MVVM Data Binding Datagrid with Combobox / 不同的itemssource

Question

我有一个用于用户输入的数据网格，每个单元格都是一个用于数据选择的组合框。选定的值应绑定到数据网格的 itemsource 以便稍后将数据保存到我的数据库中。组合框值应来自不同的 itemsource。

用户界面：

                    <DataGrid ItemsSource="{Binding Users}">
                        <DataGrid.Columns>
                             <DataGridTemplateColumn Header="Firstname">
                                <DataGridTemplateColumn.CellTemplate>
                                    <HierarchicalDataTemplate>
                                        <ComboBox ItemsSource="{Binding Firstnames}" DisplayMemberPath="Name"/>
                                    </HierarchicalDataTemplate>
                                </DataGridTemplateColumn.CellTemplate>
                            </DataGridTemplateColumn>
                        </DataGrid.Columns>
                    </DataGrid>
                    <ComboBox ItemsSource="{Binding Firstnames}" DisplayMemberPath="Name">

                    </ComboBox>
                </StackPanel>

模型和视图模型：

// Models

public class User 
{
    public string Firstname { get; set; }
    public string Lastname {get; set; }
}

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

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


//ViewModel

public class GenerateViewModel : NotifyUIBase
{

    #region properties
    public ObservableCollection<User> Users { get; set; }

    public ObservableCollection<Firstname> Firstnames { get; set; }
    public ObservableCollection<Lastname> Lastnames { get; set; }

    #endregion


    #region Constructor

    public GenerateViewModel()

    {
        Firstnames = new ObservableCollection<Firstname>()
        {
            new Firstname() {Name="Firstname1"},
            new Firstname() {Name= "Firstname2"}
        };
        Lastnames = new ObservableCollection<Lastname>()
        {
            new Lastname() {Name="Lastname1"},
            new Lastname() {Name= "Lastname2"}
        };
        Users = new ObservableCollection<User> {new User()};

    }

    #endregion

    #region Methods


    #endregion


}

数据网格内部的组合框保持为空，但我与数据网格外部的附加组合框的绑定效果很好。

Answer 1

DataContext 无法识别，必须从主窗口获取：

 <HierarchicalDataTemplate>
         <ComboBox ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, 
                                         AncestorType={x:Type Window}}, 
                                         Path=DataContext.Firstnames}" 
                   DisplayMemberPath="Name"/>
 </HierarchicalDataTemplate>