通过ComboBox TwoWay绑定更改数据源中的XML属性

Question

This is my XAML sample code:

<Grid>
    <Grid.DataContext>
        <XmlDataProvider x:Name="DataProvider" Source="datacontext.xml" XPath="/"  />
    </Grid.DataContext>
    <ComboBox Name="combobox1" Width="100" Height="25" ItemsSource="{Binding XPath=Contact/ContactMethods//*}">
        <ComboBox.SelectedValue>
            <Binding XPath="Contact\ContactMethods/*[@Selected='True']" NotifyOnSourceUpdated="True" NotifyOnTargetUpdated="True" />
        </ComboBox.SelectedValue>
    </ComboBox>
</Grid>

This is my XML data source:

<Contact ShowsInterest="true">
  <Name>John</Name>
  <Lastname>Doe</Lastname>
  <ContactMethods>
    <ContactMethod Selected="False">Phone</ContactMethod>
    <ContactMethod Selected="False">Email</ContactMethod>
    <ContactMethod Selected="True">Letter</ContactMethod>
    <ContactMethod Selected="False">Mobile</ContactMethod>
  </ContactMethods>
</Contact>

The code above displays the contacts methods as the combobox. The ContactMethod which has the XML Selected Attribute set to true is preselected in the combobox and displayed at startup.

It looks like this:

I use the following method to save the data:

private void OnSubmitClick(object sender, System.EventArgs eventArgs)
{
    DataProvider.Document.Save("datacontext.xml");
}

This method changes the value of the ContactMethod and not the Selected Attribute.

If you select Mobile and click [submit] the result looks like this:

  <ContactMethods>
    <ContactMethod Selected="False">Phone</ContactMethod>
    <ContactMethod Selected="False">Email</ContactMethod>
    <ContactMethod Selected="True">Mobile</ContactMethod>
    <ContactMethod Selected="False">Mobile</ContactMethod>
  </ContactMethods>

The change is persisted where the Selected Attribute equals true. The value which the control was bound to is overwritten.

Desired Result: it should look like this:

  <ContactMethods>
    <ContactMethod Selected="False">Phone</ContactMethod>
    <ContactMethod Selected="False">Email</ContactMethod>
    <ContactMethod Selected="False">Letter</ContactMethod>
    <ContactMethod Selected="True">Mobile</ContactMethod>
  </ContactMethods>

Question: How do i change the Selected Attribute of the currently selected item? Is it possible to persist the changes made with the desired xml data structure?

Answer 1

Why don't you do something like this: instead of having multiple Selected attributes just create a Selected attribute in ContactMethods element:

<Contact ShowsInterest="true">
  <Name>John</Name>
  <Lastname>Doe</Lastname>
  <ContactMethods Selected="Phone">
    <ContactMethod>Phone</ContactMethod>
    <ContactMethod>Email</ContactMethod>
    <ContactMethod>Letter</ContactMethod>
    <ContactMethod>Mobile</ContactMethod>
  </ContactMethods>
</Contact>

Then just bind your ComboBox like this:

    <ComboBox Name="combobox1" Width="100" Height="25" ItemsSource="{Binding XPath=Contact/ContactMethods/ContactMethod}"
             IsSynchronizedWithCurrentItem="True" 
             SelectedValue="{Binding XPath=Contact/ContactMethods/@Selected}">
    </ComboBox>

Another option without changing the source XML structure : The idea is to alter the XML at the time of persistence setting the selected attribute flag to the ComboBox SelectedValue :

Change your OnSubmitClick method to:

    private void OnSubmitClick(object sender, RoutedEventArgs e)
    {
        XElement xe = XElement.Load(new XmlNodeReader(DataProvider.Document));
        var elements = xe.Elements("ContactMethods").Elements("ContactMethod").ToList();
        var sel = combobox1.SelectedValue;
        foreach(XElement element in elements)
        {
            element.SetAttributeValue("Selected", (string)sel == element.Value ? "True" : "False");
        }
        xe.Save("datacontext.xml");
        //DataProvider.Document.Save("datacontext.xml");
    }

And your ComboBox definition to:

       <ComboBox Name="combobox1" Width="100" Height="25" ItemsSource="{Binding XPath=Contact/ContactMethods/ContactMethod}"
             IsSynchronizedWithCurrentItem="True" 
             SelectedValue="{Binding XPath=Contact/ContactMethods/ContactMethod[@Selected\=\'True\'],Mode=OneTime}">
        </ComboBox>