“输入字符串的格式不正确。”C＃

Question

groupID is a number of checkboxes. I am trying to create a comma separated list of UserIDs. GroupIDs identify a group with a number of users as a member. So I have:

      string groupIds = Request.Form["groupID"];
        if (groupIds!=null){
            string[] arrayOfGroupIds = groupIds.Split(','); //possible error here if only one checkbox is ticked?
            foreach (string id in arrayOfGroupIds){
                var users = db.Query("SELECT guestID FROM userGroups WHERE id = @0", id);
                foreach(var user in users){
                    userIds += user.guestID + ",";
                }
            }
        }   
        userIds += Request.Form["userId"] + "," + yourID;

On my next page I then call :

string userIDs = Request.Form["userIDs"];
string[] userIdsArray = userIDs.Split(',');
foreach(string userID in userIdsArray){
if(Convert.ToInt32(userID) == loggedID) { //ERROR HERE
        db.Execute("INSERT INTO Membership(GroupId,UserId) VALUES (@0, @1)", groupID, userID);
    }

Which results in the error in the title.

What could be causing this ?

Answer 1

Obviously the userID in the error line can't convert to an integer. You can add a break point, and see what value the variable actually is, and then modify your code.

BTW, you can convert in a more secure way. Like

int userIDInt;
if (int.TryParse(userID, out userIDInt))
{
    if (userIDInt == loggedID)
       // ...
}
else
    // handle the error