为什么我的代码没有读取if语句中的下一个条件

Question

为什么我的代码无法读取if语句中的下一个条件？

MySqlCommand cmd = new MySqlCommand("Select * from admin where Username='" + txtuser.Text + "'  and Password='" + txtpass.Text + "' ", con);

dr = cmd.ExecuteReader();
if (dr.Read())
{
    if (txtuser.Text == dr["Username"].ToString() && txtpass.Text == dr["Password"].ToString())
    {

        this.Hide();
        Form f1 = new Form1();
        f1.Show();
    }
    else if (txtuser.Text != dr["Username"].ToString() && txtpass.Text == dr["Password"].ToString())
    {
        MessageBox.Show("Incorrect Username!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
        clear();
    }
    else if (txtuser.Text == dr["Username"].ToString() && txtpass.Text != dr["Password"].ToString())
    {
        MessageBox.Show("Incorrect Password!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
        clear();
    }
    else if (txtuser.Text == "" & txtpass.Text == "")
    {
        MessageBox.Show("Please Enter Username and Password!", "Message", MessageBoxButtons.OK,
            MessageBoxIcon.Error);

    }
    else if (txtuser.Text == "" && txtpass.Text != "")
    {
        MessageBox.Show("Please Enter Username!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
        clear();
    }
    else if (txtuser.Text != "" && txtpass.Text == "")
    {
        MessageBox.Show("Please Enter Password!", "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
        clear();
    }
    else if (txtuser.Text != dr["Username"].ToString() && txtpass.Text != dr["Password"].ToString())
    {
        MessageBox.Show("Incorrect Username and Password!", "Message", MessageBoxButtons.OK,
            MessageBoxIcon.Error);
        clear();
    }
}

Answer 1

在C＃中&&条件的情况下，如果第一个条件为假，则下一个条件将不被验证