CODEWITHSUNDEEP
silverlightwindows-phone-7xamlwindows-store-apps
Ross Dargan
Ross Dargan

Reputation: 6021

Show a textblock if an ObservableCollection is Empty

I want to show a textblock that says "you have no data" when a collection that should be shown is empty.

I can easily get this to work on page load by using a converter, but since that doesn't get notified when the collection data changes the code doesn't work:-

TextBlock Visibility="{Binding Devices, Converter={StaticResource EmtpyListToVisibility}, Mode=OneWay}" Text="You have no devices added, please press the Add Device button on the application bar" TextWrapping="Wrap"></TextBlock>

<phone:LongListSelector Margin="0,12,0,0" ItemsSource="{Binding Devices, Mode=OneWay}" ItemTemplate="{StaticResource DeviceTemplate}" LayoutMode="List" VerticalAlignment="Top" >                       
</phone:LongListSelector>

In windows 8 apps I have added a property called xxxHasRecords, then I subscribe to the Observable collections CollectionChanged event and used the property notification so my UI can be updated. I find myself writing this code so often that there just has to be a better way of handling it!

Thanks

Ross

Upvotes: 3

Views: 2757

Answers (2)

Jehof
Jehof

Reputation: 35544

In this case i use a BooleanToVisibilityConverter

public class BooleanToVisibilityConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        bool invert = false;

        if (parameter != null)
        {
            invert = System.Convert.ToBoolean(parameter);
        }

        bool isVisible = System.Convert.ToBoolean(value);

        if (invert)
        {
            isVisible = !isVisible;
        }

        return isVisible ? System.Windows.Visibility.Visible : System.Windows.Visibility.Collapsed;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        Visibility result = (Visibility)Enum.Parse(typeof(Visibility), value.ToString(), true);

        return result == Visibility.Visible ? true : false;
    }
}

And change the binding of the Visibility property of the TextBox to the following:

<TextBlock Visibility="{Binding Devices.Count, Converter={StaticResource boolToVisibilityConverter}, Mode=OneWay}"
    Text="You have no devices added, please press the Add Device button on the application bar"
    TextWrapping="Wrap">
</TextBlock>

When the collection is empty Count returns the value 0. The Converter uses System.Convert.ToBoolean which converts 0 to false and all other values to true.

False is returned as Visibility.Collapsed and true as Visibility.Visible.

Upvotes: 1

ColinE
ColinE

Reputation: 70162

Rather than bind to the ObservableCollection, you should bind to the ObservableCollection.Count property. The collection implements INotifyPropertyChanged, so will notify your bindings whenever its size changes. Your value converter then simply has to check for zero.

Upvotes: 7

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