无法对TextBox执行同等的文本绑定

在我的程序中，我有一个绑定到数据模型中的属性值的TextBlock。我想将这个TextBlock更改为TextBox，以便它是可编辑的，但仍然想将文本绑定到它。问题是，当我将TextBlock更改为TextBox时，我的绑定不起作用，TextBox显示空白。

我要绑定到的属性是程序中已有的自定义类的属性。

这是属性:

//Property for Display Name
public MultiItemString DisplayName {}

这是MultiItemString类:

public class MultiItemString : INotifyPropertyChanged
{
    private readonly string[] _keys;
    private readonly MultiItemString[] _nestedItems;
    readonly bool _resourceKey;
    private readonly bool _nestedMultiItemStrings;
    public MultiItemString(IEnumerable<string> keys, bool resourceKey = true)
    {
        _keys = keys.ToArray();
        _resourceKey = resourceKey;
        LanguageChange.LanguageChagned += (sender, args) => RaisePropertyChanged("");
    }
    public MultiItemString(IEnumerable<MultiItemString> nestedItems)
    {
        _nestedItems = nestedItems.ToArray();
        foreach (var multiItemString in _nestedItems)
        {
            multiItemString.PropertyChanged += (s, e) => RaisePropertyChanged("Value");
        }
        _nestedMultiItemStrings = true;
    }
    public string Key
    {
        get
        {
            if (_keys != null && _keys.Length != 0) return _keys[0];
            return null;
        }
    }
    public string Value
    {
        get
        {
            var sb = new StringBuilder();
            if (_nestedMultiItemStrings)
            {
                foreach (var MultiItemString in _nestedItems)
                {
                    sb.Append(MultiItemString.Value);
                }
            }
            else
            {
                foreach (var key in _keys)
                {
                    sb.Append(_resourceKey ? (string)Application.Current.Resources[key] : key);
                }
            }
            return sb.ToString();
        }
    }
    public override string ToString()
    {
        return Value;
    }
    public event PropertyChangedEventHandler PropertyChanged;
    void RaisePropertyChanged(string propertyName)
    {
        var temp = PropertyChanged;
        if (temp != null)
            temp(this, new PropertyChangedEventArgs(propertyName));
    }
}

我的xaml

:

<TextBox Text="{Binding Model.DisplayName}" Height="28" HorizontalAlignment="Left" Name="title_TB" VerticalAlignment="Top" Width="Auto" FontWeight="Bold" FontSize="14" Margin="5,2,0,0" />

如何将此属性绑定到TextBox作为文本值，就像我对TextBlock一样?

<TextBox Text="{Binding Model.DisplayName.Value}" Height="28" HorizontalAlignment="Left" Name="title_TB" VerticalAlignment="Top" Width="Auto" FontWeight="Bold" FontSize="14" Margin="5,2,0,0" />

private string _thisShouldBeAValidField ;
    public string Value
        {
            get
            {
if(_thisShouldBeAValidField!=null) return _thisShouldBeAValidField;
                var sb = new StringBuilder();
                if (_nestedMultiItemStrings)
                {
                    foreach (var MultiItemString in _nestedItems)
                    {
                        sb.Append(MultiItemString.Value);
                    }
                }
                else
                {
                    foreach (var key in _keys)
                    {
                        sb.Append(_resourceKey ? (string)Application.Current.Resources[key] : key);
                    }
                }
                return sb.ToString();
            }
    set{
    _thisShouldBeAValidField = value;
    }
        }