输入的字符串格式不正确（C＃）

Question

After running the page on a browser, i get the: Input string was not in a correct format.

List<int> TheGroupIds = new List<int>();
if (Request.QueryString["MultiAssignInteractionGrouIds"] != null 
    && Request.QueryString["MultiAssignInteractionGrouIds"] != "" 
    && Request.QueryString["MultiAssignInteractionGrouIds"] != "-2")
{
    string GroupIds = Request.QueryString["MultiAssignInteractionGrouIds"];
    TheGroupIds = GroupIds.Split(',').Select(int.Parse).ToList(); <= 'The error is HERE' 
    TheGroupIds = TheGroupIds.Distinct().ToList();
}  

Answer 1

Only the debugger knows, but maybe you have values like "1,2,,3,4" , then use this Split :

string groupIds = Request.QueryString["MultiAssignInteractionGrouIds"];
if (!string.IsNullOrEmpty(groupIds) &&  groupIds != "-2")
{
    TheGroupIds = groupIds.Split(new[]{ ','}, StringSplitOptions.RemoveEmptyEntries)
     .Select(int.Parse)
     .Distinct()
     .ToList(); 
}

Answer 2

String contains not only intgeres. You can filter you text or use this converter:

public static int? ToNullableInt(this string s)
{
    int i;
    if (int.TryParse(s, out i)) return i;
    return null;
}

And the filter nullable values. Usages:

var result = text.Split(';').Select(x => x.ToNullableInt()).Where(y => y != null).ToList();