WPF MutiDataTrigger not firing setter

Question

I'm trying to use MultiDataTriggers to enabled/disable a button based on the value of two text boxes.

The docs state that the conditions in a MultiDataTrigger are logically ANDed together. In the example below if txtFirst.Text is foo and txtSecond.Text is bar I'd like to enable the button. However, the button always stays disabled (IsEnabled=false).

I'm sure I'm missing a trick here, but a thorough search of Google hasn't gotten me anywhere....

<StackPanel>
     <Button IsEnabled="False" Content="OK">
      <Button.Style>
       <Style>
        <Style.Triggers>
         <MultiDataTrigger>
          <MultiDataTrigger.Conditions>
           <Condition Binding="{Binding ElementName=txtFirst, Path=Text}" Value="foo"/>
           <Condition Binding="{Binding ElementName=txtSecond, Path=Text}" Value="bar"/>
          </MultiDataTrigger.Conditions>
          <Setter Property="Button.IsEnabled" Value="True"/>
         </MultiDataTrigger>
        </Style.Triggers>
       </Style>
      </Button.Style>
     </Button>

     <TextBox x:Name="txtFirst"/>
     <TextBox x:Name="txtSecond"/>
    </StackPanel>

Answer 1

Setting a property directly on the object itself overrides any style-triggered settings. Change your button declaration to:

<Button Content="OK">
    <Button.Style>
        <Style>
            <Setter Property="IsEnabled" Value="False"/>
            <Style.Triggers>

Now that the IsEnabled property is set in the style, the trigger can change it. Don't ask me why. :)