Is it Possible to apply a DataTemplate to a Page?

Question

I'm trying to follow the MVVM pattern laid out here: http://msdn.microsoft.com/en-us/magazine/dd419663.aspx#id0090097 I have this in my MainWindowResources.xaml file:

<DataTemplate DataType="{x:Type vm:VendorsViewModel}">
        <vw:Vendors/>  <--- I get a "Can't put a page in a style" error in blend with this
</DataTemplate>

and I've got this in my MainWindow.xaml file

<Window.Resources>
     <ResourceDictionary Source="MainWindowResources.xaml"/>
</Window.Resources>

The mainWindow.xaml file contains a menu on the left and page holder on the right. Can I apply a dataTemplate to a <Page>? Or does it have to be a <UserControl>? As it stands, nothing is being data bound, here's what I have on the page that I want to have the viewmodel applied to:

<Custom:DataGrid Margin="0,30,0,0" d:LayoutOverrides="Width" ItemsSource="{Binding Path=AllVendors, Mode=Default}" >
     <Custom:DataGrid.Columns>
    <Custom:DataGridTextColumn Header="Company Name" Binding="{Binding Path=Name}" />
    </Custom:DataGrid.Columns>
</Custom:DataGrid>

Answer 1

DataTemplates are applied to Content, which in most cases is either the Content property of a ContentControl or the Items/ItemsSource property of an ItemsControl. Page is not derived from ContentControl (UserControl is) so a DataTemplate can't be applied to its Content.

From what you're doing here it doesn't sound like that's what you're trying to do though. It looks like you're trying to use a Page in a DataTemplate which is what the error is telling you. Page is treated like Window in that it is a root container that is intended to have visual Content defined in a xaml file. UserControl has a similar purpose but can be inserted anywhere into a layout. If you change vw:Vendors to be a UserControl that should get rid of this specific error but you should also consider whether you're gaining anything from having the UserControl instead of just putting its content directly into the DataTemplate - this can help discourage code-behind and force you to use your ViewModel correctly.