已经设置了全局Hook，为什么还是只能在主程序中响应消息

[cyh706510441]

写了一个程序，功能为：在桌面双击鼠标左键，显示/隐藏桌面图标。
做法：设置了全局的Hook，判断WM_LBUTTONDBLCLK消息，显示/隐藏图标。在测试程序（mfc，dlg）中加载了这个dll，但只能在对话框中双击能实现功能，在桌面双击，不响应。不知道错误在哪里。。下面是dll中的代码：

#include "stdafx.h"
#include "DesktopHook.h"

#pragma data_seg("MySection")
HHOOK g_hMsgHook = NULL;
HWND g_hDesktopWnd = NULL;
BOOL g_bShow = TRUE;
#pragma data_seg()
#pragma comment(linker, "/section:MySection,RWS")

HWND FindDesktopWindow()
{
	HWND ParentWnd;
	HWND ViewWnd = NULL;
	HWND DesktopWnd;
	ParentWnd = ::FindWindowEx(0, 0, L"WorkerW", L"");  // 获得第一个WorkerW类的窗口
	while ((!ViewWnd) && ParentWnd)
	{
		ViewWnd = ::FindWindowEx(ParentWnd, 0, L"SHELLDLL_DefView", 0);
		ParentWnd = ::FindWindowEx(0, ParentWnd, L"WorkerW", L"");  // until找到正确的WorderW类
	}

	// 如果失败，尝试在Program Manager下搜索
	if (ViewWnd == NULL)
	{
		ParentWnd = ::FindWindow(L"Progman", L"Program Manager");
		ViewWnd = ::FindWindowEx(ParentWnd, 0, L"SHELLDLL_DefView", 0);
	}
	DesktopWnd = ::FindWindowEx(ViewWnd, 0, L"SysListView32", L"FolderView");

	return DesktopWnd;
}

LRESULT CALLBACK GetMsgProc(int code, WPARAM wParam, LPARAM lParam)
{
	MSG* pMsg = (MSG*)lParam;
	switch (pMsg->message)
	{
	case WM_LBUTTONDBLCLK:
		g_bShow = !g_bShow;
		::ShowWindow(g_hDesktopWnd, g_bShow ? SW_SHOW : SW_HIDE);
		break;
	default:
		break;
	}
	return ::CallNextHookEx(g_hMsgHook, code, wParam, lParam);
}


void SetDesktopHook()
{
	// Get desktop hwnd
	g_hDesktopWnd = FindDesktopWindow();

	// Hook post message
	g_hMsgHook = ::SetWindowsHookEx(WH_GETMESSAGE, GetMsgProc, GetModuleHandle(L"DesktopHook"), 0);
}

void FreeDesktopHook()
{
	::UnhookWindowsHookEx(g_hMsgHook);
}