c# - 错误 : The Out Parameter must be assigned before control leaves the current method

Question

发送回参数时出现此错误

Error : The Out Parameter must be assigned before control leaves the current method

代码是

 public void GetPapers(string web, out int Id1, out int Id2)
    {
        SqlConnection conn = new SqlConnection(ConnectionString());
        conn.Open();
        SqlCommand cmd = new SqlCommand("GetPapers", conn);
        cmd.CommandType = CommandType.StoredProcedure;

        cmd.Parameters.Add(new SqlParameter("@URL", String(web)));

        SqlDataReader rdr = cmd.ExecuteReader();

        if (rdr.Read())
        {
            Id1 = (int)rdr["ID1"];
            Id2 = (int)rdr["ID2"];
        }

        rdr.Close();
    }

称其为

GetPapers(web, out Id1, out Id2);

与此问题相关

Related question

Answer 1

您在 if 语句中分配 Id1 和 Id2，编译器无法确定它是否会在运行时分配一个值，因此会出现错误。

您可以在 if 语句之前为它们分配一些默认值。就像是。

Id1 = 0;
Id2 = 0;

if (rdr.Read())
{
    Id1 = (int)rdr["ID1"];
    Id2 = (int)rdr["ID2"];
}

或在条件的 else 部分指定一些默认值。

在控件离开函数之前，必须为 out 类型参数分配一些值。在您的情况下，编译器无法确定您的变量是否会被分配，因为它是在 if 语句中分配的。

参见:5.3 Definite assignment

At a given location in the executable code of a function member, a variable is said to be definitely assigned if the compiler can prove, by static flow analysis, that the variable has been automatically initialized or has been the target of at least one assignment.