wpf - ScrollViewer to dynamically fetch new rows when reaching the bottom -

i wish create scrollviewer shows vertical scrollbar regardless of whether has items scroll down or not. doing this, seek dynamically fetch more data db user scrolls towards bottom. data stored in datagrid (dggrid), , wrapped scrollviewer (svmain) (see below). data db retrieved using a method triggers on scrollviewer.scrollchanged event.

<scrollviewer grid.row="0" verticalscrollbarvisibility="visible" dockpanel.dock="top"  name="svmain" cal:message.attach="[event scrollchanged] = [action scrollmaster($eventargs)]">                         <stackpanel>                             <grid visibility="{binding path=isformview, converter={staticresource booleantovisibilityconverter}}">                                 <grid.columndefinitions>                                     <columndefinition width="200"/>                                     <columndefinition width="200"/>                                     <columndefinition width="200"/>                                     <columndefinition width="200"/>                                     <columndefinition width="200"/>                                 </grid.columndefinitions>                                  <grid.rowdefinitions>                                     <rowdefinition />                                     <rowdefinition />                                 </grid.rowdefinitions>                                  <stackpanel grid.row="0" grid.column="0" orientation="horizontal">                                     <checkbox ischecked="{binding masterdto.activeflag, mode=twoway, updatesourcetrigger=propertychanged}"/>                                     <label content="active"/>                                 </stackpanel>                                  <stackpanel grid.row="1" grid.column="0">                                     <con:mandatorylabel text="country id" />                                     <textbox text="{binding masterdto.countryid, mode=twoway, updatesourcetrigger=propertychanged}"/>                                 </stackpanel>                                 <stackpanel grid.row="1" grid.column="1">                                     <con:mandatorylabel text="currency"/>                                     <textbox text="{binding masterdto.currency, mode=twoway, updatesourcetrigger=propertychanged}"/>                                 </stackpanel>                             </grid>                              <!-- grid view -->                             <dockpanel visibility="{binding path=isgridview, converter={staticresource booleantovisibilityconverter}}">                                 <datagrid name="dggrid" style="{staticresource readonlydatagrid}" selecteditem="{binding path=masterdto, mode=twoway}" itemssource="{binding masterdtos, mode=twoway, updatesourcetrigger=propertychanged}" cal:message.attach="[event selectionchanged] = [action gridselect]">                                     <datagrid.columns>                                         <datagridtemplatecolumn header="active">                                             <datagridtemplatecolumn.celltemplate>                                                 <datatemplate>                                                     <controls:yesnolabel value="{binding activeflag}" />                                                 </datatemplate>                                             </datagridtemplatecolumn.celltemplate>                                         </datagridtemplatecolumn>                                         <datagridtextcolumn header="country id" binding="{binding countryid}"/>                                         <datagridtextcolumn header="currency" binding="{binding currency}"/>                                     </datagrid.columns>                                 </datagrid>                             </dockpanel>                          </stackpanel>                     </scrollviewer> 

the problem though set verticalscrollbarvisibility property of scrollviewer visible (and vertical scrollbar shown @ times), scrollbar disabled , there no scroll thumb visible whenever amount of data in datagrid fits height of screen. if resize screen smaller size, vertical scrollbar enabled , can move thumb around. however, want scrollbar , thumb enabled regardless of whether the content of viewport can accommodate contents or not. can provide on this?

thanks!

you play around icollectionview interface. every time ienumerable bound itemscontrol, default view implicitly inserted between source , target objects. tracks current item, has support sorting, grouping, etc. implement own collection view supports loading further items when last element reached.