WinForm全屏显示（不是最大化）

核心代码

 Boolean m_IsFullScreen = false;//标记是否全屏

//这是一个按键事件
 private void button5_Click(object sender, EventArgs e)
        {
            m_IsFullScreen = !m_IsFullScreen;//点一次全屏，再点还原。
            this.SuspendLayout();
            if (m_IsFullScreen)//全屏 ,按特定的顺序执行
            {
                SetFormFullScreen(m_IsFullScreen);

                this.FormBorderStyle = FormBorderStyle.None;
                this.WindowState = FormWindowState.Maximized;

                this.Activate();//激活窗体
            }
            else//还原，按特定的顺序执行——窗体状态，窗体边框，设置任务栏和工作区域
            {

                this.WindowState = FormWindowState.Normal;
                this.FormBorderStyle = FormBorderStyle.Sizable;

                SetFormFullScreen(m_IsFullScreen);
               this.Activate();
            this.ResumeLayout(false);
        }

调用的方法 

 public Boolean SetFormFullScreen(Boolean fullscreen)//, ref Rectangle rectOld
        {
            Rectangle rectOld = Rectangle.Empty;
            Int32 hwnd = 0;
            hwnd = FindWindow("Shell_TrayWnd", null);//获取任务栏的句柄

            if (hwnd == 0) return false;

            if (fullscreen)//全屏
            {
                ShowWindow(hwnd, SW_HIDE);//隐藏任务栏

                SystemParametersInfo(SPI_GETWORKAREA, 0, ref rectOld, SPIF_UPDATEINIFILE);//get屏幕范围
                Rectangle rectFull = Screen.PrimaryScreen.Bounds;//全屏范围
                SystemParametersInfo(SPI_SETWORKAREA, 0, ref rectFull, SPIF_UPDATEINIFILE);//窗体全屏幕显示
            }
            else//还原
            {
                ShowWindow(hwnd, SW_SHOW);//显示任务栏
                SystemParametersInfo(SPI_SETWORKAREA, 0, ref rectOld, SPIF_UPDATEINIFILE);//窗体还原
            }
            return true;
        }

系统的Dll 

        #region user32.dll

        public const Int32 SPIF_UPDATEINIFILE = 0x1;
        public const Int32 SPI_SETWORKAREA = 47;
        public const Int32 SPI_GETWORKAREA = 48;
        public const Int32 SW_SHOW = 5;
        public const Int32 SW_HIDE = 0;

        [DllImport("user32.dll", EntryPoint = "ShowWindow")]
        public static extern Int32 ShowWindow(Int32 hwnd, Int32 nCmdShow);

        [DllImport("user32.dll", EntryPoint = "FindWindow")]
        private static extern Int32 FindWindow(string lpClassName, string lpWindowName);

        [DllImport("user32.dll", EntryPoint = "SystemParametersInfo")]
        private static extern Int32 SystemParametersInfo(Int32 uAction, Int32 uParam, ref Rectangle lpvParam, Int32 fuWinIni);