c# - 无法将类型 'int?' 隐式转换为 'int' 。

Question

我收到错误消息“无法隐式转换类型‘int？’到'int'。在返回行的我的 OrdersPerHour 上存在显式转换(你是否缺少强制转换？)”。我不确定为什么，因为我的 C# 技能不是那么先进。任何帮助将不胜感激。

static int OrdersPerHour(string User)
{
    int? OrdersPerHour;
    OleDbConnection conn = new OleDbConnection(strAccessConn);
    DateTime curTime = DateTime.Now;        

    try
    {
        string query = "SELECT COUNT(ControlNumber) FROM Log WHERE DateChanged > #" + curTime.AddHours(-1) + "# AND User = '" + User + "' AND Log.EndStatus in ('Needs Review', 'Check Search', 'Vision Delivery', 'CA Review', '1TSI To Be Delivered');";
        OleDbCommand dbcommand = new OleDbCommand(query, conn);
        dbcommand.Connection.Open();
        dbcommand.CommandType = CommandType.Text;
        OrdersPerHour = (int?)dbcommand.ExecuteScalar();

        Console.WriteLine("Orders per hour for " + User + " is " + OrdersPerHour);            
    }
    catch (OleDbException ex)
    {

    }
    finally
    {
        conn.Close();
    }
    return OrdersPerHour;
}

Answer 1

那么您要将 OrdersPerHour 转换为 int?

OrdersPerHour = (int?)dbcommand.ExecuteScalar();

然而你的方法签名是int:

static int OrdersPerHour(string User)

两者必须匹配。

---

还有一个快速建议 -> 在查询中使用参数，例如:

string query = "SELECT COUNT(ControlNumber) FROM Log WHERE DateChanged > ? AND User = ? AND Log.EndStatus in ('Needs Review', 'Check Search', 'Vision Delivery', 'CA Review', '1TSI To Be Delivered')";
OleDbCommand dbcommand = new OleDbCommand(query, conn);
dbcommand.Parameters.Add(curTime.AddHours(-1));
dbcommand.Parameters.Add(User);