第二部分 Windows SHELL编程
There are many types of shell extensions, each type being invoked when different events happen. Here are a few of the more common types, and the situations in which they are invoked:[7]
| Type | When it's invoked | What it does |
| Context menu handler | User right-clicks on a file or folder. In shell versions 4.71+, also invoked on a right-click in the background of a directory window. | Adds items to the context menu. |
| Property sheet handler | Properties dialog displayed for a file. | Adds pages to the property sheet. |
| Drag and drop handler | User right-drags items and drops them on a directory window or the desktop. | Adds items to the context menu. |
| Drop handler | User drags items and drops them on a file. | Any desired action. |
| QueryInfo handler (shell version 4.71+) | User hovers the mouse over a file or other shell object like My Computer. | Returns a string that Explorer displays in a tooltip. |
Before we begin coding, there are some tips that will make the job easier. When you cause a shell extension to be loaded by Explorer, it will stay in memory for a while, making it impossible to rebuild the DLL.
To have Explorer unload extensions more often, create this registry key:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\AlwaysUnloadDLL
and set the default value to "1". On 9x, that's the best you can do. On NT, go to this key:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer and create a DWORD called DesktopProcess with a value of 1. This makes the desktop and Taskbar run in one process,
and subsequent Explorer windows each run in its own process. This means that you can do your debugging with a single Explorer window, and when you close it, your DLL is automatically unloaded, avoiding
any problems with the file being in use. You will need to log off and back on for these changes to take effect.[7]
第一：注册表编程。第二：Shell Extension COM编程。通过注册表方式实现
其实十分简单，请参阅 COM[1]组件注册表实现。在以下的内容为 shell 扩展编程---" Context Menu 处理器。
Shell扩展实例均为进程内组件，它们均以动态库的形式存在。
When our shell extension is loaded, Explorer calls our QueryInterface() function to get a pointer to an IShellExtInit interface.[7]
IShellExtInit接口：IShellExtInit 接口为 Shell 扩展编程必须要实现的接口。该接口主要用来初始化 Shell 扩展处理器，它仅有一个虚成员函数Initialize，用户所有的 Shell 扩展初始化动作都由该函数完成。
在 Initialize 函数中，我们要做的事情就是获取用户鼠标右键点击的文件名称。当用户在一个拥有WS_EX_ACCEPTFILES风格的窗体中Drag/Drop文件时这些文件名会以同一种格式存储，而且文件完整路径的获取也都以DragQueryFile API函数来实现。但是DragQueryFile需要传入一个HDROP句柄，该句柄即为Drag/Drop文件名称列表数据句柄(开始存放数据的内存区域首指针)。而 HDROP句柄的可以通过接口"DATAOBJECT lpdobj"的成员函数"GetData"来获取。
进程内组件编程的一些特点，大体总结如下："新建自己的接口，然后继承某些接口，最后一一实现这些接口的所有虚成员函数或加入自己的成员函数，最后就是组件的注册"。
1) 初始化接口
int Initialize(IntPtr pidlFolder, IntPtr lpdobj, uint hKeyProgID);
HRESULT IShellExtInit::Initialize (
LPCITEMIDLIST pidlFolder,
LPDATAOBJECT pDataObj,
HKEY hProgID )
Explorer 使用该方法传递给我们各种各样的信息.
Explorer uses this method to give us various information. pidlFolder is the PIDL of the folder containing the files being acted upon. (A PIDL [pointer to an ID
list] is a data structure that uniquely identifies any object in the shell, whether it's a file system object or not.) pDataObj is an IDataObject interface
pointer through which we retrieve the names of the files being acted upon. hProgID is an open HKEY which we can use to access the registry key containing
our DLL's registration data. For this simple extension, we'll only need to use the pDataObj parameter.[7]
pidlFolder 是用户所选择操作的文件所在的文件夹的PIDL变量(一个PIDL[指向ID列表的指针],是一个数据结构，它唯一地标识了在Shell命名空间的任何对象,一个Shell命名空间中的对象可以是也可以不是真实的文件系统中的对象。)lpdobj是一个IDataObject接口指针，通过它我们可以获取用户所选择操作的文件名。hKeyProgID是一个HKEY注册表键变量，可以用它获取我们的DLL的注册数据。
因此我们可以在这个方法中，获取到被右击选择的一个或多个文件/文件夹名。
The COM_MAP is how ATL implements QueryInterface(). It tells ATL what interfaces other programs can retrieve from our COM objects.[7]
2) 与上下文菜单交互的接口
Once Explorer has initialized our extension, it will call the IContextMenu methods to let us add menu items, provide fly-by help, and carry out the user's selection.[7]
一旦 Explorer 初始化了扩展,它就会接着调用 IContextMenu 的方法让我们添加菜单项, 提供状态栏上的提示, 并响应执行用户的选择。
处理器类型 COM接口
Context menu 处理器 IContextMenu
Property sheet 处理器 IShellPropSheetExt
Drag and drop 处理器 IContextMenu
Drop 处理器 IDropTarget
QueryInfo 处理器(Shell V4.71+) IQueryInfo
其中的"Drag and drop 处理器"除了COM接口IContextMenu需要实现外还得需要注册表的特殊注册才行。IContextMenu 接口有三个虚成员函数需要我们的组件来实现：
The first one, QueryContextMenu(), lets us modify the menu.[7]
QueryContextMenu，在QueryContextMenu 成员函数中我们可以加入自己的菜单项，通过 InsertMenu API 函数来实现。
HRESULT IContextMenu::QueryContextMenu (
HMENU hmenu, UINT uMenuIndex, UINT uidFirstCmd,
UINT uidLastCmd, UINT uFlags );
hmenu is a handle to the context menu. uMenuIndex is the position in which we should start adding our items. uidFirstCmd and uidLastCmd are the range of
command ID values we can use for our menu items. uFlags indicates why Explorer is calling QueryContextMenu(), and I'll get to this later.[7]
3) 在状态栏上显示提示帮助
The next IContextMenu that can be called is GetCommandString(). If the user right-clicks a text file in an Explorer window, or selects a text file and then clicks the File menu, the status bar will show fly-by help when our menu item is highlighted. Our GetCommandString() function will return the string that we want Explorer to show.
GetCommandString，GetCommandString 成员函数为 Explorer 提供了在状态栏显示菜单命令提示信息的方法。在这个方法中 "LPSTR pszName" 是我们要关注的参数，我们只要根据 "UINT uFlags" 参数来填充 "LPSTR pszName" 参数即可。在COM 编程中尽可能使用兼容的 TCHAR 类型，也尽量不要使用C类函数库，因为这样会使您无法通过 "Win32 Release Mindependency " 或其他 UINCode/Release 版本的编译过程。
HRESULT IContextMenu::GetCommandString (
UINT idCmd, UINT uFlags, UINT* pwReserved,
LPSTR pszName, UINT cchMax );
idCmd is a zero-based counter that indicates which menu item is selected. Since we have just one menu item, idCmd will always be zero. But if we had added, say, 3 menu items,
idCmd could be 0, 1, or 2. uFlags is another group of flags, We can ignore pwReserved. pszName is a pointer to a buffer owned by the shell where we will store
the help string to be displayed. cchMax is the size of the buffer. The return value is one of the usual HRESULT constants, such as S_OK or E_FAIL.[7]
GetCommandString() can also be called to retrieve a "verb" for a menu item. A verb is a language-independent string that identifies an action that can be taken on a file. The docs for ShellExecute() have more to say, and the subject of verbs is best suited for another article, but the short version is that verbs can be either listed in the registry
(such as "open" and "print"), or created dynamically by context menu extensions. This lets an action implemented in a shell extension be invoked by a call to ShellExecute().
Anyway, the reason I mentioned all that is we have to determine why GetCommandString() is being called. If Explorer wants a fly-by help string, we provide it. If Explorer is asking for a verb, we'll just ignore the request. This is where the uFlags parameter comes into play. If uFlags
has the GCS_HELPTEXT bit set, then Explorer is asking for fly-by help. Additionally, if the GCS_UNICODE bit is set, we must return a Unicode string.[7]
下一个要被调用的IContextMenu 方法是 GetCommandString().。如果用户是在浏览器窗口中右击文本文件，或选中一个文本文件后单击文件菜单时,状态栏会显示提示帮助。我们的 GetCommandString() 函数将返回一个帮助字符串供浏览器显示。
4）执行用户的选择
InvokeCommand，实现最终菜单项命令的执行。
This method is called if the user clicks on the menu item we added. The prototype for InvokeCommand() is:
HRESULT IContextMenu::InvokeCommand (
LPCMINVOKECOMMANDINFO pCmdInfo );
IContextMenu 接口的最后一个方法是 InvokeCommand()。当用户点击我们添加的菜单项时该方法将被调用。其参数：CMINVOKECOMMANDINFO 结构带有大量的信息, 但我们只关心 lpVerb 和 hwnd 这两个成员。
lpVerb performs double duty - it can be either the name of the verb that was invoked, or it can be an index telling us which of our menu items was clicked on. hwnd is the handle of the Explorer
window where the user invoked our extension; we can use this window as the parent window for any UI that we show.[7]
lpVerb参数有两个作用------它或是可被激发的verb(动作)名,或是被点击的菜单项的索引值。hwnd 是用户激活我们的菜单扩展时所在的浏览器窗口的句柄。我们可以根据被点击的菜单项索引，来执行相应的操作。
5）注册Shell扩展
现在我们已经实现了所有需要的COM接口. 可是我们怎样才能让浏览器使用我们的扩展呢？首先，我们要注册动态库。但仅仅这样是不够的，为了告诉浏览器使用我们的扩展, 我们需要在文本文件类型(因为我们要关联文本)的注册表键下注册扩展。ATL automatically generates code that registers our DLL as a COM server, but that just lets other apps use our DLL. In order to tell Explorer our extension exists, we need to register it under the key that holds info about text files。[7]
The NoRemove keyword means that the key should not be deleted when the server is unregistered,ForceRemove, which means that if the key exists, it will be deleted
before the new key is written.