Using binding to XML in Silverlight

Question

I'm currently having trouble binding XML to a GUI in a Silverlight application. Especially with TwoWay-Binding.

As we know it is really easy to do in a Windows client application using WPF. There you can just do something like:

XML:

<person>
  <firstname>Test</firstname>
  <surname>Test</surname>
  <email>[email protected]</email>
</person>

and a XAML page viewing a Grid to edit (Binding using either XLinq or XPath):

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
        <ColumnDefinition Width="3*" />
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="30" />
        <RowDefinition Height="30" />
        <RowDefinition Height="30" />
        <RowDefinition Height="221*" />
    </Grid.RowDefinitions>
    <TextBlock Grid.Column="0" Grid.Row="0" Text="First name:" />
    <TextBox Grid.Column="1" Grid.Row="0" Text="{Binding Path=Element[firstname].Value, Mode=TwoWay}" />
    <TextBlock Grid.Column="0" Grid.Row="1" Text="Surname:" />
    <TextBox Grid.Column="1" Grid.Row="1" Text="{Binding Path=Element[surname].Value, Mode=TwoWay}" />
    <TextBlock Grid.Column="0" Grid.Row="2" Text="EMail:" />
    <TextBox Grid.Column="1" Grid.Row="2" Text="{Binding Path=Element[email].Value, Mode=TwoWay}" />
</Grid>

Because of the TwoWay-Mode the user writes directly into the XML.

However, in Silverlight there is no option to bind like in the example above. But Microsoft added the XPathEvaluate-Method() in Silverlight 4.

So I was trying to bind the complete XDocument to every TextBox and use a converter along with the ConverterParameter to pass a XPath expression and evaluate it.

<Grid x:Name="LayoutRoot">
    <TextBlock Text="{Binding Path=Data, Converter={StaticResource TestKonverter}, ConverterParameter=//firstname, Mode=TwoWay}" FontSize="20" />
</Grid>

and...

public class XMLConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var __doc = (XDocument)value;
        var __xpath = (IEnumerable)__doc.XPathEvaluate(parameter.ToString());

        return (__xpath.Cast<XElement>().FirstOrDefault());
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        //getting the attached XDocument again as __doc ?!
        var __xpath = (IEnumerable)__doc.XPathEvaluate(parameter.ToString());

        (__xpath.Cast<XElement>().FirstOrDefault()).Value = value.ToString();

        return value;
    }
}

To get some kind of TwoWay-Binding, I thought of using the XPath-Expression to get the correct Node and write the new value in it. The problem is, in the ConvertBack-Method() I don't see a way how to get the XDocument. Is there any way to get the XDocument through the given parameters in ConvertBack, without making it somewhere as static?

Christoph Christoph · Accepted Answer · 2011-03-22T10:02:25

Thanks for your answer.

About two weeks ago I solved this problem, by just creating a new class called XTextBox. I simple inherit from TextBox and create two DependencyProperties with the types XElement and string in the new class.

In my XAML I can use binding as i did before and hand over the complete XElement and the XPath to find the right node to my control.

<custom:XTextBox Data="{Binding Path=XValues, Mode=TwoWay}" XPath="//Measurements/Headline/Fontsize" />

Aside from the two DependencyProperties I use a normal TextChanged Event to update the Value in the XElement using the XPath again.

This completley solves TwoWay Binding, because I never have to create a new XElement and copy anything around. I also implemented XComboBox, XRadioButton and XCheckBox, which is enough in my case.

Using binding to XML in Silverlight

2 Answers