How to show the content of a directory in File Explorer as thumbnails?

Question

In a Delphi 10.4.2 win-32 VCL Application in Windows 10, I show the content of a directory in Windows File Explorer using this code and passing a path e.g. C:\MyDirectory\:

procedure ShellOpen(const Url: string; const Params: string = '');
begin
  Winapi.ShellAPI.ShellExecute(0, 'Open', PChar(Url), PChar(Params), nil, SW_SHOWNORMAL);
end;

This works. But how can I force Explorer to show the files in this directory using THUMBNAILS? Are there any parameters for this that I could use in this procedure?

I have searched a lot for this but did not find anything.

Answer 1

You want to use the IFolderView::SetCurrentViewMode method.

Here is a C++ (using Visual Studio's ATL) example:

int main()
{
    CoInitialize(NULL);
    {
        // get a shell item
        CComPtr<IShellItem> folder;
        ATLASSERT(SUCCEEDED(SHCreateItemFromParsingName(L"c:\\myPath1\myPath2", nullptr, IID_PPV_ARGS(&folder))));

        // get its PIDL
        CComHeapPtr<ITEMIDLIST> pidl;
        ATLASSERT(SUCCEEDED(CComQIPtr<IPersistIDList>(folder)->GetIDList(&pidl)));

        // open the item
        SHELLEXECUTEINFO info = { };
        info.cbSize = sizeof(info);
        info.fMask = SEE_MASK_IDLIST;
        info.nShow = SW_SHOW;
        info.lpIDList = pidl;
        ATLASSERT(ShellExecuteEx(&info));

        // build a variant from the PIDL
        UINT size = ILGetSize(pidl);
        SAFEARRAY* psa = SafeArrayCreateVector(VT_UI1, 0, size);
        CopyMemory(psa->pvData, pidl, size);
        CComVariant v;
        v.parray = psa;
        v.vt = VT_ARRAY | VT_UI1;

        // find the opened window
        CComPtr<IShellWindows> windows;
        ATLASSERT(SUCCEEDED(windows.CoCreateInstance(CLSID_ShellWindows)));

        CComVariant empty;
        long hwnd;
        CComPtr<IDispatch> disp;
        do
        {
            windows->FindWindowSW(&v, &empty, SWC_BROWSER, &hwnd, SWFO_NEEDDISPATCH, &disp);
            if (disp)
                break;

            // we sleep for a while but using events would be better
            // see https://stackoverflow.com/a/59974072/403671
            Sleep(500);
        } while (true);

        // get IFolderView
        CComPtr<IFolderView> view;
        ATLASSERT(SUCCEEDED(IUnknown_QueryService(disp, IID_IFolderView, IID_PPV_ARGS(&view))));

        // change view mode
        ATLASSERT(SUCCEEDED(view->SetCurrentViewMode(FOLDERVIEWMODE::FVM_THUMBNAIL)));
    }

    CoUninitialize();
    return 0;
}

Answer 2

Here's a Delphi version of the approach given by Simon Mourier:

uses
  ComObj, ShellAPI, ShlObj, ActiveX, SHDocVw, ShLwApi;

function IUnknown_QueryService(punk: IUnknown; const guidService: TGUID;
  const IID: TGUID; out Obj): HRESULT; stdcall; external 'ShLwApi'
  name 'IUnknown_QueryService';

type
  TFolderViewMode = (fvmAuto, fvmIcon, fvmSmallIcon, fvmList, fvmDetails,
    fvmThumbnail, fvmTile, fvmThumbstrip, fvmContent);

procedure OpenFolder(AHandle: HWND; const AFolder: string; AViewMode: TFolderViewMode);
const
  FolderViewModes: array[TFolderViewMode] of Cardinal =
    (Cardinal(FVM_AUTO), FVM_ICON, FVM_SMALLICON, FVM_LIST, FVM_DETAILS,
     FVM_THUMBNAIL, FVM_TILE, FVM_THUMBSTRIP, FVM_CONTENT);
var
  ShellItem: IShellItem;
  PIDL: PItemIDList;
  SEInfo: TShellExecuteInfo;
  ILSize: Cardinal;
  SafeArray: PSafeArray;
  v: OleVariant;
  ShellWindows: IShellWindows;
  ExplorerHWND: Integer;
  disp: IDispatch;
  view: IFolderView;
  dummy: OleVariant;
begin

  OleCheck(CoInitialize(nil));
  try

    OleCheck(SHCreateItemFromParsingName(PChar(AFolder), nil, IShellItem, ShellItem));
    try

      OleCheck((ShellItem as IPersistIDList).GetIDList(PIDL));
      try

        ZeroMemory(@SEInfo, SizeOf(SEInfo));
        SEInfo.cbSize := SizeOf(SEInfo);
        SEInfo.Wnd := AHandle;
        SEInfo.fMask := SEE_MASK_IDLIST;
        SEInfo.nShow := SW_SHOW;
        SEInfo.lpIDList := PIDL;
        Win32Check(ShellExecuteEx(@SEInfo));

        ILSize := ILGetSize(PIDL);
        SafeArray := SafeArrayCreateVector(VT_UI1, 0, ILSize);

        CopyMemory(SafeArray.pvData, PIDL, ILSize);
        PVariantArg(@v).vt := VT_ARRAY or VT_UI1;
        PVariantArg(@v).parray := SafeArray;

        OleCheck(CoCreateInstance(CLASS_ShellWindows, nil, CLSCTX_LOCAL_SERVER,
          IShellWindows, ShellWindows));
        try
          dummy := Unassigned;
          var c: Integer := 0;
          repeat
            if c > 0 then
              Sleep(200);
            disp := ShellWindows.FindWindowSW(v, dummy, SWC_BROWSER, ExplorerHWND,
              SWFO_NEEDDISPATCH);
            Inc(c);
          until Assigned(disp) or (c > 15);
          if disp = nil then
            Exit;
          OleCheck(IUnknown_QueryService(disp, IFolderView, IFolderView, view));
          try
            OleCheck(view.SetCurrentViewMode(FolderViewModes[AViewMode]));
          finally
            view := nil;
          end;
        finally
          ShellWindows := nil;
        end;

      finally
        CoTaskMemFree(PIDL);
      end;

    finally
      ShellItem := nil;
    end;

  finally
    CoUninitialize;
  end;

end;

Instead of sleep-polling indefinitely for the window (and potentially killing the application!), I give up after 3 seconds.

Example usage:

procedure TForm1.Button1Click(Sender: TObject);
begin
  OpenFolder(Handle, 'C:\Users\Andreas Rejbrand\Skrivbord\Test', fvmThumbnail);
end;

The view modes,

type
  TFolderViewMode = (fvmAuto, fvmIcon, fvmSmallIcon, fvmList, fvmDetails,
    fvmThumbnail, fvmTile, fvmThumbstrip, fvmContent);

are mapped directly to Windows' FOLDERVIEWMODEs. Please note that your version of Windows might not support all of them.

Answer 3

No, EXPLORER.EXE has no parameter for this - it neither had one in Windows 7, nor does it have one in Windows 10. There are surprisingly few parameters available anyway.

Your best bet is starting the Explorer thru CreateProcessW() to then obtain the handle of its main thread and finally find the new window. Then you can manipulate individual controls, such as the file list. See this answer, based on AutoIt: Automating Windows Explorer - it basically uses IShellBrowser and (beyond Windows XP) IFolderView2.SetViewModeAndIconSize() to then apply FVM_THUMBNAIL.