Question

在linq中，我正在尝试使用动态排序列创建gridview 谁能帮我解决下面的代码以及为何不起作用

// i created this function to get column value which i need to sorty by 
private static string GetReflectedPropertyValue( object subject, string field)
        {
            object reflectedValue = subject.GetType().GetProperty(field).GetValue(subject, null);
            return reflectedValue != null ? reflectedValue.ToString() : "";
        }

// this is my grid query 
List<ticketSearchRes> tickets = new List<ticketSearchRes>();
// here i deteermined sort direction ascending or desc
            bool asc = (gridViewInputsVM.SortDirection == "asc") ? true : false;
            bool desc = (gridViewInputsVM.SortDirection != "asc") ? true : false;
            IQueryable<ticketSearchRes> source = (from ticket in _db.TblTicket
                                                  where (searchRes.assignTic == 1) ? ticket.AssignedTo == CurrentuserId : true
                                                  where (searchRes.myTicket == 1 && searchRes.forOthers != 1) ? ticket.CreatedFor == CurrentuserId : true
                                                       orderby
                                                  asc ? GetReflectedPropertyValue(ticket, "TicketTitle") : "",
// here i need to get dynamic column which i need to sort by 
                                                  desc ? GetReflectedPropertyValue(ticket, "TicketTitle") : ""  descending  // doesn't work
                                                  select new ticketSearchRes
                                                  {
                                                      title = (ticket.TicketTitle != null) ? ticket.TicketTitle.ToString() : "",
                                                      ticId = ticket.TicketId.ToString()     
 }).AsQueryable();

Answer 1

我该如何解决；

部分类TicketSearchResList是填充部分方法CustomSort的部分。 CustomSort接受属性名称和排序方向，并使用Reflection对命名的属性进行排序。到目前为止，应该很容易理解。

public partial class TicketSearchResList : List<TicketSearchRes>
{
    partial void CustomSort(string propertyName, string direction);

    public void Dump()
    {
        CustomSort("TicketTitle", "desc");

        foreach(var ticket in this)
            Console.WriteLine(ticket.ToString()); // For demo purposes
    }
}


public partial class TicketSearchResList {

    private string propertyName;
    private string direction;

    partial void CustomSort(string propertyName, string direction)
    {
        this.propertyName = propertyName;
        this.direction = direction;
        Sort(Comparer);
    }

    private int Comparer(TicketSearchRes x, TicketSearchRes y)
    {
        int directionChanger = direction == "asc" ? 1 : -1;

        try
        {
            PropertyInfo lhs = x.GetType().GetProperty(propertyName);
            PropertyInfo rhs = y.GetType().GetProperty(propertyName);     

            object o1 = lhs.GetValue(x, null);
            object o2 = rhs.GetValue(y, null);

            if(o1 is IComparable && o2 is IComparable)
            {
                return ((IComparable)o1).CompareTo(o2) * directionChanger;
            }

            // No sort
            return 0;
        }
        catch(Exception ex)
        {
            Debug.WriteLine(ex.Message); // Should log something
            return 0;
        }
    }

使用Comparer方法中的Reflection完成比较。方向是用于确定将结果乘以1还是-1。 CompareTo返回一个整数，其中-1表示小于，0表示等于，而1表示大于。因此，如果将结果乘以-1，就可以改变排序的方向。

最后，TicketSearchResList类继承自List<TicketResearchRes>。如您所见，Dump方法调用CustomSort，如果实现，它会产生有序的输出。

另外，请查看由Microsoft here记录的Sort方法

动态排序列在linq中不起作用

1 个答案: