Question

Continuing from my last question, I’d like to know how can I bind when a button is clicked (can this be done through pure XAML?) – or more simply, how can I do XAML-like binding through C# code?

EDIT: The previous question containing info:

I want to create a listbox that’ll be bound to XPath, relative to the other listbox’s currently selected item.

It’s using XmlDataProvider for the data, and the XML file looks like this:

<Programs>
    <Program name="...">
        <Step name="..."/>
        <Step name="..."/>
    </Program>
    <Program name="another">

    ...

</Programs>

So, the “parent” listbox is listing out all the programs, while “child” shows only Steps from the current Program.
I just need a pointer on the fact what’s such type of binding called.

Thanks in advance.

End of previous question

The question is how can I do a one time bind (I do not want binding to change as soon as user clicks another listbox item) when a button called “Load” is pressed?

Answer 1

Let’s start with an example where the detail list box does change whenever the user selects an item in the master list box:

<Page
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
  <Page.Resources>
    <XmlDataProvider x:Key="Programs">
      <x:XData>
        <Programs xmlns="">
          <Program name="Some program">
            <Step name="Some program step 1"/>
            <Step name="Some program step 2"/>
            <Step name="Some program step 3"/>
            <Step name="Some program step 4"/>
          </Program>
          <Program name="Some other program">
            <Step name="Some other program step 1"/>
            <Step name="Some other program step 2"/>
            <Step name="Some other program step 3"/>
            <Step name="Some other program step 4"/>
          </Program>        
        </Programs>
      </x:XData>
    </XmlDataProvider>
  </Page.Resources>
  <DockPanel>  
    <Label DockPanel.Dock="Top">Programs</Label>
    <ListBox x:Name="Program" DockPanel.Dock="Top" ItemsSource="{Binding Source={StaticResource Programs}, XPath=/Programs/Program}">
      <ListBox.ItemTemplate>
        <DataTemplate>
          <TextBlock Text="{Binding XPath=@name}"/>
        </DataTemplate>
      </ListBox.ItemTemplate>
    </ListBox>
    <Label DockPanel.Dock="Top">Steps</Label>
    <ListBox x:Name="Step" DockPanel.Dock="Top" DataContext="{Binding ElementName=Program, Path=SelectedItem}" ItemsSource="{Binding XPath=Step/@name}"/>
  </DockPanel>
</Page>

What has to change in order for the detail to change only when the user clicks a button? One thing: the DataContext on the ListBox named Step. You need to use code-behind to do this, but the code is pretty simple:

private void Button_Click(object sender, RoutedEventArgs e)
{
    if (Program.SelectedItem != null)
    {
        Step.DataContext = Program.SelectedItem;
    }
}

Edit

In order for the above to work, you have to change the Step ListBox to:

<ListBox x:Name="Step" DockPanel.Dock="Top" ItemsSource="{Binding XPath=Step/@name}"/>

That ListBox won’t display anything unless its DataContext is assigned.