绑定按钮IsEnabled到ComboBox选择

Question

I know this can be done in a converter, but I'd like to disable a button based on a particular item selected in a ComboBox, using only XAML.

The following below works, using the Visibility property. How come if I try to use IsEnabled it does not work? Is there something I'm missing? If that's the way it is, if someone could explain why, that would be great. Should I just always use converters?

<ComboBox Name="WidthTypeComboBox" 
    ItemsSource="{Binding Source={StaticResource WidthType}}" 
    SelectedItem="{Binding WidthTypeSelected}" />

Works:

<Button Content="Map Channels" Command="{Binding ShowChannelAction}">
    <Button.Style>
        <Style TargetType="Button">
            <Style.Triggers>
                <DataTrigger Binding="{Binding SelectedIndex, 
                    ElementName=WidthTypeComboBox}" Value="0">
                    <Setter Property="Visibility" Value="Visible" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

Does not work:

<Button Content="Map Channels" Command="{Binding ShowChannelAction}">
    <Button.Style>
        <Style TargetType="Button">
            <Style.Triggers>
                <DataTrigger Binding="{Binding SelectedIndex, 
                    ElementName=WidthTypeComboBox}" Value="0">
                    <Setter Property="IsEnabled" Value="True" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

Answer 1

I'm actually not sure how the first one is working. It depends on what you've set for the properties on your button. Usually you need a default setter in the style and to remove any IsEnabled value set locally on the button:

<Style TargetType="Button">
    <Setter Property="IsEnabled" Value="False" />
    <Style.Triggers>
        <DataTrigger Binding="{Binding SelectedIndex, 
            ElementName=WidthTypeComboBox}" Value="0">
            <Setter Property="IsEnabled" Value="True" />
        </DataTrigger>
    </Style.Triggers>
</Style>

It comes down to the precedence of where the property value is set. For example, property values set locally override style setter/triggers. This article explains dependency property precendence with some examples.