“System.string到system.guid强制转换无效”错误处理

描述：

利用id查找username时查询命令cmd.ExecuteScalar()报错，

public stringGetUsernameFromID(object userId)

    {

        stringusername = "";

        if(userId == null) returnusername;

        System.Data.SqlClient.SqlConnection conn = newSystem.Data.SqlClient.SqlConnection(TSConnectionString);

        System.Data.SqlClient.SqlCommand cmd = newSystem.Data.SqlClient.SqlCommand(

            "SELECT [UserName] FROM [TravelService].[dbo].[aspnet_Users] " +

            "WHERE [UserId] = @userid ", conn);

        cmd.Parameters.Add("@userid",System.Data.SqlDbType.UniqueIdentifier).Value = userId;

        try

        {

            conn.Open();

            username = (string)cmd.ExecuteScalar();

        }

        catch(System.Data.SqlClient.SqlException e)

        {

            thrownew System.Configuration.Provider.ProviderException("无T法¤¡§根¨´据Yid找¨°到Ì?用®?户¡ì名?（ꡧcommonclass）ê?\n\n描¨¨述º?信?息¡é为a：êo" + e.Message);

        }

        finally

        {

            conn.Close();

        }

        if(username == null) username = "";

        returnusername;

    }

 

提示说userId参数赋值时强制转换成guid类型无效，userId参数为函数参数，调用时是用object类型变量传递的：

        objectuserid = (object)DetailsView1.Rows[33].Cells[1].Text;

        DetailsView1.Rows[34].Cells[1].Text =cc.GetUsernameFromID(userid);

处理方法：

将调用时变量修改一下，直接用字符串变量取值并用guid函数转类型传递：

string userid = DetailsView1.Rows[33].Cells[1].Text;

DetailsView1.Rows[34].Cells[1].Text =cc.GetUsernameFromID(new Guid(userid));