二、实现原理
Windows文件夹管理树的实现实质上是对Windows名空间（Namespace）的遍历。名空间中每个文件夹都提供了一个IShellFolder接口，遍历名空间的方法是：
1）调用SHGetDesktopFolder函数获得桌面文件夹的IShellFolder接口，桌面文件夹是文件夹管理树的根节点。
2）再调用所获得的IShellFolder接口的EnumObjects成员函数列举出子文件夹。
3）调用IShellFolder的BindToObject成员函数获得子文件夹的IShellFolder接口。
4）重复步骤2）、3）列举出某文件夹下的所有子文件夹，只至所获得的IShellFolder接口为nil为止。
下面解释将要用到的几个主要函数，它们在ShlObj单元中定义：
1）function SHGetDesktopFolder(var ppshf: IShellFolder): HResult;
该函数通过ppshf获得桌面文件夹的IShellFolder接口。
2）function IShellFolder.EnumObjects(hwndOwner: HWND; grfFlags: DWORD;
out EnumIDList: IEnumIDList): HResult;
该函数获得一个IEnumIDList接口，通过调用该接口的Next等函数可以列举出IShellFolder接口所对应的文件夹的内容，内容的类型由grfFlags来指定。我们需要列举出子文件夹来，因此grfFlags的值指定为SHCONTF_FOLDERS。HwndOwner是属主窗口的句柄。
3）function IShellFolder.BindToObject(pidl: PItemIDList; pbcReserved: Pointer;
const riid: TIID; out ppvOut: Pointer): HResult;
该函数获得某个子文件夹的IShellFolder接口，该接口由ppvOut返回。pidl是一个指向元素标识符列表的指针，Windows95/98中用元素标识符和元素标识符列表来标识名空间中的对象，它们分别类似于文件名和路径。需要特别指出的是：pidl作为参数传递给Shell API函数时，必须是相对于桌面文件夹的绝对路径，而传递给IShellFolder接口的成员函数时，则应是相对于该接口所对应文件夹的相对路径。pbcReserved应指定为nil，riid则应指定为IID_IShellFolder。
其它函数可以查阅Delphi提供的《Win32 Programmer's Reference》。
三、程序清单
下面的源代码在Windows98中实现，并在Windows2000测试版中测试无误(程序运行结果如图1所示)，有兴趣的读者可以将其改写成Delphi组件，以备常用。
unit BrowseTreeView;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
ShlObj, ComCtrls;
type
PTreeViewItem = ^TTreeViewItem;
TTreeViewItem = record
ParentFolder: IShellFolder; // 接点对应的文件夹的父文件夹的IShellFolder接口
Pidl, FullPidl: PItemIDList; // 接点对应的文件夹的相对和绝对项目标识符列表
HasExpanded: Boolean; // 接点是否展开
end;
图1 程序运行结果
TForm1 = class(TForm)
TreeView1: TTreeView;
procedure FormDestroy(Sender: TObject);
procedure FormCreate(Sender: TObject);
procedure TreeView1Expanding(Sender: TObject; Node: TTreeNode;
var AllowExpansion: Boolean);
private
FItemList: TList;
procedure SetTreeViewImageList;
procedure FillTreeView(Folder: IShellFolder; FullPIDL: PItemIDList; ParentNode: TTreeNode);
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
uses
ActiveX, ComObj, ShellAPI, CommCtrl;
// 以下是几个对项目标识符进行操作的函数
procedure DisposePIDL(ID: PItemIDList);
var
Malloc: IMalloc;
begin
if ID = nil then Exit;
OLECheck(SHGetMalloc(Malloc));
Malloc.Free(ID);
end;
function CopyItemID(ID: PItemIDList): PItemIDList;
var
Malloc: IMalloc;
begin
Result := nil;
OLECheck(SHGetMalloc(Malloc));
if Assigned(ID) then
begin
Result := Malloc.Alloc(ID^.mkid.cb + sizeof(ID^.mkid.cb));
CopyMemory(Result, ID, ID^.mkid.cb + sizeof(ID^.mkid.cb));
end;
end;
function NextPIDL(ID: PItemIDList): PItemIDList;
begin
Result := ID;
Inc(PChar(Result), ID^.mkid.cb);
end;
function GetPIDLSize(ID: PItemIDList): Integer;
begin
Result := 0;
if Assigned(ID) then
begin
Result := sizeof(ID^.mkid.cb);
while ID^.mkid.cb <> 0 do
begin
Inc(Result, ID^.mkid.cb);
ID := NextPIDL(ID);
end;
end;
end;
function CreatePIDL(Size: Integer): PItemIDList;
var
Malloc: IMalloc;
HR: HResult;
begin
Result := nil;
HR := SHGetMalloc(Malloc);
if Failed(HR) then Exit;
try
Result := Malloc.Alloc(Size);
if Assigned(Result) then
FillChar(Result^, Size, 0);
finally
end;
end;
function ConcatPIDLs(ID1, ID2: PItemIDList): PItemIDList;
var
cb1, cb2: Integer;
begin
if Assigned(ID1) then
cb1 := GetPIDLSize(ID1) - sizeof(ID1^.mkid.cb)
else
cb1 := 0;
cb2 := GetPIDLSize(ID2);
Result := CreatePIDL(cb1 + cb2);
if Assigned(Result) then
begin
if Assigned(ID1) then
CopyMemory(Result, ID1, cb1);
CopyMemory(PChar(Result) + cb1, ID2, cb2);
end;
end;
// 将二进制表示的项目标识符列表转换成有可识的项目名
function GetDisplayName(Folder: IShellFolder; PIDL: PItemIDList;
ForParsing: Boolean): String;
var
StrRet: TStrRet;
P: PChar;
Flags: Integer;
begin
Result := '';
if ForParsing then
Flags := SHGDN_FORPARSING
else
Flags := SHGDN_NORMAL;
Folder.GetDisplayNameOf(PIDL, Flags, StrRet);
case StrRet.uType of
STRRET_CSTR:
SetString(Result, StrRet.cStr, lStrLen(StrRet.cStr));
STRRET_OFFSET:
begin
P := @PIDL.mkid.abID[StrRet.uOffset - sizeof(PIDL.mkid.cb)];
SetString(Result, P, PIDL.mkid.cb - StrRet.uOffset);
end;
STRRET_WSTR:
Result := StrRet.pOleStr;
end;
end;
function GetIcon(PIDL: PItemIDList; Open: Boolean): Integer;
const
IconFlag = SHGFI_PIDL or SHGFI_SYSICONINDEX or SHGFI_SMALLICON;
var
FileInfo: TSHFileInfo;
Flags: Integer;
begin
if Open then
Flags := IconFlag or SHGFI_OPENICON
else
Flags := IconFlag;
SHGetFileInfo(PChar(PIDL), 0, FileInfo, sizeof(TSHFileInfo), Flags);
Result := FileInfo.iIcon;
end;
// 获得每个文件夹在系统中的图标
procedure GetItemIcons(FullPIDL: PItemIDList; TreeNode: TTreeNode);
begin
with TreeNode do
begin
ImageIndex := GetIcon(FullPIDL, False);
SelectedIndex := GetIcon(FullPIDL, True);
end;
end;
// 获得系统的图标列表
procedure TForm1.SetTreeViewImageList;
var
ImageList: THandle;
FileInfo: TSHFileInfo;
begin
ImageList := SHGetFileInfo(PChar('C:/'), 0, FileInfo,
sizeof(TSHFileInfo), SHGFI_SYSICONINDEX or SHGFI_SMALLICON);
if ImageList <> 0 then
TreeView_SetImageList(TreeView1.Handle, ImageList, 0);
end;
// 生成文件夹管理树
procedure TForm1.FillTreeView(Folder: IShellFolder;
FullPIDL: PItemIDList; ParentNode: TTreeNode);
var
TreeViewItem: PTreeViewItem;
EnumIDList: IEnumIDList;
PIDLs, FullItemPIDL: PItemIDList;
NumID: LongWord;
ChildNode: TTreeNode;
Attr: Cardinal;
begin
try
OLECheck(Folder.EnumObjects(Handle, SHCONTF_FOLDERS, EnumIDList));
while EnumIDList.Next(1, PIDLs, NumID) = S_OK do
begin
FullItemPIDL := ConcatPIDLs(FullPIDL, PIDLs);
TreeViewItem := New(PTreeViewItem);
TreeViewItem.ParentFolder := Folder;
TreeViewItem.Pidl := CopyItemID(PIDLs);
TreeViewItem.FullPidl := FullItemPIDL;
TreeViewItem.HasExpanded := False;
FItemList.Add(TreeViewItem);
ChildNode := TreeView1.Items.AddChildObject(ParentNode,
GetDisplayName(Folder, PIDLs, False), TreeViewItem);
GetItemIcons(FullItemPIDL, ChildNode);
Attr := SFGAO_HASSUBFOLDER or SFGAO_FOLDER;
Folder.GetAttributesOf(1, PIDLs, Attr);
if Bool(Attr and (SFGAO_HASSUBFOLDER or SFGAO_FOLDER)) then
if Bool(Attr and SFGAO_FOLDER) then
if Bool(Attr and SFGAO_HASSUBFOLDER) then
ChildNode.HasChildren := True;
end;
except
// 你可在此处对异常进行处理
end;
end;
procedure TForm1.FormDestroy(Sender: TObject);
var
I: Integer;
begin
try
for I := 0 to FItemList.Count-1 do
begin
DisposePIDL(PTreeViewItem(FItemList[i]).PIDL);
DisposePIDL(PTreeViewItem(FItemList[i]).FullPIDL);
end;
FItemList.Clear;
FItemList.Free;
except
end;
end;
procedure TForm1.FormCreate(Sender: TObject);
var
Folder: IShellFolder;
begin
SetTreeViewImageList;
OLECheck(SHGetDesktopFolder(Folder));
FItemList := TList.Create;
FillTreeView(Folder, nil, nil);
end;
procedure TForm1.TreeView1Expanding(Sender: TObject; Node: TTreeNode;
var AllowExpansion: Boolean);
var
TVItem: PTreeViewItem;
SHFolder: IShellFolder;
begin
TVItem := PTreeViewItem(Node.Data);
if TVItem.HasExpanded then Exit;
OLECheck(TVItem.ParentFolder.BindToObject(TVItem^.Pidl,
nil, IID_IShellFolder, Pointer(SHFolder)));
FillTreeView(SHFolder, TVItem^.FullPidl, Node);
Node.AlphaSort;
TVItem^.HasExpanded := True;
end;
end.
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