摘自:http://www.cnblogs.com/risen/archive/2008/01/15/1039751.html

public partial class AlertForm : Form
    {
        /*
         * 在类AlertForm定义的下方，
         * 我们创建用于显示的字符串和其颜色的变量，
         * 再定义几个Rectangle对象的变量用于放置标题、
         * 提示内容以及可以拖动窗体的区域和关闭按钮的区域。
         * 然后，我们需要保存窗体在浮动时的高度以便计算移动后的新高度，
         * intervalValue变量用来确定窗体显示和隐藏的速度。
         * 进行平台调用时我们需要提前定义好常量的值用来传递给函数，
         * WM_NCLBUTTONDOWN和HT_CAPTION常量用于拖动窗体，
         * 他们的值都保存在WinUser.h头文件中，
         * 所对应的动态链接库名为：user32.dll。
         * 我们用到的Win32API为：SendMessage、ReleaseCapture和ShowWindow，
         * 通过使用DllImportAttribute可以导入相应的函数并在程序中重新进行定义，如下：
         */
        public Bitmap BackgroundBitmap = null;

        private string titleText;
        private string contentText;
        private Color normalTitleColor = Color.FromArgb(0, 0, 0);
        private Font normalTitleFont = new Font("宋体", 12, FontStyle.Regular, GraphicsUnit.Pixel);
        private Color normalContentColor = Color.FromArgb(0, 0, 0);
        private Font normalContentFont = new Font("宋体", 12, FontStyle.Regular, GraphicsUnit.Pixel);

        public Rectangle TitleRectangle;
        public Rectangle TitlebarRectangle;
        public Rectangle ContentRectangle;
        public Rectangle CloseBtnRectangle;

        private Rectangle WorkAreaRectangle;

        private int SavedTop;
        private int currentTop = 1;
        private int intervalValue = http://www.mamicode.com/2;

        public const int WM_NCLBUTTONDOWN = 0x00A1; //消息:左键点击 winuser.h
        public const int HT_CAPTION = 0x0002; //标题栏

        [DllImportAttribute("user32.dll")]
        public static extern int SendMessage(IntPtr hWnd, int Msg, int wParam, int lParam); //发送消息 //winuser.h 中有函数原型定义
        [DllImportAttribute("user32.dll")]
        public static extern bool ReleaseCapture(); //释放鼠标捕捉 winuser.h
        /*
         * SendMessage向消息循环发送标题栏被按下的消息来模拟窗体的拖动，
         * ShowWindow用来将特定句柄的窗体显示出来，
         * 注意第二个参数nCmdShow，它表示窗体应该怎样显示出来，
         * 而我们需要窗体不获得焦点显示出来，
         * SW_SHOWNOACTIVATE可以满足我们要求，
         * 继续在WinUser.h文件中搜索找到该常量对应的值为4，
         * 于是我们就可以这样调用来显示窗体了：
         */
        [DllImportAttribute("user32.dll")] //winuser.h
        private static extern Boolean ShowWindow(IntPtr hWnd, Int32 nCmdShow);

        public int CurrentState=0; //0=hide 1=uptoshow 2=showing 3=downtohide        

        private AlertForm()
        {
            InitializeComponent();
            SetBackgroundBitmap(snnu.ccs.Properties.Resources.popup2, Color.FromArgb(255, 0, 255));
        }
        public static void Show(string ftitletext, string fcontenttext)
        {
            AlertForm alert = new AlertForm();
            alert.ShowForm(ftitletext, fcontenttext);
        }
        /*
         * 当窗体需要升起时将窗体的Top属性值不断减少，
         * 而窗体回落时将Top属性值增加并超过屏幕的高度窗体就消失了，
         * 虽然原理很简单但仍需精确控制。
         * SetBackgroundBitmap函数首先将窗体背景图像保存到BackgroundBitmap变量中，
         * 然后根据该位图图像轮廓和透明色创建Region，BitmapToRegion就用于完成Bitmap到Region的转换，
         * 程序再将这个Region付值给窗体的Region属性以完成不规则窗体的创建。
         */
        protected void SetBackgroundBitmap(Image image, Color transparencyColor)
        {
            BackgroundBitmap = new Bitmap(image);
            Width = BackgroundBitmap.Width;
            Height = BackgroundBitmap.Height;
            TitleRectangle = new Rectangle(2, 1, 70, 25);
            TitlebarRectangle = new Rectangle(1, 1, Width, 25);
            ContentRectangle = new Rectangle(1, 25, Width, Height - 25);
            CloseBtnRectangle = new Rectangle(Width - 25, 1, 25, 25);
            Region = BitmapToRegion(BackgroundBitmap, transparencyColor);
        }

        protected Region BitmapToRegion(Bitmap bitmap, Color transparencyColor)
        {
            if (bitmap == null)
                throw new ArgumentNullException("Bitmap", "Bitmap cannot be null!");

            int height = bitmap.Height;
            int width = bitmap.Width;

            GraphicsPath path = new GraphicsPath();

            for (int j = 0; j < height; j++)
                for (int i = 0; i < width; i++)
                {
                    if (bitmap.GetPixel(i, j) == transparencyColor)
                        continue;

                    int x0 = i;

                    while ((i < width) && (bitmap.GetPixel(i, j) != transparencyColor))
                        i++;

                    path.AddRectangle(new Rectangle(x0, j, i - x0, 1));
                }

            Region region = new Region(path);
            path.Dispose();
            return region;
        }

        protected void DrawText(Graphics grfx)
        {
            if (titleText != null && titleText.Length != 0)
            {
                StringFormat sf = new StringFormat();
                sf.Alignment = StringAlignment.Near;
                sf.LineAlignment = StringAlignment.Center;
                sf.FormatFlags = StringFormatFlags.NoWrap;
                sf.Trimming = StringTrimming.EllipsisCharacter;
                grfx.DrawString(titleText, normalTitleFont, new SolidBrush(normalTitleColor), TitleRectangle, sf);
            }

            if (contentText != null && contentText.Length != 0)
            {
                StringFormat sf = new StringFormat();
                sf.Alignment = StringAlignment.Center;
                sf.LineAlignment = StringAlignment.Center;
                sf.FormatFlags = StringFormatFlags.MeasureTrailingSpaces;
                sf.Trimming = StringTrimming.Word;    
                grfx.DrawString(contentText, normalContentFont, new SolidBrush(normalContentColor), ContentRectangle, sf);
            }
        }
        /*
         * 通知窗体背景以及文字的绘制在重载的OnPaintBackground方法中完成，
         * 而且利用了双重缓冲区技术来进行绘制操作，代码如下：
         */
        protected override void OnPaintBackground(PaintEventArgs e)
        {
            Graphics grfx = e.Graphics;
            grfx.PageUnit = GraphicsUnit.Pixel;

            Graphics offScreenGraphics;
            Bitmap offscreenBitmap;

            offscreenBitmap = new Bitmap(BackgroundBitmap.Width, BackgroundBitmap.Height);
            offScreenGraphics = Graphics.FromImage(offscreenBitmap);

            if (BackgroundBitmap != null)
            {
                offScreenGraphics.DrawImage(BackgroundBitmap, 0, 0, BackgroundBitmap.Width, BackgroundBitmap.Height);
            }

            DrawText(offScreenGraphics);

            grfx.DrawImage(offscreenBitmap, 0, 0);
        }
        /*
         * CurrentState变量表示窗体的状态是显示中、停留中还是隐藏中，
         * 两个计时器根据窗体不同状态对窗体的位置进行更改，
         * 我们会使用SetBounds来执行该操作：
         * this.SetBounds(WorkAreaRectangle.Width - this.Width, WorkAreaRectangle.Height - currentTop, this.Width, this.Height);
         */
        protected void ShowForm(string ftitletext, string fcontenttext)
        {
            titleText = ftitletext;
            contentText = fcontenttext;
            WorkAreaRectangle = Screen.GetWorkingArea(WorkAreaRectangle);
            this.Top = WorkAreaRectangle.Height + this.Height;
            FormBorderStyle = FormBorderStyle.None;
            WindowState = FormWindowState.Normal;
            this.SetBounds(WorkAreaRectangle.Width - this.Width, WorkAreaRectangle.Height - currentTop, this.Width, this.Height);
            CurrentState = 1;
            timer1.Enabled = true;

            ShowWindow(this.Handle, 4); //#define SW_SHOWNOACTIVATE   4
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            if (CurrentState == 1)
            {
                this.SetBounds(WorkAreaRectangle.Width - this.Width, WorkAreaRectangle.Height - currentTop, this.Width, this.Height);
                currentTop = currentTop + intervalValue;
                if (this.Top <= WorkAreaRectangle.Height - this.Height)
                {
                    timer1.Enabled = false;
                    CurrentState = 2;
                    timer2.Enabled = true; //显示停留计时
                    currentTop = 1;
                }
            }
            else if (CurrentState==3)
            {
                this.SetBounds(WorkAreaRectangle.Width - this.Width, SavedTop + currentTop, this.Width, this.Height);
                currentTop = currentTop + intervalValue;
                if (this.Top >= WorkAreaRectangle.Height)
                {
                    timer1.Enabled = false;

                    this.Close();
                    CurrentState = 0;
                    currentTop = 1;
                }
            }
        }
        /*
         上述代码首先返回窗体绘制表面的Graphics并保存在变量grfx中，
         * 然后创建一个内存Graphics对象offScreenGraphics和内存位图对象offscreenBitmap，
         * 将内存位图对象的引用付值给offScreenGraphics，
         * 这样所有对offScreenGraphics的绘制操作也都同时作用于offscreenBitmap，
         * 这时就将需要绘制到通知窗体表面的背景图像BackgroundBitmap绘制到内存的Graphics对象上，
         * DrawText函数根据需要显示文字的大小和范围调用Graphics.DrawString将文字显示在窗体的特定区域。
         * 最后，调用Graphics.DrawImage将内存中已经绘制完成的图像显示到通知窗体表面。
         * 我们还需要捕获窗体的鼠标操作，有三个操作在这里进行，
         * 1、处理拖动窗体操作，
         * 2、处理通知窗体的关闭操作，
         * 3、内容区域的单击操作。
         * 三个操作都需要检测鼠标的当前位置与每个Rectangle区域的包含关系，
         * 只要单击落在特定区域我们就进行相应的处理，代码如下
         */
        private void TaskbarForm_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                if (TitlebarRectangle.Contains(e.Location)) //单击标题栏时拖动
                {
                    ReleaseCapture(); //释放鼠标捕捉
                    SendMessage(Handle, WM_NCLBUTTONDOWN, HT_CAPTION, 0); //发送左键点击的消息至该窗体(标题栏)
                }
                if (CloseBtnRectangle.Contains(e.Location)) //单击Close按钮关闭
                {
                    this.Close();
                    currentTop = 1;
                }
            }
        }

        private void timer2_Tick(object sender, EventArgs e)
        {
            timer2.Enabled = false;
            CurrentState = 1;
            currentTop = 1;
            SavedTop = this.Top;
            CurrentState = 3;
            timer1.Enabled = true;
        }

        private void TaskbarForm_MouseMove(object sender, MouseEventArgs e)
        {
            if (ContentRectangle.Contains(e.Location))
            {
                Cursor = Cursors.Hand;
            }
            else
                Cursor = Cursors.Default;
        }
    }