使用SQL的自定义控件 [英] Custom Control with SQL

问题描述

我想创建一个从SQL检索数据的控件.
我试过了

I want to create a control which retrieve data from SQL.
I tried

public partial class ComboSession : ComboBox
    {
        private ComboBox m_com = new ComboBox(); 
        public ComboBox Combo1
        {
            get { return m_com; }
            set { m_com = value; Invalidate(); }
        }
        public ComboSession()
        {
            
        }
        protected override void OnPaint(PaintEventArgs pe)
        {
            base.OnPaint(pe);
            try
            {
                string connectionString = "Data Source=";
                SqlConnection database = new SqlConnection(connectionString);
                database.Open();
                string queryString = "select pt_session from pt_session order by pt_session";
                SqlCommand cmd = new SqlCommand(queryString, database);
                SqlDataReader dr = cmd.ExecuteReader();
                m_com.Items.Clear();
                while (dr.Read())
                {
                   m_com.Items.Add(dr.GetValue(0).ToString());                    
                }
                database.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }

这没有用.问题是什么?

This didnt work. What is the Problem???

推荐答案

除了在Paint事件处理程序中执行与绘画无关的事情外，还有什么?

为什么干嘛要那样做?

这里有很多问题:
1)您不可以在绘画事件中读取数据库-它们需要快速而清晰，否则UI会受到严重影响.
2)您需要查看连接字符串，这是一堆垃圾.
3)您甚至都不显示组合框，这是一个主要优点，因为它可能会导致您的UI在永久的绘画事件中被锁定...

What, apart from you doing non-paint related things in the Paint event handler?

Why the heck would you do something like that?

There are a number of problems here:
1) You don''t do database reading in paint events - they need to be quick and sharp or the UI is affected badly.
2) You need to look at connections strings, your is a pile of rubbish.
3) You don''t even display your combo box, which is a major advantage as it would probably cause your UI to lock up in a permanent paint event...

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