/// <summary>
    /// wpf标题栏 右键菜单 中添加新项
    /// </summary>
    public partial class MainWindow : Window
    {
        private const int WM_SYSCOMMAND = 0x112;
        private const int MF_STRING = 0x0;
        private const int MF_SEPARATOR = 0x800;

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool AppendMenu(IntPtr hMenu, int uFlags, int uIDNewItem, string lpNewItem);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool InsertMenuItem(IntPtr hMenu, int uPosition, int uFlags, int uIDNewItem, String ipNewItem);

        private int SYSMENU_ABOUT_ID = 0x1;
        public MainWindow()
        {
            InitializeComponent();
            SourceInitialized += MainWindow_SourceInitialized;
        }

        #region 给wpf标题栏的右键菜单栏 添加 “关于”菜单项
        private void MainWindow_SourceInitialized(object sender, EventArgs e)
        {
            var handle = (new WindowInteropHelper(this)).Handle;
            IntPtr hSysMenu = GetSystemMenu(handle, false);
            AppendMenu(hSysMenu, MF_SEPARATOR, 0, String.Empty);
            AppendMenu(hSysMenu, MF_STRING, SYSMENU_ABOUT_ID, "关于");
        } 
        #endregion

        #region 模拟实现 winform程序中的WndProc方法
        protected override void OnSourceInitialized(EventArgs e)
        {
            base.OnSourceInitialized(e);
            HwndSource source = PresentationSource.FromVisual(this) as HwndSource;
            source.AddHook(WndProc);
        }
        private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            // Handle messages...  
            if ((msg == WM_SYSCOMMAND) && ((int)wParam == SYSMENU_ABOUT_ID))
            {
                //表示监听到 关于菜单 按钮的 点击事件，并执行以下操作
                System.Windows.MessageBox.Show("good");
            }
            return IntPtr.Zero;
        } 
        #endregion
    }

private const int WM_SYSCOMMAND = 0x112;
        private const int MF_STRING = 0x0;
        private const int MF_SEPARATOR = 0x800;

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool AppendMenu(IntPtr hMenu, int uFlags, int uIDNewItem, string lpNewItem);

        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern bool InsertMenuItem(IntPtr hMenu, int uPosition, int uFlags, int uIDNewItem, String ipNewItem);

        private int SYSMENU_ABOUT_ID = 0x1;

        protected override void OnHandleCreated(EventArgs e)
        {
            base.OnHandleCreated(e);

            //TestForm tsf = new TestForm();
            IntPtr hSysMenu = GetSystemMenu(this.Handle, false);
            AppendMenu(hSysMenu, MF_SEPARATOR, 0, String.Empty);
            AppendMenu(hSysMenu, MF_STRING, SYSMENU_ABOUT_ID, "关于 (&A) ...");
        }

        protected override void WndProc(ref Message m)
        {
            base.WndProc(ref m);

            if ((m.Msg==WM_SYSCOMMAND) && ((int)m.WParam==SYSMENU_ABOUT_ID))
            {
                TestForm testform = new TestForm();
                testform.ShowDialog();
            }
        }

<a href='https://download.csdn.net/download/zxc000/8542729'>https://download.csdn.net/download/zxc000/8542729</a>
<a href='https://blog.csdn.net/DoitPlayer/article/details/72832954'>https://blog.csdn.net/DoitPlayer/article/details/72832954</a>
<a href='https://www.cnblogs.com/liunlls/p/wpf-WindowInteropHelper.html'>https://www.cnblogs.com/liunlls/p/wpf-WindowInteropHelper.html</a>
<a href='https://blog.csdn.net/lucifinil_s/article/details/6384111'>https://blog.csdn.net/lucifinil_s/article/details/6384111</a>