Question

I need to set the tabstop of a textbox based on whether or not the bound property has data or not. The properties are nearly all strings – I want to disable the tabstop if the property is null or empty.

I am using a style for these textboxes.

Here is the style I am currently using:

<Style TargetType="TextBox" x:Key="FauxLabel">
    <Setter Property="Background" Value="Transparent" />
    <Setter Property="IsTabStop" Value="True" />
    <Setter Property="IsReadOnly" Value="True" /> 
    <!-- rest of setters truncated -->
</Style>

And here is an example of my usage:

<TextBox
    Name="Account"
    Style="{StaticResource ResourceKey=FauxLabel}"
    Text="{Binding
        Path=SelectedItem.AccountNumber,
        ElementName=CrfResults}"/>

In this exmple, if the AccountNumber property is null or empty, I want to disable the tabstop. I am using Visual Studio 2010 and .Net 4.0. Can anyone help me out?

Update:

Thanks to Rachel for her answer. I was able to update the style to handle all textboxes using that style using by adding the trigger below which binds to the text property, rather than the underlying bound property:

        <Style.Triggers>
            <Trigger Property="Text" Value="{x:Null}">
                <Setter Property="IsTabStop" Value="False">                            
                </Setter>
            </Trigger>
            <Trigger Property="Text" Value="">
                <Setter Property="IsTabStop" Value="False">
                </Setter>
            </Trigger>
        </Style.Triggers>

Answer 1

Use a DataTrigger which checks if the value is {x:Null}

<Style TargetType="TextBox" x:Key="FauxLabel">
    <Setter Property="IsTabStop" Value="True" />
    <Style.Triggers>
        <DataTrigger Property="{Binding ElementName=CrfResults, Path=SelectedItem.AccountNumber}" Value="{x:Null}">
            <Setter Property="IsTabStop" Value="False" />
        </DataTrigger>
    </Style.Triggers>
</Style>

You could probably do it with a regular Trigger instead of a DataTrigger too