...
     < radW:RadWindow         
           VisibleOnPageLoad = "true"
           OffsetElementId = "HtmlButton"
           OpenerElementId="HtmlButton"
           Runat ="server"  
></ radW:RadWindow >  

      < radW:RadWindow           
           VisibleOnPageLoad = "true"
           OffsetElementId = " <% # ServerButton.ClientID %> "
           OpenerElementId="<%# ServerButton.ClientID %> "
           Runat="server" 
      ></radW:RadWindow>

The second RadWindow uses the Page's binding mechanism, and because of this it is mandatory that the Page.DataBind() method is called (for example at the end of the Page_Load method).

e.g.: this.Page.DataBind();

 

Setting the VisibleOnPageLoad property to true will automatically make the window visible when the page loads

 

2. Windows can be shown relative to an html element .
Using the OffsetElementId  allows for fine-grained control over the position of a window relative to the rest of the page element flow. This allows for flexible declarative relative positioning that is independent of the screen-size and automatically adjusts to the changes in the page layout. The property should specify the id of an HTML element, whose top left corner will be used by the window object to positions itself relatively. The offset can be additionally tuned using the Top and Left properties (to specify offsets in pixels).

3.Codeless opening of windows

While windows can be easily opened uisng the clientside JavaScript API, RadWindow also goes a step further in easing the developer.
Using the OpenerElementId  property it is possible to specify the id of an HTML element that, when clicked, will automatically open the particular RadWindow object.

Note: The OpenerElementId  is of string type and expects to receive the client-side ID of the element. That is, if a server-side ASP.NET control is used (such as Button, Label, Link or another), its ClientID propety should be specified. This can be done declaratively in the following manner: