實現效果：

知識運用：

　　API函式AnimateWindows

　　[DllImportAttribute("user32.dll")]
　　private static extern bool AnimateWindow(IntPtr hwnd,int dwTime,int dwFlags);

1. hwnd: IntPtr,視窗控制代碼
2. dwTime：動畫的持續時間
3. dwFlags：動畫型別選項　常量值如下

實現程式碼：　

        private const int AW_SLIDE = 0x00040000;
        private const int AW_VER_NEGATIVE = 0x00000008;
        private const int AW_HIDE = 0x00010000;
        public Form1()
        {
            InitializeComponent();
            AnimateWindow(this.Handle, 3000, AW_SLIDE + AW_VER_NEGATIVE);   //開始窗體動畫
        }
        [DllImportAttribute("user32.dll")]
        private static extern bool AnimateWindow(IntPtr hwnd,int dwTime,int dwFlags);   //重寫API函式用來執行窗體動畫顯示操作
        
        //繪製漸變背景  
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            Color sColor = Color.Green; //顏色1，2
            Color eColor = Color.Black;
            //例項化刷子  (上色域 開始色 結束色 顏色方向)
            Brush b = new LinearGradientBrush(this.ClientRectangle,sColor,eColor,LinearGradientMode.Vertical);
            g.FillRectangle(b,this.ClientRectangle);    //進行上色
        }

        private void Form1_FormClosed(object sender, FormClosedEventArgs e)
        {
            AnimateWindow(this.Handle, 3000, AW_SLIDE + AW_VER_NEGATIVE+AW_HIDE);   //結束窗體動畫
        }