Winforms: Windows 7中Taskbar的新效果（1）——概述

Win7推出之后，很多用户发现Windows的界面漂亮了很多。在这些界面中，Taskbar是最引人注目的一个更新。在最新的Taskbar中，缩略图能显示更加丰富的信息。右键点击Taskbar上的按钮，弹出的菜单提供了很多选项以方便用户的操作。比如右键单击文件管理器Explorer的按钮，就会在弹出的菜单中列出用户最经常浏览的文件夹。
微软在推出新的Taskbar效果的同时，也推出了一系列对应的API。调用这些API，程序员可以开发出具有很酷效果的应用程序。在MSDN中，http://msdn.microsoft.com/en-us/library/dd378460(VS.85).aspx有这些API的详细用法介绍。
到目前为止，Winforms还没有提供对最新的Taskbar的支持。程序员如果想用Winforms开发出具有Win7效果的Taskbar，需要利用.NET提供的InterOp功能。我们用InterOp定义ITaskbarList4如下：
    [ComImportAttribute()]
    [GuidAttribute("c43dc798-95d1-4bea-9030-bb99e2983a1a")]
    [InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
    internal interface ITaskbarList4
    {
        // ITaskbarList
        [PreserveSig]
        void HrInit();
        [PreserveSig]
        void AddTab(IntPtr hwnd);
        [PreserveSig]
        void DeleteTab(IntPtr hwnd);
        [PreserveSig]
        void ActivateTab(IntPtr hwnd);
        [PreserveSig]
        void SetActiveAlt(IntPtr hwnd);
 
        // ITaskbarList2
        [PreserveSig]
        void MarkFullscreenWindow(
            IntPtr hwnd,
            [MarshalAs(UnmanagedType.Bool)] bool fFullscreen);
 
        // ITaskbarList3
        [PreserveSig]
        void SetProgressValue(IntPtr hwnd, UInt64 ullCompleted, UInt64 ullTotal);
        [PreserveSig]
        void SetProgressState(IntPtr hwnd, TBPFLAG tbpFlags);
        [PreserveSig]
        void RegisterTab(IntPtr hwndTab, IntPtr hwndMDI);
        [PreserveSig]
        void UnregisterTab(IntPtr hwndTab);
        [PreserveSig]
        void SetTabOrder(IntPtr hwndTab, IntPtr hwndInsertBefore);
        [PreserveSig]
        void SetTabActive(IntPtr hwndTab, IntPtr hwndInsertBefore, uint dwReserved);
        [PreserveSig]
        HRESULT ThumbBarAddButtons(
            IntPtr hwnd,
            uint cButtons,
            [MarshalAs(UnmanagedType.LPArray)] THUMBBUTTON[] pButtons);
        [PreserveSig]
        HRESULT ThumbBarUpdateButtons(
            IntPtr hwnd,
            uint cButtons,
            [MarshalAs(UnmanagedType.LPArray)] THUMBBUTTON[] pButtons);
        [PreserveSig]
        void ThumbBarSetImageList(IntPtr hwnd, IntPtr himl);
        [PreserveSig]
        void SetOverlayIcon(
          IntPtr hwnd,
          IntPtr hIcon,
          [MarshalAs(UnmanagedType.LPWStr)] string pszDescription);
        [PreserveSig]
        void SetThumbnailTooltip(
            IntPtr hwnd,
            [MarshalAs(UnmanagedType.LPWStr)] string pszTip);
        [PreserveSig]
        void SetThumbnailClip(
            IntPtr hwnd,
            ref RECT prcClip);
 
        // ITaskbarList4
        void SetTabProperties(IntPtr hwndTab, STPFLAG stpFlags);
    }
 
 
    internal enum TBPFLAG
    {
        TBPF_NOPROGRESS = 0,
        TBPF_INDETERMINATE = 0x1,
        TBPF_NORMAL = 0x2,
        TBPF_ERROR = 0x4,
        TBPF_PAUSED = 0x8
    }
 
    internal enum STPFLAG
    {
        STPF_NONE = 0x0,
        STPF_USEAPPTHUMBNAILALWAYS = 0x1,
        STPF_USEAPPTHUMBNAILWHENACTIVE = 0x2,
        STPF_USEAPPPEEKALWAYS = 0x4,
        STPF_USEAPPPEEKWHENACTIVE = 0x8
    }
 
    internal enum THBMASK
    {
        THB_BITMAP = 0x1,
        THB_ICON = 0x2,
        THB_TOOLTIP = 0x4,
        THB_FLAGS = 0x8
    }
 
    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
    internal struct THUMBBUTTON
    {
        /// <summary>
        /// WPARAM value for a THUMBBUTTON being clicked.
        /// </summary>
        internal const int THBN_CLICKED = 0x1800;
 
        [MarshalAs(UnmanagedType.U4)]
        internal THBMASK dwMask;
        internal uint iId;
        internal uint iBitmap;
        internal IntPtr hIcon;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
        internal string szTip;
        [MarshalAs(UnmanagedType.U4)]
        internal THBFLAGS dwFlags;
    }
 
    [Flags]
    internal enum THBFLAGS
    {
        THBF_ENABLED = 0x00000000,
        THBF_DISABLED = 0x00000001,
        THBF_DISMISSONCLICK = 0x00000002,
        THBF_NOBACKGROUND = 0x00000004,
        THBF_HIDDEN = 0x00000008,
        THBF_NONINTERACTIVE = 0x00000010
    }
 
 
另外，我们还需要声明接口ITaskbarList4的一个实现如下：
    [GuidAttribute("56FDF344-FD6D-11d0-958A-006097C9A090")]
    [ClassInterfaceAttribute(ClassInterfaceType.None)]
    [ComImportAttribute()]
    internal class CTaskbarList { }
 
接下来我问定义类TaskbarManager来管理Taskbar，代码如下：
    class TaskbarManager
    {
        // Hide the default constructor
        private TaskbarManager()
        {
 
        }
 
        // Best practice recommends defining a private object to lock on
        private static Object syncLock = new Object();
 
        // Internal implemenation of ITaskbarList4 interface
        private ITaskbarList4 taskbarList;
        internal ITaskbarList4 TaskbarList
        {
            get
            {
                if (taskbarList == null)
                {
                    // Create a new instance of ITaskbarList3
                    lock (syncLock)
                    {
                        if (taskbarList == null)
                        {
                            taskbarList = (ITaskbarList4)new CTaskbarList();
                            taskbarList.HrInit();
                        }
                    }
                }
 
                return taskbarList;
            }
        }
 
        private static volatile TaskbarManager instance;
        /// <summary>
        /// Represents an instance of the Windows Taskbar
        /// </summary>
        public static TaskbarManager Instance
        {
            get
            {
                ThrowIfNotSupport();
 
                if (instance == null)
                {
                    lock (syncLock)
                    {
                        if (instance == null)
                            instance = new TaskbarManager();
                    }
                }
 
                return instance;
            }
        }
 
        public static void ThrowIfNotSupport()
        {
            bool isWin7 = Environment.OSVersion.Version.Major > 6;
            bool isSever2008R2 = Environment.OSVersion.Version.Major == 6
                && Environment.OSVersion.Version.Minor >= 1;
 
            if (!isWin7 && !isSever2008R2)
            {
                throw new PlatformNotSupportedException("Only supported on Windows 7/Sever2008 R2 or newer.");
            }
        }
    }
 
运行ITaskbarList4至少需要Win7或者Server 2008 R2，因此在之前版本的Windows上我们只能抛出异常。
在接下来的几篇博客，我将详细介绍如果调用ITaskbarList4中的接口，实现Taskbar的最新效果。