Binding a separate data source within a bound datatemplate

Question

I have the following simple datatemplate within a flipview.

<FlipView x:Name="MyFlipview" ItemsSource="{x:Bind Path=ViewModel.Fleas}" >
       <FlipView.ItemTemplate>
            <DataTemplate  x:DataType="types:FleaType">     
               <TextBox x:Name ="Header" Text= "{Binding Path = ViewModel.GeneralComment}"></TextBox> 
               <TextBox x:Name ="FleaName" Text= "{Binding Path = FleaName}"></TextBox>

            </DataTemplate>
       </FlipView.ItemTemplate>
</FlipView>

But I dont know how to bind the Header textbox to generalcomment on the viewmodel as Generalcomment isnt part of the fleas collection. If anyone knows how to accomplish this it'd be much appreciated.

Thanks

Answer 1

You're looking for RelativeSource:

<FlipView x:Name="MyFlipview" ItemsSource="{x:Bind Path=ViewModel.Fleas}" >
       <FlipView.ItemTemplate>
            <DataTemplate  x:DataType="types:FleaType">     
               <TextBox x:Name ="Header" Text= "{Binding RelativeSource={RelativeSource AncestorType=UserControl}, Path=DataContext.GeneralComment}"></TextBox> 
               <TextBox x:Name ="FleaName" Text= "{Binding Path = FleaName}"></TextBox>

            </DataTemplate>
       </FlipView.ItemTemplate>
</FlipView>

There's more info here: RelativeSource on MSDN, essentially what this is doing is saying "Find the UserControl element above me, and bind to its DataContext which will be the view model, and then the GeneralComment property"; obviously if you're using something other than UserControl (e.g. a Page etc) then replace it with that type.

---

The One Where UWP Decides It Wants To Be Different.

As GeorgeT has indicated, AncestorType isn't supported in UWP, as such there's a way around this as explained here: How to do relativesource mode find ancestor (or equivalent) in UWP

The way I'd probably do it is to just set a name for the user control, and then do:

{Binding ElementName=MyUserControl, Path=DataContext.GeneralComment}