Question

I would like to make WPF Window that contains DataGrid control and enables following scenario in C# WPF DataGrid: Data is loaded in DataGrid, application validates data in background (parallel async operations), when row is determined to be valid its bacground color becomes green, red otherwise. What is cleanest way to program this behaviour? Is there any built-in functionality in DataGrid and WPF to do this kind of validation?

EDIT:
For now I have manged to perform this by using RowStyle, but this makes application non responsive because validation takes time for each row, so I would like to make this async and parallel.

<DataGrid.RowStyle>
    <Style TargetType="{x:Type DataGridRow}">
        <Setter Property="Background" Value="{Binding BgColor}">
        </Setter>
    </Style>
</DataGrid.RowStyle>

EDIT2:
Here is progress:

<DataGrid.RowStyle>
    <Style TargetType="{x:Type DataGridRow}">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=BgColor}" Value="DarkRed">
                <Setter Property="Background" Value="DarkRed"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</DataGrid.RowStyle>

Code behind looks like this:

Func<List<bool>> func = () => data.AsParallel().Select(x => File.Exists(x.FullPath)).ToList();
List<bool> res = null;
IAsyncResult ar = func.BeginInvoke(new AsyncCallback(x=>
{
    res = ((Func<List<bool>>)((AsyncResult)x).AsyncDelegate).EndInvoke(x);
    for (int i = 0; i < res.Count; ++i)
        if (!res[i])
            data[i].BgColor = Brushes.DarkRed;
}), null);

Remaining problem is that row background color is refreshed only when row is redrawn (moved out of view and than into view again). Any clean and easy way to fix this?

EDIT3:
Finally everything works exactly as required, only thing missing in EDIT2 was to implement INotifyPropertyChanged in data source class.

Answer 1

Well the best approach would be using a DataTrigger in the style of the DataGridItems and provide a property (bool?) in the ViewModel which is bound to the DataTrigger. In the DataTrigger you could declare the visual for all three states Null, True, False

For additional information on DataTrigger, please have a look here.

Edit

Hmm, any chance to put the highlighting functionality in a DataTemplate? I implemented a highlighting for the selection state of an entity. And it works as expected.

<DataTemplate.Triggers>
  <DataTrigger Binding="{Binding IsSelected, RelativeSource={RelativeSource AncestorType=ListBoxItem}}"
                  Value="true">
  <!-- Expand -->
  <DataTrigger.EnterActions>
    <BeginStoryboard>
      <Storyboard Storyboard.TargetName="CommandPanel">
        <DoubleAnimation Duration="0:0:0.200" Storyboard.TargetProperty="Opacity" To="1" />
        <DoubleAnimation Duration="0:0:0.150" Storyboard.TargetProperty="Height"
                            To="{StaticResource TargetHeightCommandPanel}" />
      </Storyboard>
    </BeginStoryboard>
  </DataTrigger.EnterActions>
  <!-- Collapse -->
  <DataTrigger.ExitActions>
      <BeginStoryboard>
        <Storyboard Storyboard.TargetName="CommandPanel">
          <DoubleAnimation Duration="0:0:0.100" Storyboard.TargetProperty="Opacity" To="0" />
          <DoubleAnimation Duration="0:0:0.150" Storyboard.TargetProperty="Height" To="0" />
        </Storyboard>
      </BeginStoryboard>
    </DataTrigger.ExitActions>
  </DataTrigger>
</DataTemplate.Triggers>

Btw, have you ever heard of MVVM?