Today, we’re going to customize the Browse for Folder dialog so it shows only drive letters.<\/p>\n
Start with our previous Browse for Folder customization program<\/a>, and make these changes:<\/p>\n Okay, let’s see what we’ve got.<\/p>\n First, we declare a global variable to remember the location of what was once called My Computer<\/i> but nowadays goes by the name This PC<\/i>. Whatever it is, it’s the thing that contains your drive letters.<\/p>\n The real work happens in the filter. Starting at the bottom, we have a method called The Second, if you pass Okay, working upward, the next method is The first method is First, we say that folders which are ancestors of My Computer<\/i> can show all of their children. This ensures that the Browse for Folder dialog can reach My Computer<\/i> in the first place.<\/p>\n Second, we say that descendants of My Computer<\/i> do not show any children. This is technically redundant because our Finally, if we are showing children of My Computer<\/i> itself, we ask for the parsing name of the item and see if a drive root comes back. If the parsing name is longer than four characters, then the \/\/ Lazy global variable\r\nPIDLIST_ABSOLUTE g_pidlMyComputer;<\/span>\r\n\r\nclass CFunnyFilter :\r\n public RuntimeClass<\r\n RuntimeClassFlags<RuntimeClassType::ClassicCom>,\r\n IFolderFilter>\r\n{\r\npublic:\r\n \/\/ *** IFolderFilter ***\r\n IFACEMETHODIMP ShouldShow(\r\n IShellFolder* psf,\r\n PCIDLIST_ABSOLUTE pidlFolder,\r\n PCUITEMID_CHILD pidlItem)\r\n {\r\n int compare = CompareDepth(pidlFolder);\r\n if (compare < 0) return S_OK;\r\n if (compare > 0) return S_FALSE;\r\n\r\n STRRET str;\r\n psf->GetDisplayNameOf(pidlItem, SHGDN_FORPARSING, &str);\r\n wchar_t buf[4];\r\n if (SUCCEEDED(StrRetToBuf(&str, pidlItem, buf, ARRAYSIZE(buf))) &&\r\n PathIsRoot(buf)) return S_OK;\r\n return S_FALSE;<\/span>\r\n }\r\n\r\n IFACEMETHODIMP GetEnumFlags(\r\n IShellFolder* psf,\r\n PCIDLIST_ABSOLUTE pidlFolder,\r\n HWND *phwnd,\r\n DWORD *pgrfFlags) { \r\n if (CompareDepth(pidlFolder) > 0) *pgrfFlags = 0;<\/span>\r\n return S_OK;\r\n }\r\n\r\nprivate:\r\n static int CompareDepth(PCIDLIST_ABSOLUTE pidl)\r\n {\r\n if (pidl == nullptr) return -1;\r\n if (ILIsEqual(pidl, g_pidlMyComputer)) return 0;\r\n if (ILIsParent(pidl, g_pidlMyComputer, FALSE)) return -1;\r\n return 1;\r\n }<\/span>\r\n};\r\n\r\nint WINAPI WinMain(HINSTANCE hinst, HINSTANCE hinstPrev,\r\n LPSTR lpCmdLine, int nShowCmd)\r\n{\r\n CCoInitialize<\/a> init;\r\n BROWSEINFO bi = { };\r\n TCHAR szDisplayName[MAX_PATH];\r\n SHGetSpecialFolderLocation(nullptr, CSIDL_DRIVES, &g_pidlMyComputer);\r\n bi.pidlRoot = g_pidlMyComputer;<\/span>\r\n bi.pszDisplayName = szDisplayName;\r\n bi.lpfn = BrowseCallbackProc;\r\n bi.ulFlags = BIF_NEWDIALOGSTYLE | BIF_RETURNONLYFSDIRS<\/span>;\r\n PIDLIST_ABSOLUTE pidl = SHBrowseForFolder(&bi);\r\n CoTaskMemFree(pidl);\r\n CoTaskMemFree(g_pidlMyComputer);<\/span>\r\n return 0;\r\n}\r\n<\/pre>\nCheck\u00adDepth<\/code> which determines whether the passed-in folder is an ancestor of, equal to, or a descendant of My Computer<\/i>. Actually, we treat anything that isn’t a parent or equal to My Computer<\/i> as if it were a descendant.<\/p>\nCheck\u00adDepth<\/code> method is method is a bit tricky for a few reasons. First, it treats the null pointer as equivalent to the desktop, so that it is the ancestor of everything. For whatever reason, that’s what IFolder\u00adFilter<\/code> gives you, so we accommodate it.<\/p>\nFALSE<\/code> to ILIs\u00adParent<\/code>, it means that the function will return a nonzero value if the first ID list is an ancestor of or is equal to<\/i> the second ID list. Therefore, we have to do the equality test first.<\/p>\nGet\u00adEnum\u00adFlags<\/code>. This is called when the Browse for Folder dialog wants to enumerate the children of a folder, and it’s our chance to influence what gets enumerated. We don’t want to expand the drives themselves, so if we have something that is a child of My Computer<\/i>, we set the enumeration flags to zero, which means that nothing gets enumerated.<\/p>\nShould\u00adShow<\/code>. This is where most of the excitement is. You are given a folder and an item in that folder, and your job is to decide whether that item should be shown in the Browse for Folder dialog.<\/p>\nGet\u00adEnum\u00adFlags<\/code> prevented those children from being enumerated, but we’ll block them here just to be sure they don’t show up.<\/p>\nStr\u00adRet\u00adTo\u00adBuf<\/code> function will fail with an insufficient-buffer error, in which case we know that we don’t have a drive root.<\/p>\n