按照 Abdullah 的建议,您可以通过创建自定义组件来实现此目的。通常创建自定义组件的说明在此处。我建议将它安装在 Tool Palette 上的 Standard 中,因为那是 TTreeView 所在的位置。
此处称为 TMyTreeView 的自定义组件在标题中特别包含以下内容:
class PACKAGE TMyTreeView : public TTreeView
{
private:
bool IsAncestor (TTreeViewItem* oItem, TTreeViewItem* oTargetItem);
protected:
int DragDelta;
void StartDrag ();
void __fastcall DragDrop (const Fmx::Types::TDragObject &Data, const System::Types::TPointF &Point);
void __fastcall MouseDown (System::Uitypes::TMouseButton Button, System::Classes::TShiftState Shift, float X, float Y);
void __fastcall MouseMove (System::Classes::TShiftState Shift, float X, float Y);
public:
__fastcall TMyTreeView(TComponent* Owner);
__fastcall ~TMyTreeView ();
TBitmap* DragBmp;
TPointF MouseDownPoint;
TTreeViewItem* DragStartItem;
__published:
};
//---------------------------------------------------------------------------
其中函数在对应的cpp文件中如下:
__fastcall TMyTreeView::TMyTreeView(TComponent* Owner)
: TTreeView(Owner)
{
DragBmp = NULL;
DragStartItem = NULL;
DragDelta = 5;
}
//---------------------------------------------------------------------------
__fastcall TMyTreeView::~TMyTreeView ()
{
if (DragBmp)
delete DragBmp;
}
//---------------------------------------------------------------------------
void __fastcall TMyTreeView::MouseMove (System::Classes::TShiftState Shift, float X, float Y)
{
TTreeView::MouseMove (Shift, X, Y);
if ((abs (X-MouseDownPoint.X) > DragDelta) || (abs (Y-MouseDownPoint.Y) > DragDelta))
StartDrag ();
}
//---------------------------------------------------------------------------
void TMyTreeView::StartDrag ()
{
if (!AllowDrag)
return;
if (!DragStartItem)
return;
if (DragBmp)
delete DragBmp;
_di_IFMXDragDropService service;
if ((TPlatformServices::Current->SupportsPlatformService (__uuidof(IFMXDragDropService)) &&
(service = TPlatformServices::Current->GetPlatformService (__uuidof(IFMXDragDropService)))))
{
TDragObject dragData;
if (!DragStartItem)
return;
dragData.Source = DragStartItem;
DragBmp = DragStartItem->MakeScreenshot ();
dragData.Data = DragBmp;
service->BeginDragDrop ((TForm*)this->Owner, dragData, DragBmp);
DragStartItem = NULL;
}
}
//---------------------------------------------------------------------------
void __fastcall TMyTreeView::MouseDown (System::Uitypes::TMouseButton Button, System::Classes::TShiftState Shift, float X, float Y)
{
TTreeView::MouseDown (Button, Shift, X, Y);
if (AllowDrag)
{
DragStartItem = ItemByPoint (X, Y);
MouseDownPoint.X = X;
MouseDownPoint.Y = Y;
}
else
DragStartItem = NULL;
}
//---------------------------------------------------------------------------
void __fastcall TMyTreeView::DragDrop (const Fmx::Types::TDragObject &Data, const System::Types::TPointF &Point)
{
TTreeViewItem* item = ItemByPoint (Point.X, Point.Y);
if (!item)
return;
TTreeViewItem* srcItem = (TTreeViewItem*)Data.Source;
if (!srcItem)
return;
if (IsAncestor (srcItem, item))
return;
if (item->ParentItem ())
item->ParentItem ()->InsertObject (item->Index, srcItem);
else
this->InsertObject (item->Index, srcItem);
//TTreeView::DragDrop (Data, Point);
}
//---------------------------------------------------------------------------
bool TMyTreeView::IsAncestor (TTreeViewItem* oItem, TTreeViewItem* oTargetItem)
{
for (int i=0; i<oItem->Count; i++)
{
TTreeViewItem* item = oItem->Items [i];
if (item == oTargetItem)
return true;
if (IsAncestor (item, oTargetItem))
return true;
}
return false;
}
//---------------------------------------------------------------------------
将自定义组件安装到工具面板后,您可以像添加任何其他组件一样将其添加到表单中。
特别感谢 Mike Sutton,他有代码可以在此处修改早期版本的 TTreeView 。
添加到窗体后,将 TMyTreeView 控件的 AllowDrag 设置为 true。