Dictionary error: Item with this key already has been added

Question

我在 foreach 循环中向 Dictionary 添加项目，我发现一旦抛出此错误 - 确实有代码尝试使用相同的键添加第二次项目，我不知道这在 foreach 中是如何发生的环形。这是代码：

private void ImportData()
{
    try
    {
        var a = (from b in _db.LinkData
                 join c in _db.Links on b.ParentLinkId equals c.Id
                 where c.IsParsed == null & c.LinkAddress.Contains("olx.ae")
                 select b).Take(500).Distinct().ToList();
        Dictionary<int?, long?> id = new Dictionary<int?, long?>();
        if (a.Any())
        {
            foreach (var x in a)
            {
                HHserviceClient hh = new HHserviceClient();
                var rs = new HHResponse();
                var rq = new HHPostPropertyRequest
                {
                    Amenities = x.Amenities,
                    Area = x.Area,
                    BathRooms = x.BathRooms,
                    Bedrooms = x.Bedrooms,
                    City = x.City,
                    Company = x.Company,
                    Contact = x.Contact,
                    Country = x.Country,
                    CustomerID = 1000,
                    Description = x.Description,
                    Email = x.Email,
                    LandLineNo = x.LandLineNo,
                    Lattitude = x.Lattitude,
                    Location = x.Location,
                    Longitude = x.Longitude,
                    MobileNo = x.MobileNo,
                    Prptype = x.Prptype,
                    PrpSource = x.PrpSource,
                    Price = x.Price,
                    Parkings = x.Parkings,
                    Title = x.Title
                };
                rs = hh.PostProperty(rq);
                if (rs.ID.HasValue)
                {
                    //Error thrown here 
                    id.Add(x.ParentLinkId, rs.ID);
                }
                else
                {
                    continue;
                }
            }
        }
        UpdateLink(id);
    }
    catch (Exception ex)
    {
        throw new Exception(ex.Message);
    }
}

Answer 1

如果键已经存在于字典中，您可以避免异常检查：

if (!id.ContainsKey(x.ParentLinkId)
    id.Add(x.ParentLinkId, rs.ID);

记住这个，来自 MSDN：

If you want to return distinct elements from sequences of objects of some custom data type, you have to implement the IEquatable generic interface in the class.

更多信息在这里：

Enumerable.Distinct Method (IEnumerable)

Answer 2

您不必使用 Add()

id[x.ParentLinkId] = rs.ID;

Dictionary error: Item with this key already has been added

Dictionary error: Item with this key already has been added

c#

foreach

dictionary