Hi Patricio,

To enable your composite user control to support the same design-time
function as the SplitContainer, you need to author a custom designer for
the composite user control to extend the design-time environment.

In detail, you extend the appearance of your custom design UI by
implementing a Glyph class and extend the behavior by implementing a
Behavior class. The Bahavior class is subordinate to the Glyph class. You
attach a Behavior object to a Glyph object in your Glyph type's constructor.

You override the GetHitTest method in the Glyph class to return a Cursor
object when the mouse pointer is over your glyph's hot spot. When the
design environment receives a value from your GetHitTest method that is not
null, it activates the Behavior object associated with your Glyph.

You override Behavior class methods like OnMouseDown to paint the selection
rectangle around the nested ListView control and set the primary selection
to this ListView control.

For more information on how to extend the appearance and behavior of
controls in design mode, please refer to the following MSDN document:
http://msdn2.microsoft.com/en-us/library/ms171820.aspx

Hope this helps.
If you have any question, please feel free to let me know.

Sincerely,
Linda Liu
Microsoft Online Community Support

Delighting our customers is our #1 priority. We welcome your comments and
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