WPF Trigger binding to MVVM property

Question

I have a datatemplate containing an image that I want to be hidden if the the value of a property in a ViewModel is true. Can anyone tell me why the the xaml below does not

Answer 1

I just did something similar using a ContentControl.

<ContentControl Content="{Binding CurrentListHasPendingChanges}">
  <ContentControl.ContentTemplate>
    <DataTemplate>
      <Image x:Name="img" Source="..\Images\List_16.png" Margin="0,0,5,0" Visibility="Hidden" />
      <DataTemplate.Triggers>
        <DataTrigger Binding="{Binding}" Value="False">
          <Setter Property="Image.Visibility" Value="Visible" />
        </DataTrigger>
      </DataTemplate.Triggers>
    </DataTemplate>
  </ContentControl.ContentTemplate>
</ContentControl>

From http://karlhulme.wordpress.com/2007/03/06/using-a-contentcontrol-and-datatemplate-to-indicate-new-andor-modified-data/

Answer 2

isn't that

<Setter Property="Visibility" Value="Hidden" />

?

I assume you use INotifyProptyChanged.

EDIT I did some Googling and I think you need to use some sort of template in order to make the trigger work.

eg.: http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/ae2dbfb7-5dd6-4352-bfa1-53634289329d

http://www.thejoyofcode.com/Help_Why_cant_I_use_DataTriggers_with_controls_in_WPF.aspx

Answer 3

Try removing "Image" part from Property="Image.Visibility" so you'll have:

<Setter Property="Visibility" Value="Hidden"/>

and add TargetType to your Style:

<Style TargetType="{x:Type Image}">

Answer 4

In my opinion we not need to use Triggers, with only the Binding it works well. To make binding to a property model, you can use BooleanToVisibilityConverter Is declared as follows:

<UserControl.Resources>
    <BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
</UserControl.Resources>

And how to use it is simple, just point to the key stated above:

<Image HorizontalAlignment="Left" Height="16"  VerticalAlignment="Center" Width="16" 
       Visibility="{Binding HasError, Converter={StaticResource BooleanToVisibilityConverter}}"
       Source="/myPath;component/Resources/Images/image1.png"/>

The property in the ViewModel:

private bool _hasError = false;
    public bool HasError
    {
        get { return !string.IsNullOrEmpty(_messageError); }
        set 
        {
            _hasError = value;                
            this.NotifyOfPropertyChange(() => this.HasError);
        }
    }