work:

Action rules have yet to be defined. So you cannot fire an action using 
the rules and that is the reason why the add/modify/delete rule has to 
be written yet.

To implement Add you will have to intercept the event yourself.

What you can do is write a generic algorithm to add a new element and 
show it. Here is the rough outline:

void AddElement(RapidUI &r, string listBoxName)
{
     // first get the aggregate object for the list box
   aggregate listbox=r.GetWindowAccessor(listBoxName).get_aggregate();
     // next get a container object for the "Items" property
     // of the list box
   container items=listbox["Items"];
   if (items.is_valid()==false) {
     lw_log() << "Cannot add! List box is not attached to a container.";
     return;
   }
     // now get an accessor to the currently selected element
   accessor element=listbox["Current"];
     // this accessor will contain valid *type* information
     // even if no *current* element is selected

     // the next line will create a new object on the heap with 'new'
     // the new object will have the same type as 'Current'
   accessor newObject=create_object(element.get_type());

     // insert it (copying it) at the first position into the container
   items.insert(items.begin(), newObject);
     // delete the temporary object since a copy of it is now contained
     // in the container
   newObject.destroy();

     // finally tell RapidUI to update the UI
     // this will update the list box and the new element will
     // be shown at position 1
   r.ValueChanged(items.get_accessor(), false, false);
}

This is a generic function, meaning that it will work
- with any kind of container
- with any type of elements contained in the container
- with any list widget that knows "Items" and "Current"

provided the appropriate data adapters have been created.

Hope this helps and thank you for your interest.

BTW, I am cc-ing this to the boost mailing list

Regards

Hajo

Speed up GUI coding by a factor of 10x
http://www.litwindow.com/library