为什么不是'；我的ViewModel中的某个属性在DataGrid更改时更新

我正在尝试创建一个UserControl，它将允许我在网格中编辑Dictionary<string,string>类型的Dictionary（到目前为止只是编辑条目，而不是添加或删除）。

每当我将DataGrid绑定到Dictionary时，它都会将网格显示为只读，因此我决定创建一个值转换器，将其转换为ObservableCollection<DictionaryEntry>，其中DictionaryEntry只是一个具有两个属性Key和Value的类。

这适用于在网格中显示字典，但现在当我对网格进行更改时，我的字典不会更新。我不确定为什么。

我认为这要么是我设置绑定的方式有问题，要么是我的值转换器有问题。如果有人能透露一些信息，那就太棒了。

下面是我能做的最小的演示，展示了我在做什么。同样的问题是，当我更改网格中的值时，MainViewModel上的MyDictionary不会更新。。曾经为什么？

MainViewModel.cs

public class MainViewModel : INotifyPropertyChanged
{
    public MainViewModel()
    {
        _myDictionary = new Dictionary<string, string>()
            {
                {"Key1", "Value1"},
                {"Key2", "Value2"},
                {"Key3", "Value3"}
            };
    }
    private Dictionary<string, string> _myDictionary;
    public Dictionary<string, string> MyDictionary
    {
        get
        {
            return _myDictionary;
        }
        set
        {
            if (_myDictionary == value)
                return;
            _myDictionary = value;
            OnPropertyChanged("MyDictionary");
        }
    }
...
}

主窗口.xaml

<Window ...>
    <Window.Resources>
        <local:MainViewModel x:Key="MainViewModel"></local:MainViewModel>
    </Window.Resources>
    <StackPanel Name="MainStackPanel" DataContext="{Binding Source={StaticResource MainViewModel}}">
        <local:DictionaryGrid />
        <Button Content="Print Dictionary" Click="PrintDictionary"></Button>        
    </StackPanel>
</Window>

DictionaryGrid.xaml

<UserControl ...>
      <UserControl.Resources>
         <testingGrid:DictionaryToOcConverter x:Key="Converter" />
     </UserControl.Resources>
    <Grid>
        <DataGrid ItemsSource="{Binding MyDictionary, 
                                  Converter={StaticResource Converter}}" 
         />
    </Grid>
</UserControl>

DictionaryToOcConverter.cs

public class DictionaryToOcConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var collection = new ObservableCollection<DictionaryEntry>();
        var dictionary = value as Dictionary<string, string>;
        if (dictionary != null)
        {
            foreach (var kvp in dictionary)
                collection.Add(new DictionaryEntry { Key = kvp.Key, Value = kvp.Value });
        }
        return collection;
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        var dictionary = new Dictionary<string, string>();
        var entries = value as ObservableCollection<DictionaryEntry>;
        if (entries != null)
        {
            foreach (var entry in entries)
                dictionary.Add(entry.Key, entry.Value);
        }
        return dictionary;
    }
    public class DictionaryEntry
    {
        public string Key { get; set; }
        public string Value { get; set; }
    }
}

public class DictionaryEntry : INotifyPropertyChanged, IEditableObject
{
    private string _k;
    [Description("The key")]
    public string K
    {
        [DebuggerStepThrough]
        get { return _k; }
        [DebuggerStepThrough]
        set
        {
            if (value != _k)
            {
                _k = value;
                OnPropertyChanged("K");
            }
        }
    }
    private string _v;
    [Description("The value")]
    public string V
    {
        [DebuggerStepThrough]
        get { return _v; }
        [DebuggerStepThrough]
        set
        {
            if (value != _v)
            {
                _v = value;
                OnPropertyChanged("V");
            }
        }
    }
    #region INotifyPropertyChanged Implementation
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string name)
    {
        var handler = System.Threading.Interlocked.CompareExchange(ref PropertyChanged, null, null);
        if (handler != null)
        {
            handler(this, new PropertyChangedEventArgs(name));
        }
    }
    #endregion
    #region IEditableObject
    public void BeginEdit()
    {
        // implementation goes here
    }
    public void CancelEdit()
    {
        // implementation goes here
    }
    public void EndEdit()
    {
        // implementation goes here
    }
    #endregion
}

    public ObservableCollection<DictionaryEntry> MyItems { get; set; } 
    public ViewModel()
    {
        MyItems = new ObservableCollection<DictionaryEntry>();
        MyItems.Add(new DictionaryEntry{K="string1", V="value1"});
        MyItems.Add(new DictionaryEntry { K = "color", V = "red" });
    }

    <DataGrid ItemsSource="{Binding MyItems}" AutoGenerateColumns="True">
    </DataGrid>