Change property depending on property in other control - WPF

Question

I want to use some kind of trigger to change a button in my window to IsEnabled = False when the textbox property Validation.HasErrors of my textbox is True.

Can I do this with Triggers of some kind on the Button?

If yes, some example would be nice!

Answer 1

Yes, you can do this with triggers, but because you are referring to another element, you must use a DataTrigger rather than a normal Trigger:

<Button>
  <Button.Style>
    <Style TargetType="Button">
      <Style.Triggers>
        <DataTrigger Binding="{Binding (Validation.HasError), ElementName=tb}" Value="True">
          <Setter Property="IsEnabled" Value="False" />
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </Button.Style>
</Button>

Note you must use a Style rather than the Button.Triggers collection, because Button.Triggers can contain only EventTriggers.

Answer 2

You can do this by using a Style. If you want to tie it directly to the text box, you could do something like this:

    <Style x:Key="DisabledOnErrors" TargetType="{x:Type Button}">
        <Style.Triggers>
            <DataTrigger Binding="{Binding (Validation.HasErrors)}" Value="True">
                <Setter Property="IsEnabled" Value="False"/>
            </DataTrigger>
        </Style.Triggers>
    </Style>

---

    <TextBox x:Name="myTextBox" />
    <Button Style="{StaticResource DisabledOnErrors}" 
            DataContext="{Binding ElementName=myTextBox}" />

This works if the button is not already binding to the DataContext for other properties. In this case, the Style is reusable for other button and text box pairings.