WPF 将 DataGrid 组合框选定项绑定到选定 DataGridRow 的数据上下文

Question

我有一个绑定到单独 ItemsSource 的 DataGridTemplateColumn 组合框似乎通过将此组合框绑定到另一个源它会更改 DataContext。

所以我在将组合框中所选项目的值绑定到 DataGrid 中所选行的 DataContext 时遇到问题。

XAML：

<DataGrid HorizontalAlignment="Left"  ItemsSource="{Binding Path=WorldDataList}"  SelectedItem="{Binding SelectedWorldData}">           
    <DataGridTemplateColumn Header="Country" >
        <DataGridTemplateColumn.CellTemplate >
            <DataTemplate>
                <ComboBox ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type StackPanel}},Path=DataContext.Countries}" 
                          SelectedItem="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGrid}}, Path=SelectedItem.Country}" 
                          SelectedIndex="0"/>  
            </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
    </DataGridTemplateColumn>
</DataGrid>

C#：

class WorldDataViewModel : ObservableObject
{
    private ObservableCollection<WorldData> _worldDataList = new ObservableCollection<WorldData>();
    public ObservableCollection<WorldData> WorldDataList
    {
        get { return _worldDataList; }
        set
        {
            Set(ref _worldDataList, value);
        }
    }

    public List<string> Countries {get;set;}

    private WorldData worldData;
    private WorldData SelectedWorldData
    {
        get{return worldData;}
        set
        {
            Set(ref worldData, value);
        }
    }
}

class WorldData : ObservableObject
{
    private string country;
    public string Country
    {
        get{return country;} 
        set
        {
            Set(ref country, value);
        }  
}

我得到了例外：

System.Windows.Data 错误：23：无法转换“{NewItemPlaceholder}” 从“NamedObject”类型到“en-US”文化类型“WorldData” 默认转换；考虑使用 Binding 的 Converter 属性。 NotSupportedException:'System.NotSupportedException: TypeConverter 无法从 MS.Internal.NamedObject 转换。在 System.ComponentModel.TypeConverter.GetConvertFromException（对象 值）在 System.ComponentModel.TypeConverter.ConvertFrom(ITypeDescriptorContext 上下文，CultureInfo 文化，对象值）在 MS.Internal.Data.DefaultValueConverter.ConvertHelper（对象 o，类型 destinationType、DependencyObject targetElement、CultureInfo 文化、 Boolean isForward)' 抛出异常：'System.NotSupportedException' 在 PresentationFramework.dll 中

似乎我应该使用类型转换器，但似乎我不应该这样做，因为我在 SO 上找到的很少

我想现在我将放弃并为组合框添加一个单独的框并绑定到 Datagrid 的选定项。我不觉得它很直观，所以如果你有任何聪明的想法，请。

Answer 1

这是我的完整测试应用程序，它将所选国家/地区保存回WorldData 视图模型。没有UpdateSourceTrigger 上的SelectedItem，它不起作用。

<Window
    x:Class="ComboboxInDataGrid.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    Title="MainWindow"
    Width="525"
    Height="350"
    mc:Ignorable="d">
    <Grid>
        <DataGrid x:Name="me"
            HorizontalAlignment="Left"
            AutoGenerateColumns="False"
            CanUserAddRows="False"
            ItemsSource="{Binding Path=WorldDataList}"
            SelectedItem="{Binding SelectedWorldData}">
            <DataGrid.Columns>
                <DataGridTemplateColumn Header="Country">
                    <DataGridTemplateColumn.CellTemplate>
                        <DataTemplate>
                            <Grid>
                                <ComboBox ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, 
                                                                                               AncestorType={x:Type DataGrid}},
                                                                Path=DataContext.Countries}"
                                          SelectedItem="{Binding Path=Country, 
                                                                 Mode=TwoWay,
                                                                 UpdateSourceTrigger=PropertyChanged}" />
                            </Grid>
                        </DataTemplate>
                    </DataGridTemplateColumn.CellTemplate>
                </DataGridTemplateColumn>
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>


using System.Collections.Generic;
using System.Windows;

namespace ComboboxInDataGrid
{
    public partial class MainWindow : Window
    {
        public MainWindow ()
        {
            DataContext = new WorldDataViewModel ();
            InitializeComponent ();
        }
    }

    class WorldDataViewModel
    {
        public WorldDataViewModel ()
        {
            var c1 = "USA";
            var c2 = "Canada";
            var c3 = "Brasil";
            var c4 = "Brasfsdfsil";

            Countries = new List<string> ();
            Countries.Add (c1);
            Countries.Add (c2);
            Countries.Add (c3);
            Countries.Add (c4);

            _worldDataList.Add (new WorldData { Index = 1, Country = c2 });
            _worldDataList.Add (new WorldData { Index = 2, Country = c3 });
            _worldDataList.Add (new WorldData { Index = 3, Country = c4 });
        }

        private List<WorldData> _worldDataList = new List<WorldData> ();
        public List<WorldData> WorldDataList
        {
            get
            {
                return _worldDataList;
            }
            set
            {
                _worldDataList = value;

            }
        }

        public List<string> Countries { get; set; }

        private WorldData worldData;
        public WorldData SelectedWorldData
        {
            get
            {
                return worldData;
            }

            set
            {
                worldData = value;
            }
        }
    }

    public class WorldData
    {
        public int Index { get; set; }

        private string country;
        public string Country
        {
            get { return country; }
            set
            {
                country = value;
            }
        }
    }
}