Binding ItemsSource of a ComboBoxColumn in WPF Dat

Question

I have two simple Model classes and a ViewModel...

public class GridItem
{
    public string Name { get; set; }
    public int CompanyID { get; set; }
}

public class CompanyItem
{
    public int ID { get; set; }
    public string Name { get; set; }
}

public class ViewModel
{
    public ViewModel()
    {
        GridItems = new ObservableCollection<GridItem>() {
            new GridItem() { Name = "Jim", CompanyID = 1 } };

        CompanyItems = new ObservableCollection<CompanyItem>() {
            new CompanyItem() { ID = 1, Name = "Company 1" },
            new CompanyItem() { ID = 2, Name = "Company 2" } };
    }

    public ObservableCollection<GridItem> GridItems { get; set; }
    public ObservableCollection<CompanyItem> CompanyItems { get; set; }
}

...and a simple Window:

<Window x:Class="DataGridComboBoxColumnApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <DataGrid AutoGenerateColumns="False" ItemsSource="{Binding GridItems}" >
            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding Name}" />
                <DataGridComboBoxColumn ItemsSource="{Binding CompanyItems}"
                                    DisplayMemberPath="Name"
                                    SelectedValuePath="ID"
                                    SelectedValueBinding="{Binding CompanyID}" />
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>

The ViewModel is set to the MainWindow's DataContext in App.xaml.cs:

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        base.OnStartup(e);

        MainWindow window = new MainWindow();
        ViewModel viewModel = new ViewModel();

        window.DataContext = viewModel;
        window.Show();
    }
}

As you can see I set the ItemsSource of the DataGrid to the GridItems collection of the ViewModel. This part works, the single Grid line with Name "Jim" is displayed.

I also want to set the ItemsSource of the ComboBox in every row to the CompanyItems collection of the ViewModel. This part does not work: The ComboBox remains empty and in the Debugger Output Window I see an error message:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=CompanyItems; DataItem=null; target element is 'DataGridComboBoxColumn' (HashCode=28633162); target property is 'ItemsSource' (type 'IEnumerable')

I believe that WPF expects CompanyItems to be a property of GridItem which is not the case, and that's the reason why the binding fails.

I've already tried to work with a RelativeSource and AncestorType like so:

<DataGridComboBoxColumn ItemsSource="{Binding CompanyItems, 
    RelativeSource={RelativeSource Mode=FindAncestor,
                                   AncestorType={x:Type Window}}}"
                        DisplayMemberPath="Name"
                        SelectedValuePath="ID"
                        SelectedValueBinding="{Binding CompanyID}" />

But that gives me another error in the debugger output:

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Window', AncestorLevel='1''. BindingExpression:Path=CompanyItems; DataItem=null; target element is 'DataGridComboBoxColumn' (HashCode=1150788); target property is 'ItemsSource' (type 'IEnumerable')

Question: How can I bind the ItemsSource of the DataGridComboBoxColumn to the CompanyItems collection of the ViewModel? Is it possible at all?

Thank you for help in advance!

Answer 1

The correct solution seems to be:

<Window.Resources>
    <CollectionViewSource x:Key="ItemsCVS" Source="{Binding MyItems}" />
</Window.Resources>
<!-- ... -->
<DataGrid ItemsSource="{Binding MyRecords}">
    <DataGridComboBoxColumn Header="Column With Predefined Values"
                            ItemsSource="{Binding Source={StaticResource ItemsCVS}}"
                            SelectedValueBinding="{Binding MyItemId}"
                            SelectedValuePath="Id"
                            DisplayMemberPath="StatusCode" />
</DataGrid>

The layout above works perfectly fine for me, and should work for others. This design choice also makes sense, though it isn't very well explained anywhere. But if you have a data column with predefined values, those values typically don't change during run-time. So creating a CollectionViewSource and initializing the data once makes sense. It also gets rid of the longer bindings to find an ancestor and bind on it's data context (which always felt wrong to me).

I am leaving this here for anyone else who struggled with this binding, and wondered if there was a better way (As this page is obviously still coming up in search results, that's how I got here).

Answer 2

the bast way i use i bind the textblock and combobox to same property and this property should support notifyPropertyChanged.

i used relativeresource to bind to parent view datacontext which is usercontrol to go up datagrid level in binding because in this case the datagrid will search in object that you used in datagrid.itemsource

<DataGridTemplateColumn Header="your_columnName">
     <DataGridTemplateColumn.CellTemplate>
          <DataTemplate>
             <TextBlock Text="{Binding RelativeSource={RelativeSource AncestorType={x:Type UserControl}}, Path=DataContext.SelectedUnit.Name, Mode=TwoWay}" />
           </DataTemplate>
     </DataGridTemplateColumn.CellTemplate>
     <DataGridTemplateColumn.CellEditingTemplate>
           <DataTemplate>
            <ComboBox DisplayMemberPath="Name"
                      IsEditable="True"
                      ItemsSource="{Binding RelativeSource={RelativeSource AncestorType={x:Type UserControl}}, Path=DataContext.UnitLookupCollection}"
                       SelectedItem="{Binding RelativeSource={RelativeSource AncestorType={x:Type UserControl}}, Path=DataContext.SelectedUnit, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                      SelectedValue="{Binding UnitId, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                      SelectedValuePath="Id" />
            </DataTemplate>
    </DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>

Answer 3

Pls, check if DataGridComboBoxColumn xaml below would work for you:

<DataGridComboBoxColumn 
    SelectedValueBinding="{Binding CompanyID}" 
    DisplayMemberPath="Name" 
    SelectedValuePath="ID">

    <DataGridComboBoxColumn.ElementStyle>
        <Style TargetType="{x:Type ComboBox}">
            <Setter Property="ItemsSource" Value="{Binding Path=DataContext.CompanyItems, RelativeSource={RelativeSource AncestorType={x:Type Window}}}" />
        </Style>
    </DataGridComboBoxColumn.ElementStyle>
    <DataGridComboBoxColumn.EditingElementStyle>
        <Style TargetType="{x:Type ComboBox}">
            <Setter Property="ItemsSource" Value="{Binding Path=DataContext.CompanyItems, RelativeSource={RelativeSource AncestorType={x:Type Window}}}" />
        </Style>
    </DataGridComboBoxColumn.EditingElementStyle>
</DataGridComboBoxColumn>

Here you can find another solution for the problem you're facing: Using combo boxes with the WPF DataGrid

Answer 4

RookieRick is right, using DataGridTemplateColumn instead of DataGridComboBoxColumn gives a much simpler XAML.

Moreover, putting the CompanyItem list directly accessible from the GridItem allows you to get rid of the RelativeSource.

IMHO, this give you a very clean solution.

XAML:

<DataGrid AutoGenerateColumns="False" ItemsSource="{Binding GridItems}" >
    <DataGrid.Resources>
        <DataTemplate x:Key="CompanyDisplayTemplate" DataType="vm:GridItem">
            <TextBlock Text="{Binding Company}" />
        </DataTemplate>
        <DataTemplate x:Key="CompanyEditingTemplate" DataType="vm:GridItem">
            <ComboBox SelectedItem="{Binding Company}" ItemsSource="{Binding CompanyList}" />
        </DataTemplate>
    </DataGrid.Resources>
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding Name}" />
        <DataGridTemplateColumn CellTemplate="{StaticResource CompanyDisplayTemplate}"
                                CellEditingTemplate="{StaticResource CompanyEditingTemplate}" />
    </DataGrid.Columns>
</DataGrid>

View model:

public class GridItem
{
    public string Name { get; set; }
    public CompanyItem Company { get; set; }
    public IEnumerable<CompanyItem> CompanyList { get; set; }
}

public class CompanyItem
{
    public int ID { get; set; }
    public string Name { get; set; }

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

public class ViewModel
{
    readonly ObservableCollection<CompanyItem> companies;

    public ViewModel()
    {
        companies = new ObservableCollection<CompanyItem>{
            new CompanyItem { ID = 1, Name = "Company 1" },
            new CompanyItem { ID = 2, Name = "Company 2" }
        };

        GridItems = new ObservableCollection<GridItem> {
            new GridItem { Name = "Jim", Company = companies[0], CompanyList = companies}
        };
    }

    public ObservableCollection<GridItem> GridItems { get; set; }
}

Answer 5

Your ComboBox is trying to bind to bind to GridItem[x].CompanyItems, which doesn't exist.

Your RelativeBinding is close, however it needs to bind to DataContext.CompanyItems because Window.CompanyItems does not exist

Answer 6

The documentation on MSDN about the ItemsSource of the DataGridComboBoxColumn says that only static resources, static code or inline collections of combobox items can be bound to the ItemsSource:

To populate the drop-down list, first set the ItemsSource property for the ComboBox by using one of the following options:

• A static resource. For more information, see StaticResource Markup Extension.
• An x:Static code entity. For more information, see x:Static Markup Extension.
• An inline collection of ComboBoxItem types.

Binding to a DataContext's property is not possible if I understand that correctly.

And indeed: When I make CompanyItems a static property in ViewModel ...

public static ObservableCollection<CompanyItem> CompanyItems { get; set; }

... add the namespace where the ViewModel is located to the window ...

xmlns:vm="clr-namespace:DataGridComboBoxColumnApp"

... and change the binding to ...

<DataGridComboBoxColumn
    ItemsSource="{Binding Source={x:Static vm:ViewModel.CompanyItems}}" 
    DisplayMemberPath="Name"
    SelectedValuePath="ID"
    SelectedValueBinding="{Binding CompanyID}" />

... then it works. But having the ItemsSource as a static property might be sometimes OK, but it is not always what I want.