针对 ObjectDataSource 的客户对象通用排序 (ASP.NET)

引言

PropertyComparer 类为数据访问组件提供了在利用 ObjectDataSource 时启用客户对象排序的可能性。

背景

ASP.NET 2.0 包含 GridView 和 ObjectDataSource 控制。您可以定义 ObjectDataSource 使用数据访问组件的哪些方法。如果 Select 方法返回 DataSet 或 DataTable，则可以开箱即用地为 GridView 使用分页和排序。

如果您想使用业务对象集合而不是 DataSet/DataTable，则必须自己实现排序。我编写了一个通用比较器，用于所有我的业务对象。

使用代码

使用一个 GridView，其中定义了 DataSourceId，并启用排序

<asp:GridView     ID="exampleGridView" runat="server" 
        DataSourceID="exampleDataSource" 
        AllowSorting="True" ... >

定义 ObjectDataSource

<asp:ObjectDataSource     ID="exampleDataSource" runat="server" 
            TypeName="ExampleDataAccessComponent" 
            SelectMethod="Select" 
            SortParameterName="orderBy" ... >

编写实现 Select 方法的数据访问组件

[DataObject()]
public sealed class ActivityDac
{
    private string myConnectionString;
    private DbProviderFactory myFactory;


    public ActivityDac()
    {
        ConnectionStringSettings cs = 
           ConfigurationManager.ConnectionStrings[" ... "];
        myFactory = DbProviderFactories.GetFactory(cs.ProviderName);
        myConnectionString = cs.ConnectionString;
    }


    [DataObjectMethod(DataObjectMethodType.Select, true)]
    public Activity[] Select(string orderBy)
    {
        List<BusinessClass> list = new List<BusinessClass>();
        using (DbConnection con = myFactory.CreateConnection())
        {
            con.ConnectionString = myConnectionString;
            using (DbCommand cmd = myFactory.CreateCommand())
            {
                cmd.Connection = con;
                cmd.CommandText = " ... ";

                DbParameter p = myFactory.CreateParameter();
                ...
                cmd.Parameters.Add(p);

                con.Open();
                DbDataReader reader = cmd.ExecuteReader(CommandBehavior.SingleResult);

                while (reader.Read())
                {
                    BusinessClass o = new BusinessClass(reader.GetInt32(0));
                    ..
                    list.Add(o);
                }
            }
        }

        if (!String.IsNullOrEmpty(orderBy))
        {
            PropertyComparer<BusinessClass> comparer = 
              new PropertyComparer<BusinessClass>(orderBy);
            list.Sort(comparer);
        }

        return list.ToArray();
    }
}

以下是 PropertyComparer 的代码

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Collections;

namespace Example
{
    public class PropertyComparer<T> : IComparer<T>
    {
        private enum SortType
        {
            Descending = -1,
            Ascending = 1
        }


        private SortType mySortDirecton;
        private string mySortPropertyName;


        public PropertyComparer(string sortString)
        {
            if (sortString == null)
                throw new ArgumentNullException("sortString");
            if (sortString.Length == 0)
                throw new ArgumentOutOfRangeException("sortString");

            if (sortString.ToLower().EndsWith(" desc"))
            {
                mySortPropertyName = sortString.Substring(0, sortString.Length - 5);
                mySortDirecton = SortType.Descending;
            }
            else
            {
                if (sortString.ToLower().EndsWith(" asc"))
                    mySortPropertyName = sortString.Substring(0, sortString.Length - 4);
                else
                    this.mySortPropertyName = sortString;

                this.mySortDirecton = SortType.Ascending;
            }
        }


        #region IComparer<T> Members

        public int Compare(T x, T y)
        {
            if ((x == null) && (y == null))
                return 0;
            if (x == null)
                return -(int)mySortDirecton;
            if (y == null)
                return (int)mySortDirecton;

            PropertyInfo p = x.GetType().GetProperty(mySortPropertyName);
            if (p == null)
                throw new ApplicationException();

            object vX = p.GetValue(x, null);
            object vY = p.GetValue(y, null);

            if ((vX == null) && (vY == null))
                return 0;
            if (vX == null)
                return -(int)mySortDirecton;
            if (vY == null)
                return (int)mySortDirecton;

            return (int)mySortDirecton * Comparer.DefaultInvariant.Compare(vX, vY);
        }

        #endregion
    }
}

历史

• 2008 年 10 月 24 日：9:23 - 更正了拼写错误。