How do I create a ProgressBar which is hidden when the Value is 0?

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="开发者_运维知识库{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>

Try setting the ProgressBar's Visibility property in its ValueChanged event:

private void progressBar1_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) {
    progressBar1.Visibility = (progressBar1.Value == 0) ? Visibility.Hidden : Visibility.Visible;
}

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.

Example XAML:

<ProgressBar>
    <ProgressBar.Resources>
        <src:DoubleToVisibilityConverter x:Key="_doubleToVisibilityConverter" />
    </ProgressBar.Resources>
    <ProgressBar.Visibility>
        <Binding
            RelativeSource="{RelativeSource Self}"
            Path="Value"
            Converter="{StaticResource _doubleToVisibilityConverter}"
        />
    </ProgressBar.Visibility>
</ProgressBar>

And code:

public class DoubleToVisibilityConvertor : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        double input = 0;

        if (value is double)
        {
            input = (double)value;
        }
        else if (value is int)
        {
            input = (int)value;
        }
        else if (value is string) // Useful if input of converter is written in XAML
        {
            if (!double.TryParse((string)value, out input))
                return Binding.DoNothing;
        }
        else
        {
            return Binding.DoNothing;
        }

        return (input > 0 ? Visibility.Visible : Visibility.Collapsed);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return Binding.DoNothing;
    }
}

Disclaimer: written from memory, not compiled or tested.