Mdi悬浮子窗体不超过主窗体边界

        //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;
            }
        }