首先你需要OrderBy
@Slace 编写的扩展方法here https://stackoverflow.com/questions/307512/how-do-i-apply-orderby-on-an-iqueryable-using-a-string-column-name-within-a-gene。全部归功于Slace https://stackoverflow.com/users/11388/slace一段很棒的代码以及迄今为止解决方案中最困难的部分!我对其进行了轻微修改以适应您的具体情况:
public static class QueryableExtensions
{
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string sortProperty, ListSortDirection sortOrder)
{
var type = typeof(T);
var property = type.GetProperty(sortProperty);
var parameter = Expression.Parameter(type, "p");
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var orderByExp = Expression.Lambda(propertyAccess, parameter);
var typeArguments = new Type[] { type, property.PropertyType };
var methodName = sortOrder == ListSortDirection.Ascending ? "OrderBy" : "OrderByDescending";
var resultExp = Expression.Call(typeof(Queryable), methodName, typeArguments, source.Expression, Expression.Quote(orderByExp));
return source.Provider.CreateQuery<T>(resultExp);
}
}
创建一个方法来对列表进行排序。在下面的方法中需要注意以下几点:
- The
List<string>
被转换为IQueryable<string>
since Enumerable
运算符不采用表达式树。
- 该方法以相反的顺序迭代排序列的列表(假设您要为列表中的第一项提供最高排序优先级)。
private void PrintVideoList(IEnumerable<string> sortColumns, ListSortDirection sortOrder)
{
var videos = this.GetVideos();
var sortedVideos = videos.AsQueryable();
foreach (var sortColumn in sortColumns.Reverse())
{
sortedVideos = sortedVideos.OrderBy(sortColumn, sortOrder);
}
// Test the results
foreach (var video in sortedVideos)
{
Console.WriteLine(video.Title);
}
}
然后您应该能够使用如下方法:
// These values are entered by the user
var sortColumns = new List<string> { "Width", "Title", "Height" };
var sortOrder = ListSortDirection.Ascending;
// Print the video list base on the user selection
this.PrintVideoList(sortColumns, sortOrder);