泛型List<T>排序（利用反射）

　　在最近一个项目中，有需求要对页面中所有的gridview添加排序功能。由于gridview的数据源绑定的是一个集合类List，而不是DataTable，所以无法使用DataView排序功能。另外，不同的gridview显示的是不同的业务数据，为了重用代码只能添加一个泛型方法，使用该方法对数据类型T，按照任意给定的属性进行排序。由于是要按照某个不固定的属性对List内的对象进行排序，所以修改类型T，使之实现IComparable接口，并利用List类的Sort () 方法进行排序是无法满足需求的。但是List类还提供了另一个Sort方法，它接受一个IComparer对象作为参数，在IComparer内可以实现排序的业务逻辑。唯一需要的就是进行排序的属性了，而这个在程序的上下文是已知的。

　　思路已经有了，但动手写代码前，google了一下相关文章，竟然发现有一段功能类似的代码，唯一不同是该该代码的实现中方法并不是泛型的。但是强大的地方是，代码中对实现的排序支持按照多个属性排序。于是稍加修改，一段强大的支持按照多属性对List进行排序的泛型方法就出炉了。

　　首先是表示排序属性和排序方向的类SortClass，其中保存了排序的属性和排序的方向。

    /// <summary>
    /// Class used to hold sort information
    /// </summary>
    public class SortClass
    {
        private string _sortProperty;
 
        public string SortProperty
        {
            get { return _sortProperty; }
            set { _sortProperty = value; }
        }
        private SortDirection _sortDirection;
 
        public SortDirection SortDirection
        {
            get { return _sortDirection; }
            set { _sortDirection = value; }
        }
 
        public SortClass(string sortProperty, SortDirection sortDirection)
        {
            _sortProperty = sortProperty;
            _sortDirection = sortDirection;
        }

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　　有了SortClass后就可以开始实现IComparar接口了。下面是Comparer的代码，它实现了IComparar接口，包含实际的排序功能。从代码中可以看出，Comparer通过递归调用CheckSort方法来首先按照多个属性排序的。

    /// <summary>
    /// Implementation of IComparer
    /// </summary>
    public class Comparer<T> : IComparer<T>
    {
        private List<SortClass> _sortClasses;
 
        /// <summary>
        /// Collection of sorting criteria
        /// </summary>
        public List<SortClass> SortClasses
        {
            get { return _sortClasses; }
        }
 
        /// <summary>
        /// Default Constructor
        /// </summary>
        public Comparer()
        {
            _sortClasses = new List<SortClass>();
        }
 
        /// <summary>
        /// Constructor that takes a sorting class collection as param
        /// </summary>
        /// <param name="sortClass">
        /// Collection of sorting criteria
        ///</param>
        public Comparer(List<SortClass> sortClass)
        {
            _sortClasses = sortClass;
        }
 
        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="sortProperty">Property to sort on</param>
        /// <param name="sortDirection">Direction to sort</param>
        public Comparer(string sortProperty, SortDirection sortDirection)
        {
            _sortClasses = new List<SortClass>();
            _sortClasses.Add(new SortClass(sortProperty, sortDirection));
        }
 
        /// <summary>
        /// Implementation of IComparer interface to compare to object
        /// </summary>
        /// <param name="x"></param>
        /// <param name="y"></param>
        /// <returns></returns>
        public int Compare(T x, T y)
        {
            if (SortClasses.Count == )
            {
                return ;
            }
            return CheckSort(, x, y);
        }
 
        /// <summary>
        /// Recursive function to do sorting
        /// </summary>
        /// <param name="sortLevel">Current level sorting at</param>
        /// <param name="myObject1"></param>
        /// <param name="myObject2"></param>
        /// <returns></returns>
        private int CheckSort(int sortLevel, T myObject1, T myObject2)
        {
            int returnVal = ;
            if (SortClasses.Count -  >= sortLevel)
            {
                object valueOf1 = myObject1.GetType().GetProperty(SortClasses[sortLevel].SortProperty).GetValue(myObject1, null);
                object valueOf2 = myObject2.GetType().GetProperty(SortClasses[sortLevel].SortProperty).GetValue(myObject2, null);
                if (SortClasses[sortLevel].SortDirection == SortDirection.Ascending)
                {
                    returnVal = ((IComparable)valueOf1).CompareTo((IComparable)valueOf2);
                }
                else
                {
                    returnVal = ((IComparable)valueOf2).CompareTo((IComparable)valueOf1);
                }
 
                if (returnVal == )
                {
                    returnVal = CheckSort(sortLevel + , myObject1, myObject2);
                }
            }
 
            return returnVal;
        }
    }

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　　准备工作完成后，就可以开始实现真正强大的泛型排序方法了。ListSorter提供了2个静态方法，一个用来对多个属性排序，另一个为了方便只针对一个属性进行排序的情况。

    public class ListSorter
    {
        public static List<T> SortList<T>(List<T> listToSort, List<string> sortExpression, List<SortDirection> sortDirection)
        {
            //check parameters
            if (sortExpression.Count != sortDirection.Count||sortExpression.Count==||sortDirection.Count==)
            {
                throw new Exception("Invalid sort arguments!");
            }
 
            //get myComparer
            Comparer<T> myComparer = new Comparer<T>();
            for (int i = ; i < sortExpression.Count; i++)
            {
                SortClass sortClass = new SortClass(sortExpression[i], sortDirection[i]);
                myComparer.SortClasses.Add(sortClass);
            }
             listToSort.Sort(myComparer);
             return listToSort;
        }
 
        public static List<T> SortList<T>(List<T> listToSort, string sortExpression, SortDirection sortDirection)
        {
            //check parameters
            if (sortExpression == null || sortExpression == string.Empty || sortDirection == null)
            {
                return listToSort;
            }
 
            Comparer<T> myComparer = new Comparer<T>();
            myComparer.SortClasses.Add(new SortClass(sortExpression, sortDirection));
            listToSort.Sort(myComparer);
            return listToSort;
        }
    }

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有了上面的代码，只需简单几行就可以轻松实现对泛型List的排序功能了：

    List<Project> projectList=...;
    List<Project> sortedProject = ListSorter.SortList(projectList, "Name", SortDirection.Ascending);

出处：http://www.cnblogs.com/dytes/archive/2009/01/06/1370623.html