wpf自定义控件报错：默认值类型与“IsChecked”属性的类型不匹配。

想写个WPF自定义控件，在里面加了一个checkbox，然后注册了一个依赖项用来暴露给外界以便于获取isChecked状态，现报错：
错误 XDG0062 默认值类型与“IsChecked”属性的类型不匹配。 FileOperator C:\Users\admin\source\repos\FileOperator\FileOperator\MainWindow.xaml 70

依赖项定义：

public Nullable<Boolean> CheckBoxIsChecked
        {
            get { return (Nullable<Boolean>)GetValue(CheckBoxIsCheckedProperty); }
            set { SetValue(CheckBoxIsCheckedProperty, value); }
        }

        // Using a DependencyProperty as the backing store for ChcckBoxIsChecked.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty CheckBoxIsCheckedProperty =
            DependencyProperty.Register("IsChecked", typeof(Nullable<Boolean>), typeof(FileControl), new PropertyMetadata("CheckBox",new PropertyChangedCallback(onCheckBoxChanged)));

        static void onCheckBoxChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
        {
            ((FileControl)sender).OnCheckBoxValueChanged(args);
        }

        private void OnCheckBoxValueChanged(DependencyPropertyChangedEventArgs e)
        {
            bool temp = bool.Parse(e.NewValue.ToString());
            this.checkBox.IsChecked = (Nullable < Boolean >) temp;
        }

使用控件代码：

<local:FileControl />

        public static readonly DependencyProperty CheckBoxIsCheckedProperty =
            DependencyProperty.Register("IsChecked", typeof(Nullable<Boolean>), typeof(FileControl), new PropertyMetadata("CheckBox", new PropertyChangedCallback(onCheckBoxChanged)));

属性是Nullable<Boolean>类型，PropertyMetadata默认值题主传递了字符串，改为布尔值===>


        public static readonly DependencyProperty CheckBoxIsCheckedProperty =
            DependencyProperty.Register("IsChecked", typeof(Nullable<Boolean>), typeof(FileControl), new PropertyMetadata(false, new PropertyChangedCallback(onCheckBoxChanged)));

有帮助麻烦点个采纳【本回答右上角】，谢谢~~