WPF - Enable/Disable tabstop based on whether property has data

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 h开发者_C百科andle 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>

---

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