c# - InvalidOperationException 当我尝试从数据库中检索密码时， "Invalid attempt to read when no data is present."

Question

这是我的代码，我需要从数据库中检索LoginPassword

public partial class frmPassword : Form
{
    SqlConnection connection = new SqlConnection(@"Data Source=WORKSTATION\SQLEXPRESS;Initial Catalog=TPSystem;Integrated Security=True");

    public frmPassword()
    {
        InitializeComponent();
    }

    private void btnUpdatePassword_Click(object sender, EventArgs e)
    {
        frmLogin login = new frmLogin();
        string UserN = login.UName;
        string Pass;
        SqlCommand cmd = new SqlCommand("SELECT Login_Password FROM AdminLogin WHERE Login_Username = '"+UserN+"'", connection);

        try
        {
            connection.Open();
            SqlDataReader reader = cmd.ExecuteReader();
            reader.Read();

            Pass = reader["Login_Password"].ToString();

            if (tbOldPassword.Text == Pass)
                MessageBox.Show("Password matches");
            else
                MessageBox.Show("Password wrong");
            reader.Close();
        }
        catch (SqlException ex)
        {
            MessageBox.Show(ex.Message, "Report", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Error);
        }
        finally
        {
            connection.Close();
        }
    }
}

我在执行时遇到了这个错误:

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll

Additional information: Invalid attempt to read when no data is present.

Answer 1

reader.Read() 方法返回一个 bool 值以指示是否确实读取了任何内容——您根本没有检查它....

将您的代码更改为:

if(reader.Read())
{
    Pass = reader["Login_Password"].ToString();

    if (tbOldPassword.Text == Pass)
            MessageBox.Show("Password matches");
    else
            MessageBox.Show("Password wrong");
}

如果没有任何内容被读取，我猜你的用户不存在 - 我不确定你想在那种情况下做什么......由你决定

但是请告诉我您不是以明文存储密码> 在你的数据库中!!!!