Question

我不擅长编程，我不知道我的代码中发生了什么，它之前运行良好，但现在我收到了这个错误：

NullReferenceException未被用户代码取消。

对象引用未设置为对象的实例。

这是我的代码：

 void GetProfileInfo()
    {
        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandText = "SELECT FirstName, LastName, Address, ContactNo, EmailAddress FROM Users " +
            "WHERE UserID=@UserID";
        cmd.Parameters.Add("@UserID", SqlDbType.Int).Value = Session["userid"].ToString();
        SqlDataReader data = cmd.ExecuteReader();
        while (data.Read())
        {
            txtFN.Text = data["FirstName"].ToString();
            txtLN.Text = data["LastName"].ToString();
            txtAddress.Text = data["Address"].ToString();
            txtContact.Text = data["ContactNo"].ToString();
            txtEmail.Text = data["EmailAddress"].ToString();
        }
        con.Close();
    }

Answer 1

首先，您必须检查初始化Session["userid"]的所有事件，那么为了避免异常错误你必须检查这个变量值是否为null或用try catch finally块包装代码

前：

try
{
        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandText = "SELECT FirstName, LastName, Address, ContactNo, EmailAddress FROM Users " +
            "WHERE UserID=@UserID";
        cmd.Parameters.Add("@UserID", SqlDbType.Int).Value = Session["userid"].ToString();
        SqlDataReader data = cmd.ExecuteReader();
        while (data.Read())
        {
            txtFN.Text = data["FirstName"].ToString();
            txtLN.Text = data["LastName"].ToString();
            txtAddress.Text = data["Address"].ToString();
            txtContact.Text = data["ContactNo"].ToString();
            txtEmail.Text = data["EmailAddress"].ToString();
        }
}
catch(Exception e)
{
    string message = e.Message;
    MessageBox.Show(message);
}
finally
{
        con.Close();
}

错误：对象引用未设置为对象的实例

1 个答案: