WPF 如何创建具有验证和绑定的自定义文本框

我正在开发一个用于货币编辑的自定义文本框。
我见过一些现成的，但它们很复杂和/或并不真正可用，迫使您采取不良做法（例如对应该在控件上使用的名称进行硬编码）。
因此，我决定自己完成此操作，但在使用绑定选项时遇到了麻烦，因为分配给绑定属性的属性必须是小数，但 TextBox 控件的 Text 属性接受字符串。
我想的答案是，也许可以重写基类（TextBox）中 Text 属性的访问方法（getter 和 setter），但这是不允许的。
我的绑定应该设置为值，该值将 TextBox 的文本属性设置为文本（带有货币符号和所有内容），但在 Get 方法上将其转换回数字数据类型。
这是我到目前为止所取得的成就：

public class CurrencyTextBox : TextBox
    {
        private bool IsValidKey(Key key)
        {
            int k = (int)key;
            return ((k >= 34 && k <= 43) //digits 0 to 9
                || (k >= 74 && k <= 83) //numeric keypad 0 to 9
                || (k == 2) //back space
                || (k == 32) //delete
                );
        }
        private void Format()
        {
            //formatting decimal to currency text here
            //Done! no problems here
        }
        private void FormatBack()
        {
            //formatting currency text to decimal here
            //Done! no problems here
        }
        private void ValueChanged(object sender, TextChangedEventArgs e)
        {
            this.Format();
        }
        private void MouseClicked(object sender, MouseButtonEventArgs e)
        {
            this.Format();
            // Prevent changing the caret index
            this.CaretIndex = this.Text.Length;
            e.Handled = true;
        }
        private void MouseReleased(object sender, MouseButtonEventArgs e)
        {
            this.Format();
            // Prevent changing the caret index
            this.CaretIndex = this.Text.Length;
            e.Handled = true;
        }
        private void KeyPressed(object sender, KeyEventArgs e)
        {
            if (IsValidKey(e.Key))
                e.Handled = true;
            if (Keyboard.Modifiers != ModifierKeys.None)
                return;
            this.Format();
        }
        private void PastingEventHandler(object sender, DataObjectEventArgs e)
        {
            // Prevent copy/paste
            e.CancelCommand();
        }
        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
            // Disable copy/paste
            DataObject.AddCopyingHandler(this, PastingEventHandler);
            DataObject.AddPastingHandler(this, PastingEventHandler);
            this.CaretIndex = this.Text.Length;
            this.PreviewKeyUp += KeyPressed;
            this.PreviewMouseDown += MouseClicked;
            this.PreviewMouseUp += MouseReleased;
            this.TextChanged += ValueChanged;
            this.Format();
        }
    }

这是 XAML：

<MyNamespace:CurrencyTextBox x:Name="TxbCurrency" Text="{Binding Path=DataContext.Element.Currency, ValidatesOnDataErrors=True}" />

到目前为止，一切都很好！从小数属性到 TextBox 文本的绑定是“正确的”。但如何在编辑后的文本中取回小数点是现在的问题。
从十进制到 .Text 的绑定使用装箱来隐藏 ToString() 方法。
问题在这里：在这种情况下，如何从十进制重载 Parse() 方法以使用 FormatBack() 方法从 TextBox 的文本中获取小数？

好吧，为了将来的目的，如果有人遇到同样的麻烦，这里是货币文本框的完整代码。随意使用它、修改它、出售它（你不要认为它有价值），或者随心所欲地使用它！

/*
 * the necessary usings:
 * using System.Globalization;
 * using System.Windows;
 * using System.Windows.Controls;
 * using System.Windows.Input;
 * using System.Threading;
 * And don't forget to change the currency settings on the XAML
 * or in the defaults (on the contructor)
 * It's set by default to Brazilian Real (R$)
 */
public class CurrencyTextBox : TextBox
{
    public CurrencyTextBox()
    {
        CurrencySymbol = "R$ ";
        CurrencyDecimalPlaces = 2;
        DecimalSeparator = ",";
        ThousandSeparator = ".";
        Culture = "pt-BR";
    }
    public string CurrencySymbol { get; set; }
    private int CurrencyDecimalPlaces { get; set; }
    public string DecimalSeparator { get; set; }
    public string ThousandSeparator { get; set; }
    public string Culture { get; set; }
    private bool IsValidKey(int k)
    {
        return (k >= 34 && k <= 43) //digits 0 to 9
            || (k >= 74 && k <= 83) //numeric keypad 0 to 9
            || (k == 2) //back space
            || (k == 32) //delete
            ;
    }
    private string Format(string text)
    {
        string unformatedString = text == string.Empty ? "0,00" : text; //Initial state is always string.empty
        unformatedString = unformatedString.Replace(CurrencySymbol, ""); //Remove currency symbol from text
        unformatedString = unformatedString.Replace(DecimalSeparator, ""); //Remove separators (decimal)
        unformatedString = unformatedString.Replace(ThousandSeparator, ""); //Remove separators (thousands)
        decimal number = decimal.Parse(unformatedString) / (decimal)Math.Pow(10, CurrencyDecimalPlaces); //The value will have 'x' decimal places, so divide it by 10^x
        unformatedString = number.ToString("C", CultureInfo.CreateSpecificCulture(Culture));
        return unformatedString;
    }
    private decimal FormatBack(string text)
    {
        string unformatedString = text == string.Empty ? "0.00" : text;
        unformatedString = unformatedString.Replace(CurrencySymbol, ""); //Remove currency symbol from text
        unformatedString = unformatedString.Replace(ThousandSeparator, ""); //Remove separators (thousands);
        CultureInfo current = Thread.CurrentThread.CurrentUICulture; //Let's change the culture to avoid "Input string was in an incorrect format"
        Thread.CurrentThread.CurrentUICulture = CultureInfo.CreateSpecificCulture(Culture);
        decimal returnValue = decimal.Parse(unformatedString);
        Thread.CurrentThread.CurrentUICulture = current; //And now change it back, cuz we don't own the world, right?
        return returnValue;
    }
    private void ValueChanged(object sender, TextChangedEventArgs e)
    {
        // Keep the caret at the end
        this.CaretIndex = this.Text.Length;
    }
    private void MouseClicked(object sender, MouseButtonEventArgs e)
    {
        // Prevent changing the caret index
        e.Handled = true;
        this.Focus();
    }
    private void MouseReleased(object sender, MouseButtonEventArgs e)
    {
        // Prevent changing the caret index
        e.Handled = true;
        this.Focus();
    }
    private void KeyReleased(object sender, KeyEventArgs e)
    {
        this.Text = Format(this.Text);
        this.Value = FormatBack(this.Text);
    }
    private void KeyPressed(object sender, KeyEventArgs e)
    {
        if (IsValidKey((int)e.Key))
            return;
        e.Handled = true;
        this.CaretIndex = this.Text.Length;
    }
    private void PastingEventHandler(object sender, DataObjectEventArgs e)
    {
        // Prevent/disable paste
        e.CancelCommand();
    }
    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();
        DataObject.AddCopyingHandler(this, PastingEventHandler);
        DataObject.AddPastingHandler(this, PastingEventHandler);
        this.CaretIndex = this.Text.Length;
        this.KeyDown += KeyPressed;
        this.KeyUp += KeyReleased;
        this.PreviewMouseDown += MouseClicked;
        this.PreviewMouseUp += MouseReleased;
        this.TextChanged += ValueChanged;
        this.Text = Format(string.Empty);
    }
    public decimal? Value
    {
        get { return (decimal?)this.GetValue(ValueProperty); }
        set { this.SetValue(ValueProperty, value); }
    }
    public static readonly DependencyProperty ValueProperty = DependencyProperty.Register(
        "Value",
        typeof(decimal?),
        typeof(CurrencyTextBox),
        new FrameworkPropertyMetadata(new decimal?(), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, new PropertyChangedCallback(ValuePropertyChanged)));
    private static void ValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        ((CurrencyTextBox)d).Value = ((CurrencyTextBox)d).FormatBack(e.NewValue.ToString());
    }
}

和 xaml：

<myNamespace:CurrencyTextBox
    Value="{Binding Path=DataContext.MyDecimalProperty, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}"
    CurrencySymbol="R$ "
    Culture="pt-BR"
    CurrencyDecimalPlaces="2"
    DecimalSeparator=","
    ThousandSeparator="." />