private void btlogin_Click(object sender, EventArgs e){string username = null; string password = null ; if (tbusername、Text == ””) { MessageBox、Show("您没有输入用户名!","错误提示"); return; } if (tbmima、Text == "") { MessageBox、Show("您没有输入密码!","错误提示"); return; } DataSet dst = new DataSet();string connstr = ”Data Source=(local);Initial Catalog=Message;Integrated Security=True";SqlConnection con = new SqlConnection(connstr);con、Open();string str = "select * from 登录”;SqlDataAdapter sda = new SqlDataAdapter(str, con);SqlmandBuilder scd = new SqlmandBuilder(sda);sda、Fill(dst, "tong");dataGridView1、DataSource = dst、Tables[”tong”]、DefaultView;username = dataGridView1、Rows[0]、Cells[0]、Value、ToString()、Trim();password = dataGridView1、Rows[0]、Cells[1]、Value、ToString()、Trim();if (tbusername、Text、Equals(username) && tbmima、Text、Equals(password)){ Form2 f2 = new Form2(); f2、Visible = true; this、Visible = false;}else{ MessageBox、Show("您输入得用户名或密码错误","错误提示”); tbusername、Clear(); tbmima、Clear();} con、Close();}private void btcancel_Click(object sender, EventArgs e){ if (MessageBox、Show("您就是否真得想退出系统?”, "提示", MessageBoxButtons、YesNo) != DialogResult、No) { this、Close(); }}private void button1_Click(object sender, EventArgs e){ string username = null; string password = null; if (tbusername、Text == ”") { MessageBox、Show(”您没有输入用户名!”, "错误提示"); return;}if (tbmima、Text == "”){ MessageBox、Show("您没有输入密码!”, ”错误提示"); return;}DataSet dst...