登录事件

   private void btnlogin_Click(object sender, EventArgs e)
        {
            //登录按钮事件         
            try
            {
                //判断最后登录时间 是不是今天
                string s5 = "select * from Users where UserName=@u";
                SQLiteParameter p4 = new SQLiteParameter("@u",txtUserName.Text);
                DataTable d= SqliteHelper.ExecuteDatatable(s5, p4);
                if (Convert.ToDateTime(d.Rows[0]["LastLoginTime"]).ToString("yyyy-MM-dd")!=DateTime.Now.ToString("yyyy-MM-dd"))
                {
                    string s4 = "update Users set LastLoginTime=datetime('now','localtime'), LoginCount=0,ErrorCount=0 where UserName=@u";
                    SqliteHelper.ExecuteNonQuery(s4, p4);
                }

                if (txtPwd.Text.Trim() != "" && txtUserName.Text.Trim() != "")
                {
                    string s = "select count(*) from Users where UserName=@u and PassWord=@p";
                    SQLiteParameter[] p = { new SQLiteParameter("@u", txtUserName.Text), new SQLiteParameter("@p", txtPwd.Text) };
                    int i = Convert.ToInt32(SqliteHelper.ExecuteScalar(s, p));

                    if (i > 0)
                    {
                        string s1 = "select * from Users where UserName=@u and PassWord=@p";
                        SQLiteParameter[] p1 = { new SQLiteParameter("@u", txtUserName.Text), new SQLiteParameter("@p", txtPwd.Text) };
                        DataTable dt = SqliteHelper.ExecuteDatatable(s1, p1);


                        if (Convert.ToInt32(dt.Rows[0]["LoginCount"]) > 2)
                        {
                            string s2 = "update Users set Status = '禁用', LastLoginTime=datetime('now','localtime')  where UserName=@u and PassWord=@p";
                            SqliteHelper.ExecuteNonQuery(s2, p1);
                            MessageBox.Show("登陆次数超过3次，用户名已禁用");                        
                            txtUserName.Enabled = false;
                            txtPwd.Enabled = false;
                            return;
                        }
                        else
                        {
                            string s3 = "update Users set LoginCount = LoginCount+1 ,LastLoginTime=datetime('now','localtime')  where UserName='" + txtUserName.Text + "' and PassWord='" + txtPwd.Text + "'";
                            int count = SqliteHelper.ExecuteNonQuery(s3, null);
                            this.DialogResult = DialogResult.OK;
                        }
                    }
                    else
                    {
                        string s2 = "update Users set ErrorCount = ErrorCount + 1,LastLoginTime=datetime('now','localtime') where UserName='" + txtUserName.Text + "'";
                        int count = SqliteHelper.ExecuteNonQuery(s2, null);

                        string s1 = "select * from Users where UserName=@u";
                        SQLiteParameter[] p1 = { new SQLiteParameter("@u", txtUserName.Text)};
                        DataTable dt = SqliteHelper.ExecuteDatatable(s1, p1);

                        if (Convert.ToInt32(dt.Rows[0]["ErrorCount"]) > 4)
                        {
                            MessageBox.Show("错误次数超过5次，不可登录");
                        }
                        else
                        {
                            MessageBox.Show(("错误次数"+dt.Rows[0]["ErrorCount"].ToString()+"次"));
                        }
                    }
                }
                else
                {
                    MessageBox.Show("用户名或密码不能为空");
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("程序出现异常，异常原因：" + ex.Message);
            }
        }