DataTrigger where value is NOT null?
This is a bit of a cheat but I just set a default style and then overrode it using a DataTrigger if the value is null...
<Style>
<!-- Highlight for Reviewed (Default) -->
<Setter Property="Control.Background" Value="PaleGreen" />
<Style.Triggers>
<!-- Highlight for Not Reviewed -->
<DataTrigger Binding="{Binding Path=REVIEWEDBY}" Value="{x:Null}">
<Setter Property="Control.Background" Value="LightIndianRed" />
</DataTrigger>
</Style.Triggers>
</Style>
I ran into a similar limitation with DataTriggers, and it would seem that you can only check for equality. The closest thing I've seen that might help you is a technique for doing other types of comparisons other than equality.
This blog post describes how to do comparisons such as LT, GT, etc in a DataTrigger.
This limitation of the DataTrigger can be worked around to some extent by using a Converter to massage the data into a special value you can then compare against, as suggested in Robert Macnee's answer.
You can use an IValueConverter for this:
<TextBlock>
<TextBlock.Resources>
<conv:IsNullConverter x:Key="isNullConverter"/>
</TextBlock.Resources>
<TextBlock.Style>
<Style>
<Style.Triggers>
<DataTrigger Binding="{Binding SomeField, Converter={StaticResource isNullConverter}}" Value="False">
<Setter Property="TextBlock.Text" Value="It's NOT NULL Baby!"/>
</DataTrigger>
</Style.Triggers>
</Style>
</TextBlock.Style>
</TextBlock>
Where IsNullConverter is defined elsewhere (and conv is set to reference its namespace):
public class IsNullConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return (value == null);
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new InvalidOperationException("IsNullConverter can only be used OneWay.");
}
}
A more general solution would be to implement an IValueConverter that checks for equality with the ConverterParameter, so you can check against anything, and not just null.