winfrom窗体跳转问题
我的意思是用窗体设计了一个登录界面，登陆的账号密码我想是通过数据库验证账号密码是否正确。点击登录就跳转到主窗体。这个怎么弄？ 界面
[解决办法]
在登陆窗口中添加一个按钮，在这个按钮中添加下面的代码

//登入
int count = 0;
string connStr = "连接字符串，在你的程序中连接数据库时直接复制过来";
//1、写连接字符串，打开数据库的链接
SqlConnection conn = new SqlConnection(connStr);
conn.Open();

//2、发送sql语句命令，并执行
SqlCommand com = new SqlCommand();
//com.CommandText = "select username,password from users where username='" + this.textBox1.Text + "'";
com.CommandText = "select * from student";
com.CommandType = CommandType.Text;
com.Connection = conn;

SqlDataReader dr = com.ExecuteReader();

//3、查询出来的数据进行遍历

while (dr.Read())
{

string username = dr.GetString(0).Replace(" ", "");
string password = dr.GetString(1).Replace(" ", "");
if (username.Equals(this.IDtextBox.Text) && password.Equals(this.PasswortextBox.Text))

{
Count = 1;
}

}

//4、关闭数据库
dr.Close();
conn.Close();

if (Count == 1)
{
MessageBox.Show("登陆成功");
MainForm main = new MainForm();
main.Show();
}
else
{
this.textBox1.Text = "";
this.textBox2.Text = "";
MessageBox.Show("用户不存在，或者密码错误。请重新输入！");
}
MainForm main = new MainForm();
main.Show();
this.Hide();
[解决办法]

namespace mySchool
{
    public partial class Login : Form
    {
        public Login()
        {
            InitializeComponent();
        }

        private void btnYes_Click(object sender, EventArgs e) 
 
        {
            string userName = txtName.Text;
            string passwd = txtPwd.Text;
            string connectionString = "Data Source=orcl;User Id=mySchool;Password=my;";

            OracleConnection conn = new OracleConnection(connectionString);
            try {
                //连接数据库
                conn.Open();
                string sql = String.Format("select count(*) from users where username=\'{0}\' and " +
                                            "password=\'{1}\'", userName, passwd);
                //创建OracleCommand对象
                OracleCommand cmd = new OracleCommand(sql, conn);
                //CommandType设置为执行SQL语句
                cmd.CommandType = CommandType.Text;
                //执行CommandType.Text指定的操作
                int count = Convert.ToInt32(cmd.ExecuteScalar());
                //获取执行结果
                if (count == 1) {
                    MessageBox.Show("欢迎进入成绩管理系统！", "登陆成功", MessageBoxButtons.OK,
                                        MessageBoxIcon.Information); 
 
                    this.Visible = false;//隐藏登陆窗口
                    MainForm mainForm = new MainForm(conn);//创建主窗体
                    mainForm.Visible = true;//设主窗口可见
                }
                else {
                    MessageBox.Show("用户名或密码错误！", "登陆失败", MessageBoxButtons.OK,
                                    MessageBoxIcon.Error);
                }
            }
            catch (Exception ex) {
                MessageBox.Show(ex.Message.ToString());
            }
        }

        private void btnCancel_Click(object sender, EventArgs e)
        {
            txtName.Text = "";
            txtPwd.Text = "";
            txtName.Focus();
        }
    }
}