CODEWITHSUNDEEP
c#silverlightxaml
Nick Heiner
Nick Heiner

Reputation: 122442

Silverlight: Difficulty with binding to visiblity

I have two elements: a listbox and a "this list is empty" message. I'd like to bind their visibility to the list box's ItemsSource being empty. However, I'm not sure how to do this:

        <TextBlock Text="No favorite searches yet. Add some by searching, then clicking 'Add to Favorites'" 
                   Padding="10,0" 
                   VerticalAlignment="Center"
                   Visibility="{Binding Path=FavoriteFilters.IsEmpty, Converter={StaticResource visibilityConverter}}"
                   />

        <ListBox ItemsSource="FavoriteFilters" 
                 x:Name="favoriteFiltersList" 
                 Visibility="{Binding Path=FavoriteFilters.IsEmpty, Converter={StaticResource visibilityConverter}}">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <my:FavoriteFilterLink />
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

They are both visible, although the ItemsSource is empty. Also, I'm not sure how to invert the condition for the ListBox.

The visibility converter:

public class VisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value is bool?)
        {
            if (string.IsNullOrEmpty((string)parameter))
            {
                return (value as bool?).Value ? Visibility.Visible : Visibility.Collapsed;
            } else
            {
                return (value as bool?).Value ? Visibility.Collapsed : Visibility.Visible;
            }
        }
        throw new ArgumentException();
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Upvotes: 0

Views: 752

Answers (1)

ChrisF
ChrisF

Reputation: 137148

You might be better off writing two converters, one for the ListBox the other for the TextBlock. The logic of each would be simpler and you wouldn't need to pass a parameter to get the correct result.

While it might not be as elegant as a single converter solution it will be far more maintainable.

If you really want to pass a parameter then you need to use the ConverterParameter.

There's an example here but I'm not 100% sure it'll meet your requirements. The simplified XAML syntax is:

<TextBlock Visibility="{Binding FavoriteFilters.IsEmpty,
     Converter={StaticResource visibilityConverter}, ConverterParameter=false}"/>

<ListBox Visibility="{Binding FavoriteFilters.IsEmpty,
     Converter={StaticResource visibilityConverter}, ConverterParameter=true}"/>

Then in your converter (simplified):

bool show = (bool)value;
bool visible = (bool)parameter;
if (visible)
{
    return show ? Visibility.Visible : Visibility.Collapsed;
}
else
{
    return show ? Visibility.Collapsed : Visibility.Visible;
}

Upvotes: 1

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