C# Development Example-Customized Screenshot Tool (2) Create Project, Register Hotkeys, and Display the Screenshot Main Window

        private void Form1_Load(object sender, EventArgs e)
        {
            //隐藏窗口
            this.Hide();

            //注册快捷键
            //注：HotKeyId的合法取之范围是0x0000到0xBFFF之间，GlobalAddAtom函数得到的值在0xC000到0xFFFF之间，所以减掉0xC000来满足调用要求。
            this.hotKeyId = GlobalAddAtom("Screenshot") - 0xC000;
            if (this.hotKeyId == 0)
            {
                //如果获取失败，设定一个默认值；
                this.hotKeyId = 0xBFFE; 
            }

            if (this.HotKeyMode == 0)
            {
                RegisterHotKey(Handle, hotKeyId, (uint)KeyModifiers.Control | (uint)KeyModifiers.Alt, Keys.A);
            }
            else
            {
                RegisterHotKey(Handle, hotKeyId, (uint)KeyModifiers.Control | (uint)KeyModifiers.Shift, Keys.A);
            }
        }

        /// <summary>
        /// 处理快捷键事件
        /// </summary>
        /// <param name="m"></param>
        protected override void WndProc(ref Message m)
        {
            //if (m.Msg == 0x0014)
            //{
            //    return; // 禁掉清除背景消息
            //}
            const int WM_HOTKEY = 0x0312;
            switch (m.Msg)
            {
                case WM_HOTKEY:
                    ShowForm();
                    break;
                default:
                    break;
            }
            base.WndProc(ref m);
        }

        /// <summary>
        /// 如果窗口为可见状态，则隐藏窗口；
        /// 否则则显示窗口
        /// </summary>
        protected void ShowForm()
        {
            if (this.Visible)
            {
                this.Hide();
            }
            else
            {
                Bitmap bkImage = new Bitmap(Screen.AllScreens[0].Bounds.Width, Screen.AllScreens[0].Bounds.Height);
                Graphics g = Graphics.FromImage(bkImage);
                g.CopyFromScreen(new Point(0, 0), new Point(0, 0), Screen.AllScreens[0].Bounds.Size, CopyPixelOperation.SourceCopy);
                screenImage = (Bitmap)bkImage.Clone();
                g.FillRectangle(new SolidBrush(Color.FromArgb(64, Color.Gray)), Screen.PrimaryScreen.Bounds);
                this.BackgroundImage = bkImage;

                this.ShowInTaskbar = false;
                this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
                this.Width = Screen.PrimaryScreen.Bounds.Width;
                this.Height = Screen.PrimaryScreen.Bounds.Height;
                this.Location = Screen.PrimaryScreen.Bounds.Location;

                this.WindowState = FormWindowState.Maximized;
                this.Show();
            }
        }

        /// <summary>
        /// 当窗口正在关闭时进行验证
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (e.CloseReason == CloseReason.ApplicationExitCall)
            {
                e.Cancel = false;
                UnregisterHotKey(this.Handle, hotKeyId);
            }
            else
            {
                this.Hide();
                e.Cancel = true;
            }
        }