Binding DataTemplate Column BackGround Color to IvalueConverter

Question

I have a WPF datagrid and have a datatemplate column called "Requested Date Out Source." The application should look at the date in the cell and change the color based on if it's today, past, or future.

I have the Ivalueconverter:

public class FBrushConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            string input = value as string;
            {
                if (input == "Select a date")
                {
                    return new SolidColorBrush(Colors.Black);
                }
                else
                {
                    DateTime dt = System.Convert.ToDateTime(input);
                    switch (true)
                    {
                        case true when (dt == DateTime.Today):
                            return new SolidColorBrush(Colors.Yellow);
                        case true when (dt < DateTime.Today):
                            return new SolidColorBrush(Colors.Red);
                        case true when (dt > DateTime.Today):
                            return new SolidColorBrush(Colors.Blue);
                        default:
                            //return Brushes.Black;
                            return new SolidColorBrush(Colors.Black);
                    }
                }
            }
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotSupportedException();
        }

I have the XAML:

<DataGridTemplateColumn x:Name="DateoutSource" Header="Requested &#x0a; Date Out Source" Width="125" SortMemberPath="DateOutSource" SortDirection="Ascending" >
                       <DataGridTemplateColumn.CellTemplate>                       
                            <DataTemplate>
                            <DatePicker x:Name="BtnDateOutSource" SelectedDate="{Binding DateOutSource}" SelectedDateChanged="BtnDateOutSource_SelectedDateChanged" Foreground="{Binding Converter={StaticResource FBrushConverter}}">                               
                            </DatePicker>
                            </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>

The result is that the column is always red:

Tracing through the code indicates that the Convert Object value is always NULL which is why the display is always red.

This implies some issues with the binding. I have tried a variety of approaches with no luck.

Any ideas on this one? Thanks in Advance, Kerry

Answer 1

Bind the Foreground property to DateOutSource property as suggested by @Xiaoy312:

Foreground="{Binding DateOutSource, Converter={StaticResource FBrushConverter}}"

Then you also need to modify your converter to cast the value to a DateTime? which I assume is the actual type of DateOutSource:

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    DateTime? dt = (DateTime?)value;
    if (!dt.HasValue)
        return new SolidColorBrush(Colors.Black);

    DateTime date = dt.Value.Date;
    if (date == DateTime.Today)
        return new SolidColorBrush(Colors.Yellow);
    else if (date < DateTime.Today)
        return new SolidColorBrush(Colors.Red);
    else if (date > DateTime.Today)
        return new SolidColorBrush(Colors.Blue);

    return new SolidColorBrush(Colors.Black);
}