f#默认值中的依赖属性不匹配

我正在尝试转换c#依赖属性，限制输入到组合框中的文本的最大长度为f#。该程序是一个MVVM程序，使用f#创建模型和视图模型，使用c#创建视图。工作的c#代码是这样的:

public class myComboBoxProperties
    {
        public static int GetMaxLength(DependencyObject obj)
        {
            return (int)obj.GetValue(MaxLengthProperty);
        }
        public static void SetMaxLength(DependencyObject obj, int value)
        {
            obj.SetValue(MaxLengthProperty, value);
        }
        // Using a DependencyProperty as the backing store for MaxLength. This enables animation, styling, binding, etc...
        public static readonly DependencyProperty MaxLengthProperty =
            DependencyProperty.RegisterAttached("MaxLength",
            typeof(int),
            typeof(myComboBoxProperties),
            new UIPropertyMetadata(OnMaxLengthChanged));
        private static void OnMaxLengthChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
        {
            if (obj is ComboBox)
            {
                ComboBox comboBox = (ComboBox)obj;
                comboBox.Loaded += (sender, e) =>
                {
                    TextBox textBox = comboBox.Template.FindName("PART_EditableTextBox", comboBox) as TextBox;
                    if (textBox != null)
                    {
                        textBox.SetValue(TextBox.MaxLengthProperty, args.NewValue);
                    }
                };
            }
        }
    }

f#代码如下:

type myComboBoxProperties() =
    static let OnMaxLengthChanged  (myobj1 : DependencyObject, args : DependencyPropertyChangedEventArgs)  =
        let comboBox = myobj1 :?> ComboBox
        comboBox.Loaded.Subscribe (fun _ -> 
                                    let textBox : TextBox = comboBox.Template.FindName("PART_EditableTextBox", comboBox) :?> TextBox 
                                    match textBox with
                                    | null -> ()
                                    |_ -> textBox.SetValue(TextBox.MaxLengthProperty, args.NewValue))
    static let MaxLengthProperty = DependencyProperty.RegisterAttached("MaxLength", typeof<int>, typeof<myComboBoxProperties>, new UIPropertyMetadata(OnMaxLengthChanged))
    static member GetMaxLength (myobj : DependencyObject) = myobj.GetValue(MaxLengthProperty) :?> int
    static member SetMaxLength (myobj : DependencyObject, value : int) = myobj.SetValue(MaxLengthProperty, value)

问题是，我得到的XAML错误是:

默认值type与属性类型MaxLength不匹配

我做错了什么?

open System.Windows
open System.Windows.Controls
type MyComboBoxProperties() =
  static let OnMaxLengthChanged  (myobj1 : DependencyObject) (args : DependencyPropertyChangedEventArgs) =
    let comboBox = myobj1 :?> ComboBox
    comboBox.Loaded.Add (
      fun _ -> 
        let textBox : TextBox = comboBox.Template.FindName("PART_EditableTextBox", comboBox) :?> TextBox 
        match textBox with
        | null -> ()
        |_ -> textBox.SetValue(TextBox.MaxLengthProperty, args.NewValue)
      )
  static let MaxLengthProperty = 
    DependencyProperty.RegisterAttached(
      "MaxLength", 
      typeof<int>, 
      typeof<MyComboBoxProperties>, 
      UIPropertyMetadata(0, PropertyChangedCallback OnMaxLengthChanged)
      )
  static member GetMaxLength (myobj : DependencyObject) = myobj.GetValue(MaxLengthProperty) :?> int
  static member SetMaxLength (myobj : DependencyObject, value : int) = myobj.SetValue(MaxLengthProperty, value)