/// <summary>
/// 打开MDI窗体,同一个窗体只能运行一个实例
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="parent"></param>

protected override void WndProc(ref Message msg)
{
        const int WM_SYSCOMMAND = 0x0112;

using (OleDbConnection conn = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=|DataDirectory|\\DB\\db1.mdb;Persist Security Info=True"))
{
    conn.Open();