Saturday, 25 February 2012

Datagrid loading message and VisualBrush

I have to load a DataGrid from a slow running DB query. To keep the UI responsive I'm running the data retrieval on a worker thread but I wanted an inobtrusive message to be displayed to the User during the loading phase. I replaced the DataGrid's Background with a TextBlock contained in VisualBrush. With the TextBlock's Text and Visibility bound to the underlying ViewModel. For those cases where there is no data to be shown in the DataGrid I show an alternate message.
<DataGrid ItemsSource="{Binding Source{StaticResource ViewModel},Path=EnrolledStudents}"
            CanUserAddRows="False"
            CanUserDeleteRows="False"
            AutoGenerateColumns="False"
            IsReadOnly="True">
   <DataGrid.Background>
      <VisualBrush Stretch="None">
         <VisualBrush.Visual>
            <StackPanel Background="White">
               <TextBlock HorizontalAlignment="Center"
                           VerticalAlignment="Center"
                           FontSize="10pt"
                           Margin="2"
                           Foreground="Red"
                           Text="{Binding Path=Strings.V_LabelLoading}"
                           Visibility="{Binding Source{StaticResource ViewModel}, Path=EnrolledStudentLoadingInProgress, Converter={StaticResource boolToCollapsedVisibilityConverter}}" />
               <TextBlock HorizontalAlignment="Center"
                           VerticalAlignment="Center"
                           FontSize="10pt"
                           Margin="2"
                           Foreground="Silver"
                           Text="{Binding Path=Strings.V_LabelNoEnrolledStudents}"
                           Visibility="{Binding Source{StaticResource ViewModel}, Path=NoEnrolledStudents, Converter={StaticResource boolToCollapsedVisibilityConverter}}" />
            </StackPanel>
         </VisualBrush.Visual>
      </VisualBrush>
   </DataGrid.Background>
   <DataGrid.Columns>

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