//1.设置父窗体(主窗体)的AutoScrollMinSize大于父窗体的Size //例如主窗体(400,400), AutoScrollMinSize(500,500) //2.设置主窗体的IsMdiContainer为true         private void Form2_Load(object sender, EventArgs e)         {
   //悬浮窗体             Form3 f3 = new Form3(); //制定悬浮Mid子窗体的父窗体是该主窗体             f3.MdiParent = this; //事件委托             f3.LocationChanged += new EventHandler(frm_LocationChanged);             f3.Show();         } //窗体位置改变事件         private void frm_LocationChanged(object sender, EventArgs e)         {
               Form frm = (Form)sender; if (frm.Location.X + frm.Width > this.Width)             {
   //15:悬浮窗体左右边界的宽度,根据实际情况微调                 frm.Left = this.Width - frm.Width - 15;             } if (frm.Location.X < 0)             {
                   frm.Left = 0;             } if (frm.Location.Y < 0)             {
                   frm.Top = 0;             } if (frm.Location.Y + frm.Height > this.Height)             {
   //40:悬浮窗体上下边界的高度,根据实际情况微调                 frm.Top = this.Height - frm.Height - 40;             }         }