shell - 从 Explorer Shell 拖放到 Virtual TreeView 时如何更改放置提示(Delphi 应用程序)？

Question

以下是从 Windows Shell 接受文件到 Virtual TreeView 的方法:How do you drag and drop a file from Explorer Shell into a VirtualTreeView control in a Delphi application?

这是我在 OnDragOver 中为 Effect 参数设置 DROPEFFECT_LINK 时的样子:

问题是:是否有可能更改提示文本 说“链接到某物”？

我认为答案与 IDragSourceHelper2::SetFlags(_DROPDESCRIPTION 记录)有关，但我不确定我是否可以使用它以及在哪里使用它。

Answer 1

很快:
将 IDataObject.SetData 与 FormatEtc.cfFormat=RegisterClipboardFormat(CFSTR_DROPDESCRIPTION) 一起使用和 DROPDESCRIPTION 结构作为 TStgMedium 内容。

拖动源应在 IDragSourceHelper.InitializeFromBitmap 或 IDragSourceHelper.InitializeFromWindow 之前调用 IDragSourceHelper2.SetFlags(DSH_ALLOWDROPDESCRIPTIONTEXT)。 VirtualTreeView 在用作拖动源时自动设置此标志。

---

首先，注册特殊的剪贴板格式。

constructor TForm12.Create(AOwner: TComponent);
begin
  inherited;
  FDragDescriptionFormat := RegisterClipboardFormat(PChar(CFSTR_DROPDESCRIPTION));
end;

接下来，创建方法来为 IDataObject 设置提示:

procedure TForm12.SetDragHint(DataObject: IDataObject; const Value: string; Effect: Integer);
var
  FormatEtc: TFormatEtc;
  Medium: TStgMedium;
  Data: Pointer;
  Descr: DROPDESCRIPTION;
  s: WideString;
begin
  ZeroMemory(@Descr, SizeOf(DROPDESCRIPTION));
  {Do not set Descr.&type to DROPIMAGE_INVALID - this value ignore any custom hint}
  {use same image as dropeffect type}
  Descr.&type := DROPIMAGE_LABEL;
  case Effect of
    DROPEFFECT_NONE:
      Descr.&type := DROPIMAGE_NONE;
    DROPEFFECT_COPY:
      Descr.&type := DROPIMAGE_COPY;
    DROPEFFECT_MOVE:
      Descr.&type := DROPIMAGE_MOVE;
    DROPEFFECT_LINK:
      Descr.&type := DROPIMAGE_LINK;
  end;
  {format message for system}
  if Length(Value) <= MAX_PATH then
  begin
    Move(Value[1], Descr.szMessage[0], Length(Value) * SizeOf(WideChar));
    Descr.szInsert := '';
  end
  else
  begin
    s := Copy(Value, 1, MAX_PATH - 2) + '%1';
    Move(s[1], Descr.szMessage[0], Length(s) * SizeOf(WideChar));

    s := Copy(Value, MAX_PATH - 1, MAX_PATH);
    Move(s[1], Descr.szInsert[0], Length(s) * SizeOf(WideChar));
  end;
  {prepare structures to set DROPDESCRIPTION data} 
  FormatEtc.cfFormat := FDragDescriptionFormat; {registered clipboard format}
  FormatEtc.ptd := nil;
  FormatEtc.dwAspect := DVASPECT_CONTENT;
  FormatEtc.lindex := -1;
  FormatEtc.tymed := TYMED_HGLOBAL;

  ZeroMemory(@Medium, SizeOf(TStgMedium));
  Medium.tymed := TYMED_HGLOBAL;
  Medium.HGlobal := GlobalAlloc(GHND or GMEM_SHARE, SizeOf(DROPDESCRIPTION));
  Data := GlobalLock(Medium.HGlobal);
  Move(Descr, Data^, SizeOf(DROPDESCRIPTION));
  GlobalUnlock(Medium.HGlobal);

  DataObject.SetData(FormatEtc, Medium, True);
end;

最后 - 使用 SetDragHint，例如 - 在 VirtualTreeView.OnDragOver 事件中:

procedure TForm12.vt1DragOver(Sender: TBaseVirtualTree; Source: TObject; Shift: TShiftState; State: TDragState;
  Pt: TPoint; Mode: TDropMode; var Effect: Integer; var Accept: Boolean);
begin
  Accept := True;
  Effect := DROPEFFECT_LINK;
  if State = dsDragMove then
  begin
    SetDragHint(vt1.DragManager.DataObject, Format('Point: (%d, %d)', [Pt.X, Pt.Y]), Effect);
  end
  else
  begin
    Accept := False;
    Effect := DROPEFFECT_NONE;
    SetDragHint(vt1.DragManager.DataObject, '', Effect);
  end;
end;

结果(将文件从 Explorer 拖到 VirtualStringTree):