How to Read/Write Windows 7 Library Locations?

Question

Intro

In Windows 7 you have some special folders for documents, pictures and music etc called Libraries.

If you are not aware of them, basic

Answer 1

Use one of the SHLoadLibraryFrom...() functions, like SHLoadLibraryFromKnownFolder(), to get an IShellLibrary interface, then you can use its methods to enumerate and manipulate the Library, such as IShellLibrary::GetFolders(), IShellLibrary::AddFolder(), IShellLibrary::RemoveFolder(), etc.

Update: For example:

uses
  ..., ActiveX, KnownFolders, ShlObj;

// The SHLoadLibraryFrom...() functions are implemented inline in the Win32 SDK
// shobjidl.h header file, so you have to implement them manually in your 
// code if you you are not using a version of Delphi that already implements
// them in the RTL's ShlObj.pas unit for you...

// SHLoadLibraryFromKnownFolder() is defined wrong in ShlObj.pas!!! See QC #109306
function My_SHLoadLibraryFromKnownFolder(const kfidLibrary: TGUID; grfMode: DWORD; riid: TIID; out ppv): HRESULT;
var
  plib: IShellLibrary;
begin
  Result := CoCreateInstance(CLSID_ShellLibrary, nil, CLSCTX_INPROC_SERVER, IShellLibrary, plib);
  if SUCCEEDED(Result) then
  begin
    Result := plib.LoadLibraryFromKnownFolder(kfidLibrary, grfMode);
    if SUCCEEDED(Result) then
      Result := plib.QueryInterface(riid, ppv);
  end;
end;

function GetLibraryFileSystemFolders(FolderID: TGUID; Folders: TStrings): Boolean;
var
  SL: IShellLibrary;
  Arr: IShellItemArray;
  Enum: IEnumShellItems;
  Item: IShellItem;
  Path: LPWSTR;
begin
  Result := False;

  if FAILED(My_SHLoadLibraryFromKnownFolder(FolderID, STGM_READ, IShellLibrary, SL)) then
    Exit;

  if FAILED(SL.GetFolders(LFF_FORCEFILESYSTEM, IShellItemArray, Arr)) then
    Exit;

  if FAILED(Arr.EnumItems(Enum)) then
    Exit;

  while Enum.Next(1, Item, nil) = S_OK then
  begin
    if FAILED(Item.GetDisplayName(SIGDN_FILESYSPATH, Path)) then
      Exit;
    try
      Folders.Add(Path);
    finally
      CoTaskMemFree(Path); 
    end;
    Item := nil;
  end;

  Result := True;
end;

.

var
  Folders: TStringList;
begin
  Folders := TStringList.Create;
  try
    if GetLibraryFileSystemFolders(FOLDERID_DocumentsLibrary, Folders) then
    begin
      //...
    end;
  finally
    Folders.Free;
  end;
end;

Update: SHLoadLibraryFromKnownFolder() only works for Microsoft-defined Libraries that have KNOWNFOLDERID values defined. If you want to access custom Libraries, you have to use a slightly modified approach to obtaining the IShellLibrary interface, eg:

// SHLoadLibraryFromItem() is defined wrong in ShlObj.pas!!! See QC #109306
function My_SHLoadLibraryFromItem(const psiLibrary: IShellItem; grfMode: DWORD; const riid: TIID; out ppv): HResult;
var
  plib: IShellLibrary;
begin
  Result := CoCreateInstance(CLSID_ShellLibrary, nil, CLSCTX_INPROC_SERVER, IID_IShellLibrary, plib);
  if Succeeded(Result) then
  begin
    Result := plib.LoadLibraryFromItem(psiLibrary, grfMode);
    if Succeeded(Result) then
      Result := plib.QueryInterface(riid, ppv);
  end;
end;

function GetShellLibraryforLibrary(const LibraryName: String; grfMode: DWORD; var ppv: IShellLibrary): Boolean;
var
  SL: IShellLibrary;
  Enum: IEnumShellItems;
  Item: IShellItem;
  DisplayName: LPWSTR;
  hr: HRESULT;
begin
  Result := False;
  ppv := nil;

  if FAILED(SHGetKnownFolderItem(FOLDERID_Libraries, 0, 0, IShellItem, PPointer(@Item)^) then
    Exit;

  hr := Item.BindToHandler(nil, BHID_EnumItems, IEnumShellItems, Enum);
  if FAILED(hr) then
    Exit;

  Item := nil;
  while Enum.Next(1, Item, nil) = S_OK do
  begin
    if FAILED(Item.GetDisplayName(SIGDN_NORMALDISPLAY, DisplayName)) then
      Exit;
    try
      if AnsiSameText(DisplayName, LibraryName) then
      begin
        Result := SUCCEEDED(My_SHLoadLibraryFromItem(Item, grfMode, IShellLibrary, ppv));
        Break;
      end;
    finally
      CoTaskMemFree(DisplayName);
    end;
    Item := nil;
  end;
end;

function GetLibraryFileSystemFolders(const LibraryName: String; Folders: TStrings): Boolean;
var
  SL: IShellLibrary;
  Arr: IShellItemArray;
  Enum: IEnumShellItems;
  Item: IShellItem;
  Path: LPWSTR;
begin
  Result := False;

  if not GetShellLibraryforLibrary(LibraryName, STGM_READ, SL) then
    Exit;

  if FAILED(SL.GetFolders(LFF_FORCEFILESYSTEM, IShellItemArray, Arr)) then
    Exit;

  if FAILED(Arr.EnumItems(Enum)) then
    Exit;

  while Enum.Next(1, Item, nil) = S_OK then
  begin
    if FAILED(Item.GetDisplayName(SIGDN_FILESYSPATH, Path)) then
      Exit;
    try
      Folders.Add(Path);
    finally
      CoTaskMemFree(Path); 
    end;
    Item := nil;
  end;

  Result := True;
end;

.

var
  Folders: TStringList;
begin
  Folders := TStringList.Create;
  try
    if GetLibraryFileSystemFolders('MyLibrary', Folders) then
    begin
      //...
    end;
  finally
    Folders.Free;
  end;
end;