C# – WPF Binding to parent DataContext

bindingcwpf

We have a WPF application with a standard MVVM pattern, leveraging Cinch (and therefore MefedMVVM) for View -> ViewModel resolution. This works well, and I can bind the relevant controls to properties on the ViewModel.

Within a particular View, we have an Infragistics XamGrid. This grid is bound to an ObservableCollection on the ViewModel, and displays the appropriate rows. However, I then have a specific column on this grid which I am trying to bind a TextBox text value to a property on the parent DataContext, rather than the ObservableCollection. This binding is failing.

We've gone through several options here including:

Using AncestorType to track up the tree and bind to the DataContext of the parent UserControl like so (from the great answer to this question, as well as this one)…
```
{Binding Path=PathToProperty, RelativeSource={RelativeSource AncestorType={x:Type typeOfAncestor}}}
```
Specifying the ElementName and trying to target the top level control directly. Have a look here if you'd like to read about using ElementName.
Using a 'proxy' FrameorkElement defined in the resources for the UserControl to try and 'pass in' the context as required. We define the element as below, then reference as a static resource…
```
<FrameworkElement x:Key="ProxyContext" DataContext="{Binding Path=DataContext, RelativeSource={RelativeSource Self}}"></FrameworkElement>
```

In this case the binding finds the FrameworkElement, but can not access anything beyond that (when specifying a Path).

Having read around, it looks quite likely that this is caused by the Infragistics XamGrid building columns outside of the tree. However, even if this is the case, at least options 2 or 3 should work.

Our last thoughts are that it is related to the V – VM binding, but even using Snoop we've yet to find what the exact issue is. I'm by no means an expert with WPF binding so any pointers would be appreciated.

EDIT: I have found some templating examples from Infragistics here that I will try.

EDIT 2: As pointed out by @Dtex, templates are the way to go. Here is the relevant snippet for use with a XamGrid:

<ig:GroupColumn Key="CurrentDate">
                <ig:GroupColumn.HeaderTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Path=DataContext.CurrentDateTest, RelativeSource={RelativeSource AncestorType=UserControl}}" />
                    </DataTemplate>
                </ig:GroupColumn.HeaderTemplate>
                <ig:GroupColumn.Columns>

I've left the XML open… you'd simply add the columns you wanted, then close off the relevant tags.

Best Answer

I dont know about XamGrid but that's what i'll do with a standard wpf DataGrid:

<DataGrid>
    <DataGrid.Columns>
        <DataGridTemplateColumn>
            <DataGridTemplateColumn.CellTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding DataContext.MyProperty, RelativeSource={RelativeSource AncestorType=MyUserControl}}"/>
                </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
            <DataGridTemplateColumn.CellEditingTemplate>
                <DataTemplate>
                    <TextBox Text="{Binding DataContext.MyProperty, RelativeSource={RelativeSource AncestorType=MyUserControl}}"/>
                </DataTemplate>
            </DataGridTemplateColumn.CellEditingTemplate>
        </DataGridTemplateColumn>
    </DataGrid.Columns>
</DataGrid>

Since the TextBlock and the TextBox specified in the cell templates will be part of the visual tree, you can walk up and find whatever control you need.

Related Solutions

C# – Binding a WPF ComboBox to a custom list

You set the DisplayMemberPath and the SelectedValuePath to "Name", so I assume that you have a class PhoneBookEntry with a public property Name.

Have you set the DataContext to your ConnectionViewModel object?

I copied you code and made some minor modifications, and it seems to work fine. I can set the viewmodels PhoneBookEnty property and the selected item in the combobox changes, and I can change the selected item in the combobox and the view models PhoneBookEntry property is set correctly.

Here is my XAML content:

<Window x:Class="WpfApplication6.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="300" Width="300">
<Grid>
    <StackPanel>
        <Button Click="Button_Click">asdf</Button>
        <ComboBox ItemsSource="{Binding Path=PhonebookEntries}"
                  DisplayMemberPath="Name"
                  SelectedValuePath="Name"
                  SelectedValue="{Binding Path=PhonebookEntry}" />
    </StackPanel>
</Grid>
</Window>

And here is my code-behind:

namespace WpfApplication6
{

    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
            ConnectionViewModel vm = new ConnectionViewModel();
            DataContext = vm;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ((ConnectionViewModel)DataContext).PhonebookEntry = "test";
        }
    }

    public class PhoneBookEntry
    {
        public string Name { get; set; }

        public PhoneBookEntry(string name)
        {
            Name = name;
        }

        public override string ToString()
        {
            return Name;
        }
    }

    public class ConnectionViewModel : INotifyPropertyChanged
    {
        public ConnectionViewModel()
        {
            IList<PhoneBookEntry> list = new List<PhoneBookEntry>();
            list.Add(new PhoneBookEntry("test"));
            list.Add(new PhoneBookEntry("test2"));
            _phonebookEntries = new CollectionView(list);
        }

        private readonly CollectionView _phonebookEntries;
        private string _phonebookEntry;

        public CollectionView PhonebookEntries
        {
            get { return _phonebookEntries; }
        }

        public string PhonebookEntry
        {
            get { return _phonebookEntry; }
            set
            {
                if (_phonebookEntry == value) return;
                _phonebookEntry = value;
                OnPropertyChanged("PhonebookEntry");
            }
        }

        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
        public event PropertyChangedEventHandler PropertyChanged;
    }
}

Edit: Geoffs second example does not seem to work, which seems a bit odd to me. If I change the PhonebookEntries property on the ConnectionViewModel to be of type ReadOnlyCollection, the TwoWay binding of the SelectedValue property on the combobox works fine.

Maybe there is an issue with the CollectionView? I noticed a warning in the output console:

System.Windows.Data Warning: 50 : Using CollectionView directly is not fully supported. The basic features work, although with some inefficiencies, but advanced features may encounter known bugs. Consider using a derived class to avoid these problems.

Edit2 (.NET 4.5): The content of the DropDownList can be based on ToString() and not of DisplayMemberPath, while DisplayMemberPath specifies the member for the selected and displayed item only.

C# – Using the parent’s DataContext (WPF – Dynamic Menu Command Binding)

Use the binding below for your button's command:

{Binding DataContext.CommandName, 
         RelativeSource={RelativeSource FindAncestor, 
                         AncestorType={x:Type MyUserControl}}}

This will tell it to find your UserControl and use its DataContext.

Best Answer

Related Solutions

C# – Binding a WPF ComboBox to a custom list

C# – Using the parent’s DataContext (WPF – Dynamic Menu Command Binding)

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