Question

Please help me, i am new to WP7 development.I have a class like this in code behind page(.xaml.cs):

public class NullVisibilityConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return value == null ? Visibility.Collapsed : Visibility.Visible;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            Visibility? v = value as Visibility?;
            return ((v.HasValue) || (v.Value == Visibility.Collapsed)) ? null : "";
        }
    }

I have a .xaml file is like this:

<ListBox ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Disabled" x:Name="lstImages" HorizontalAlignment="Center" ItemsSource="ImageList" Padding="0" Margin="0" BorderThickness="0"  >
                                        <ListBox.ItemTemplate>
                                            <DataTemplate>
<Image x:Name="imgSe" Visibility="{Binding Default, Converter={StaticResource NullVisibilityConverter}}" Height="50" Source="../Assets/g1.png"></Image>
 </DataTemplate>
                                        </ListBox.ItemTemplate>
                                    </ListBox>

So Default is a class in ImageList(IList), So if Default is Null then i have to hide the Image and if Default is not null then i have to show that image. I have tried the above code but my app is crashing. I am getting warning as “the resource NullVisibilityConverter could not be resolved” in .xaml page.

Thanks in advance.

Answer 1

You need to create an instance of your value converter within your page resources as follows. Note, the use of xmlns which maps your C# namespace to an XML namespace:

<phone:PhoneApplicationPage 
   xmlns:conv="clr-namespace:ConverterNamespace"
   ...
   >

    <phone:PhoneApplicationPage.Resources>
        <conv:NullVisibilityConverter x:Key="VisibilityConverter"/>
    </phone:PhoneApplicationPage.Resources>
  ...
</phone:PhoneApplicationPage>

Now reference it as follows, note the conv prefix defined above:

<Image x:Name="imgSe" Visibility="{Binding Default, Converter={StaticResource VisibilityConverter}}" />