Question

The following doesn’t quite work (ProgressValue is a value set in DataContext.)

<StatusBarItem Grid.Column="1">
    <StatusBarItem.Resources>
        <Style TargetType="ProgressBar">
            <Style.Triggers>
                <DataTrigger Binding="{Binding ProgressValue}" Value="0">
                    <Setter Property="Visibility" Value="Hidden"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </StatusBarItem.Resources>
    <ProgressBar Value="{Binding ProgressValue}" Grid.Column="1" Width="80" Height="13">
    </ProgressBar>
</StatusBarItem>

Answer 1

Try specifying a Minimum (and Maximum) value. After setting those it seems to work for my version of your code.

With this XAML:

    <StatusBarItem x:Name="Feedback" Grid.Row="1">
        <StatusBarItem.Resources>
            <Style TargetType="ProgressBar">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding}" Value="0">
                        <Setter Property="Visibility" Value="Hidden"/>
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </StatusBarItem.Resources>
        <ProgressBar Value="{Binding Mode=OneWay}" Minimum="0" Maximum="10" Grid.Column="1" Width="80" Height="13">
        </ProgressBar>
    </StatusBarItem>

and this code in the constructor of MainWindows.xaml.cs (for testing purposes only)

    int value = 10;
    public MainWindow()
    {
        InitializeComponent();
        Feedback.DataContext = value;

        Timer t = new Timer(500);
        t.Elapsed += (s, e) =>
            {
                if (value > 0) Dispatcher.Invoke(new Action(() => { Feedback.DataContext = --value; }));
                else t.Stop();
            };

        t.Start();
    }

I get the progress bar to go from 10 down to 0 at which point the progress bar disappears.