Silverlight: 为ComboBox实现SelectedValue属性

silverlight中的comboBox并不像一般asp.net的dropdownlist或winform中的comboBox,有selectedValue属性。因为在silverlight中使用comboBox使用selectedItem就基本上满足了需求，如果还不够可以再为相应Tag赋值就OK了。

下面主要说一下为comboBox扩展一个selectedValue属性，其实也很简单，只要为ComboBox注册一个就OK。

1.　　一个简单的效果图：

2.　　调用方法:

ComboBoxItemValueExtend cbmValueExtend = new ComboBoxItemValueExtend();
            cbmValueExtend.SelectionChanged += (sender, arg) =>
            {
                UI.Alert(cbmValueExtend.SelectedValue);
            };
            cbmValueExtend.ItemsSource = DepartmentDataSource();
            cbmValueExtend.DisplayMemberPath = "Name";
            cbmValueExtend.SelectedValuePath = "ID";

            Dialog dlg = new Dialog()
            {
                Height = 300,
                Width = 400,
                Title = "ComboBox's SelectedValue Sample",
                Content = new AutoGrid(3, 60, 180)
                {
                    Children = 
                    {
                        new Label(){Content = "请选择："},
                        cbmValueExtend
                    }
                }
            };
            dlg.Show();

3.　　ComboBoxItemValueExtend的实现代码

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Linq;

namespace Top.Windows.Settings
{
    public class ComboBoxItemValueExtend : ComboBox
    {
        #region DependencyProperty: SelectedValuePathProperty-----------------------------------------
        public static readonly DependencyProperty SelectedValuePathProperty = DependencyProperty.Register("SelectedValuePath", typeof(string), typeof(ComboBoxItemValueExtend), null);

        /// <summary>
        /// Set the name or path of the property that is value for each date item.
        /// </summary>
        public string SelectedValuePath
        {
            get
            {
                return (string)GetValue(ComboBoxItemValueExtend.SelectedValuePathProperty);
            }
            set
            {
                SetValue(ComboBoxItemValueExtend.SelectedValuePathProperty, value);
            }
        }
        #endregion DependencyProperty: SelectedValuePathProperty-----------------------------------------


        #region DependencyProperty: SelectedValueProperty-------------------------------------
        public static DependencyProperty SelectedValueProperty = DependencyProperty.Register("SelectedValue", typeof(object), typeof(ComboBoxItemValueExtend), new PropertyMetadata(new PropertyChangedCallback(SelectedValuePropertyChanged)));

        /// <summary>
        /// Get Selected Value in the comboBox's SelectedItme
        /// </summary>
        public object SelectedValue
        {
            get
            {
                return GetValue(SelectedValueProperty);
            }
            set
            {
                try
                {
                    var q = (from item in Items
                             where item.GetType().GetProperty(SelectedValuePath).GetValue(item, null).Equals(value)
                             select item).Single();
                    SelectedItem = q;
                }
                catch
                {
                    throw new Exception();
                }
            }
        }

        private static void SelectedValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            (d as ComboBoxItemValueExtend).SelectedValue = e.NewValue;
        }
        #endregion DependencyProperty: SelectedValueProperty-------------------------------------


        public ComboBoxItemValueExtend()
            : base()
        {
            base.SelectionChanged += new SelectionChangedEventHandler(ComboBoxItemValueExtend_SelectionChanged);
        }

        void ComboBoxItemValueExtend_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (SelectedItem != null && !string.IsNullOrEmpty(SelectedValuePath))
            {
                try
                {
                    SetValue(ComboBoxItemValueExtend.SelectedValueProperty, SelectedItem.GetType().GetProperty(SelectedValuePath).GetValue(SelectedItem, null));
                    var value = SelectedValue;
                }
                catch
                {
                    throw new Exception();
                }
            }
        }
    }
}

4.　　DepartmentDataSource()方法是获取一些测试数据

        public struct Department
        {
            public int ID { set; get; }
            public int ParentId { set; get; }
            public string Name { set; get; }
            public string Description { set; get; }
        }

        public List<Department> DepartmentDataSource()
        {
            List<Department> list = new List<Department>() { 
                new Department(){ID = 1, ParentId = 0, Name = "Namespace"},
                new Department(){ID = 2, ParentId = 1, Name = "Class"},                
                new Department(){ID = 3, ParentId = 1, Name = "Enum"},
                new Department(){ID = 4, ParentId = 2, Name = "Method"},
                new Department(){ID = 5, ParentId = 4, Name = "Attribute"},
                new Department(){ID = 6, ParentId = 5, Name = "Private"},
                new Department(){ID = 7, ParentId = 5, Name = "Publict"},
                new Department(){ID = 8, ParentId = 7, Name = "DepartmentDataSource()"},
            };
            return list;
        }

谢谢指导！

备注：

关于DependencyProperty的相关知道可以翻阅MSDN学习一下，里面有详细的介绍，这里不再复述！

http://msdn.microsoft.com/zh-cn/library/cc221408.aspx