[TD]add extensions for drag and drop

src/Mod/TechDraw/App/DrawPage.cpp

@@ -470,6 +470,19 @@ bool DrawPage::canUpdate() const
     return result;
 }
 
+//true if object belongs to this page
+bool DrawPage::hasObject(App::DocumentObject* obj)
+{
+    for (auto& outObj : getOutList()) {
+        //TODO: check if pointer comparision is reliable enough
+        if (outObj == obj) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 //allow/prevent drawing updates for all Pages
 bool DrawPage::GlobalUpdateDrawings(void)
 {

src/Mod/TechDraw/App/DrawPage.h

@@ -107,6 +107,8 @@ public:
 
     bool canUpdate() const;
 
+    bool hasObject(App::DocumentObject* obj);
+
 protected:
     void onBeforeChange(const App::Property* prop) override;
     void onChanged(const App::Property* prop) override;

src/Mod/TechDraw/Gui/AppTechDrawGui.cpp

@@ -61,6 +61,9 @@
 #include "ViewProviderViewPart.h"
 #include "ViewProviderViewSection.h"
 #include "ViewProviderWeld.h"
+#include "ViewProviderPageExtension.h"
+#include "ViewProviderDrawingViewExtension.h"
+#include "ViewProviderTemplateExtension.h"
 #include "Workbench.h"
 
 
@@ -149,6 +152,11 @@ PyMOD_INIT_FUNC(TechDrawGui)
     TechDrawGui::ViewProviderTile::init();
     TechDrawGui::ViewProviderWeld::init();
 
+    TechDrawGui::ViewProviderPageExtension   ::init();
+//    TechDrawGui::ViewProviderPageExtensionPython::init();
+    TechDrawGui::ViewProviderDrawingViewExtension::init();
+    TechDrawGui::ViewProviderTemplateExtension::init();
+
     TechDrawGui::ViewProviderCosmeticExtension::init();
 
     // register preferences pages

src/Mod/TechDraw/Gui/CMakeLists.txt

@@ -351,12 +351,18 @@ SET(TechDrawGuiNav_SRCS
 SET(TechDrawGuiViewProvider_SRCS
     ViewProviderPage.cpp
     ViewProviderPage.h
+    ViewProviderPageExtension.cpp
+    ViewProviderPageExtension.h
     ViewProviderDrawingView.cpp
     ViewProviderDrawingView.h
+    ViewProviderDrawingViewExtension.cpp
+    ViewProviderDrawingViewExtension.h
     ViewProviderProjGroupItem.cpp
     ViewProviderProjGroupItem.h
     ViewProviderTemplate.cpp
     ViewProviderTemplate.h
+    ViewProviderTemplateExtension.cpp
+    ViewProviderTemplateExtension.h
     ViewProviderDimension.cpp
     ViewProviderDimension.h
     ViewProviderBalloon.cpp

src/Mod/TechDraw/Gui/ViewProviderDrawingView.cpp

@@ -42,6 +42,7 @@
 #include <Mod/TechDraw/App/DrawView.h>
 
 #include "ViewProviderDrawingView.h"
+#include "ViewProviderDrawingViewExtension.h"
 #include "MDIViewPage.h"
 #include "QGIView.h"
 #include "QGSPage.h"
@@ -52,9 +53,12 @@ namespace bp = boost::placeholders;
 
 PROPERTY_SOURCE(TechDrawGui::ViewProviderDrawingView, Gui::ViewProviderDocumentObject)
 
-ViewProviderDrawingView::ViewProviderDrawingView()
+ViewProviderDrawingView::ViewProviderDrawingView() :
+    m_myName(std::string())
 {
 //    Base::Console().Message("VPDV::VPDV\n");
+    initExtension(this);
+
     sPixmap = "TechDraw_TreeView";
     static const char *group = "Base";
 
@@ -79,6 +83,7 @@ void ViewProviderDrawingView::attach(App::DocumentObject *pcFeat)
     auto bndProgressMessage = boost::bind(&ViewProviderDrawingView::onProgressMessage, this, bp::_1, bp::_2, bp::_3);
     auto feature = getViewObject();
     if (feature) {
+        m_myName = feature->getNameInDocument();
         connectGuiRepaint = feature->signalGuiPaint.connect(bnd);
         connectProgressMessage = feature->signalProgressMessage.connect(bndProgressMessage);
         //TODO: would be good to start the QGIV creation process here, but no guarantee we actually have
@@ -187,6 +192,11 @@ bool ViewProviderDrawingView::isShow() const
     return Visibility.getValue();
 }
 
+void ViewProviderDrawingView::dropObject(App::DocumentObject* docObj)
+{
+    getViewProviderPage()->dropObject(docObj);
+}
+
 void ViewProviderDrawingView::startRestoring()
 {
     Gui::ViewProviderDocumentObject::startRestoring();
@@ -417,6 +427,11 @@ void ViewProviderDrawingView::stackBottom()
     qView->setStack(minZ - 1);
 }
 
+const char*  ViewProviderDrawingView::whoAmI() const
+{
+    return m_myName.c_str();
+}
+
 TechDraw::DrawView* ViewProviderDrawingView::getViewObject() const
 {
     return dynamic_cast<TechDraw::DrawView*>(pcObject);

src/Mod/TechDraw/Gui/ViewProviderDrawingView.h

@@ -31,6 +31,7 @@
 #include <Gui/ViewProviderDocumentObject.h>
 #include <Mod/TechDraw/App/DrawView.h>
 
+#include "ViewProviderDrawingViewExtension.h"
 
 namespace TechDraw {
 class DrawView;
@@ -41,7 +42,8 @@ class QGIView;
 class MDIViewPage;
 class ViewProviderPage;
 
-class TechDrawGuiExport ViewProviderDrawingView : public Gui::ViewProviderDocumentObject
+class TechDrawGuiExport ViewProviderDrawingView : public Gui::ViewProviderDocumentObject,
+                                                  public ViewProviderDrawingViewExtension
 {
     PROPERTY_HEADER_WITH_OVERRIDE(TechDrawGui::ViewProviderDrawingView);
 
@@ -62,6 +64,8 @@ public:
     void show() override;
     bool isShow() const override;
 
+    void dropObject(App::DocumentObject* docObj) override;
+
     void onChanged(const App::Property *prop) override;
     void updateData(const App::Property*) override;
 
@@ -93,11 +97,13 @@ public:
     virtual void stackBottom();
     virtual int getZ() {return StackOrder.getValue();}
 
+    const char* whoAmI() const;
+
 private:
     void multiParentPaint(std::vector<TechDraw::DrawPage*>& pages);
     void singleParentPaint(const TechDraw::DrawView* dv);
 
-
+    std::string m_myName;
 };
 
 } // namespace TechDrawGui

src/Mod/TechDraw/Gui/ViewProviderDrawingViewExtension.cpp

@@ -0,0 +1,108 @@
+/***************************************************************************
+ *   Copyright (c) 2022 WandererFan <wandererfan@gmail.com>                *
+ *                                                                         *
+ *   This file is part of the FreeCAD CAx development system.              *
+ *                                                                         *
+ *   This library is free software; you can redistribute it and/or         *
+ *   modify it under the terms of the GNU Library General Public           *
+ *   License as published by the Free Software Foundation; either          *
+ *   version 2 of the License, or (at your option) any later version.      *
+ *                                                                         *
+ *   This library  is distributed in the hope that it will be useful,      *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU Library General Public License for more details.                  *
+ *                                                                         *
+ *   You should have received a copy of the GNU Library General Public     *
+ *   License along with this library; see the file COPYING.LIB. If not,    *
+ *   write to the Free Software Foundation, Inc., 59 Temple Place,         *
+ *   Suite 330, Boston, MA  02111-1307, USA                                *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "PreCompiled.h"
+
+#ifndef _PreComp_
+# include <QMessageBox>
+#endif
+
+#include <App/Document.h>
+#include <App/DocumentObject.h>
+#include <Base/Console.h>
+#include <Base/Tools.h>
+
+#include <Mod/TechDraw/App/DrawPage.h>
+#include <Mod/TechDraw/App/DrawTemplate.h>
+
+#include "ViewProviderDrawingViewExtension.h"
+#include "ViewProviderDrawingView.h"
+#include "ViewProviderPage.h"
+
+using namespace TechDrawGui;
+
+EXTENSION_PROPERTY_SOURCE(TechDrawGui::ViewProviderDrawingViewExtension, Gui::ViewProviderExtension)
+
+ViewProviderDrawingViewExtension::ViewProviderDrawingViewExtension()
+{
+    initExtensionType(ViewProviderDrawingViewExtension::getExtensionClassTypeId());
+}
+
+ViewProviderDrawingViewExtension::~ViewProviderDrawingViewExtension()
+{
+}
+
+bool ViewProviderDrawingViewExtension::extensionCanDragObjects() const {
+    return true;
+}
+
+//we don't support dragging children of Views (Dimensions, Balloons, Hatches, etc) now, but we don't want another
+//extension to drag our children and cause problems
+bool ViewProviderDrawingViewExtension::extensionCanDragObject(App::DocumentObject* docObj) const {
+    (void)docObj;
+    return true;
+}
+
+//the default drag will remove the object from the document until it is dropped and re-added, so we claim
+//to do the dragging.
+void ViewProviderDrawingViewExtension::extensionDragObject(App::DocumentObject* obj) {
+    (void)obj;
+}
+
+//we don't support dropping of new children of Views (Dimensions, Balloons, Hatches, etc) now, but we don't want another
+//extension to try to drop on us and cause problems
+bool ViewProviderDrawingViewExtension::extensionCanDropObjects() const {
+    return true;
+}
+
+//let the page have any drops we receive
+bool ViewProviderDrawingViewExtension::extensionCanDropObject(App::DocumentObject* obj) const {
+    return getViewProviderDrawingView()->getViewProviderPage()->getVPPExtension()->extensionCanDropObject(obj);
+}
+
+//let the page have any drops we receive
+void ViewProviderDrawingViewExtension::extensionDropObject(App::DocumentObject* obj) {
+    getViewProviderDrawingView()->getViewProviderPage()->getVPPExtension()->extensionDropObject(obj);
+}
+
+const ViewProviderDrawingView* ViewProviderDrawingViewExtension::getViewProviderDrawingView() const
+{
+    return dynamic_cast<const ViewProviderDrawingView*>(getExtendedViewProvider());
+}
+
+const char*  ViewProviderDrawingViewExtension::whoAmI() const
+{
+    auto parent = getViewProviderDrawingView();
+    if (parent) {
+        return parent->whoAmI();
+    }
+    return nullptr;
+}
+
+namespace Gui {
+EXTENSION_PROPERTY_SOURCE_TEMPLATE(ViewProviderDrawingViewExtensionPython, ViewProviderDrawingViewExtension)
+
+// explicit template instantiation
+template class GuiExport ViewProviderExtensionPythonT<ViewProviderDrawingViewExtension>;
+}
+
+

src/Mod/TechDraw/Gui/ViewProviderDrawingViewExtension.h

@@ -0,0 +1,63 @@
+/***************************************************************************
+ *   Copyright (c) 2022 WandererFan <wandererfan@gmail.com>                *
+ *                                                                         *
+ *   This file is part of the FreeCAD CAx development system.              *
+ *                                                                         *
+ *   This library is free software; you can redistribute it and/or         *
+ *   modify it under the terms of the GNU Library General Public           *
+ *   License as published by the Free Software Foundation; either          *
+ *   version 2 of the License, or (at your option) any later version.      *
+ *                                                                         *
+ *   This library  is distributed in the hope that it will be useful,      *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU Library General Public License for more details.                  *
+ *                                                                         *
+ *   You should have received a copy of the GNU Library General Public     *
+ *   License along with this library; see the file COPYING.LIB. If not,    *
+ *   write to the Free Software Foundation, Inc., 59 Temple Place,         *
+ *   Suite 330, Boston, MA  02111-1307, USA                                *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef TECHDRAWGUI_VIEWPROVIDERDRAWINGVIEWEXTENSION_H
+#define TECHDRAWGUI_VIEWPROVIDERDRAWINGVIEWEXTENSION_H
+
+#include <Mod/TechDraw/TechDrawGlobal.h>
+#include <Gui/ViewProviderExtension.h>
+#include <Gui/ViewProviderExtensionPy.h>
+#include <Gui/ViewProviderExtensionPython.h>
+
+namespace TechDrawGui
+{
+class ViewProviderDrawingView;
+
+class TechDrawGuiExport ViewProviderDrawingViewExtension : public Gui::ViewProviderExtension
+{
+    EXTENSION_PROPERTY_HEADER_WITH_OVERRIDE(Gui::ViewProviderDrawingViewExtension);
+
+public:
+    /// Constructor
+    ViewProviderDrawingViewExtension();
+    ~ViewProviderDrawingViewExtension() override;
+
+    bool extensionCanDragObjects() const override;
+    bool extensionCanDragObject(App::DocumentObject*) const override;
+    void extensionDragObject(App::DocumentObject*) override;
+    bool extensionCanDropObjects() const override;
+    bool extensionCanDropObject(App::DocumentObject*) const override;
+    void extensionDropObject(App::DocumentObject*) override;
+
+    const ViewProviderDrawingView* getViewProviderDrawingView() const;
+    const char* whoAmI() const;
+
+private:
+};
+
+using ViewProviderDrawingViewExtensionPython = Gui::ViewProviderExtensionPythonT<ViewProviderDrawingViewExtension>;
+
+} //namespace Gui
+
+#endif // TECHDRAWGUI_VIEWPROVIDERDRAWINGVIEWEXTENSION_H
+
+

src/Mod/TechDraw/Gui/ViewProviderPage.cpp

@@ -61,7 +61,7 @@
 #include "QGVPage.h"
 #include "ViewProviderTemplate.h"
 #include "ViewProviderPage.h"
-
+#include "ViewProviderPageExtension.h"
 
 using namespace TechDrawGui;
 using namespace TechDraw;
@@ -82,12 +82,14 @@ ViewProviderPage::ViewProviderPage()
     m_graphicsView(nullptr),
     m_graphicsScene(nullptr)
 {
+    initExtension(this);
+
     sPixmap = "TechDraw_TreePage";
     static const char *group = "Grid";
 
     ADD_PROPERTY_TYPE(ShowFrames ,(true), group, App::Prop_None, "Show or hide View frames and Labels on this Page");
     ADD_PROPERTY_TYPE(ShowGrid ,(PreferencesGui::showGrid()), group, App::Prop_None, "Show or hide a grid on this Page");
-    ADD_PROPERTY_TYPE(GridSpacing, (PreferencesGui::gridSpacing()), group, (App::PropertyType)(App::Prop_None),
+    ADD_PROPERTY_TYPE(GridSpacing, (PreferencesGui::gridSpacing()), group, (App::PropertyType::Prop_None),
                      "Grid line spacing in mm");
 
     ShowFrames.setStatus(App::Property::Hidden, true);
@@ -462,57 +464,29 @@ bool ViewProviderPage::canDelete(App::DocumentObject *obj) const
 
 bool ViewProviderPage::canDragObjects() const
 {
-//    Base::Console().Message("VPP:canDragObjects()\n");
-    return ViewProviderDocumentObject::canDragObjects();
+    return getVPPExtension()->extensionCanDragObjects();
 }
 
 bool ViewProviderPage::canDragObject(App::DocumentObject* docObj) const
 {
-//    Base::Console().Message("VPP:canDragObject()\n");
-    if (docObj->isDerivedFrom(TechDraw::DrawProjGroupItem::getClassTypeId())) {
-        //DPGI can not be dragged from the Page as it belongs to DPG, not Page
-        return false;
-    }
-
-    if (docObj->isDerivedFrom(TechDraw::DrawView::getClassTypeId()) ) {
-        return true;
-    }
-    return false;
+    return getVPPExtension()->extensionCanDragObject(docObj);
 }
 
+bool ViewProviderPage::canDropObjectEx(App::DocumentObject* obj, App::DocumentObject *owner,
+        const char *subname, const std::vector<std::string> &elements) const
+{
+    return getVPPExtension()->extensionCanDropObjectEx(obj, owner, subname, elements);
+
+}
 
 bool ViewProviderPage::canDropObject(App::DocumentObject* docObj) const
 {
-//    Base::Console().Message("VPP:canDropObject()\n");
-    if (docObj->isDerivedFrom(TechDraw::DrawProjGroupItem::getClassTypeId())) {
-        //DPGI can not be dropped onto the Page as it belongs to DPG, not Page
-        return false;
-    }
-
-    if (docObj->isDerivedFrom(TechDraw::DrawView::getClassTypeId()) ) {
-        return true;
-    }
-    return false;
+    return getVPPExtension()->extensionCanDropObject(docObj);
 }
 
 void ViewProviderPage::dropObject(App::DocumentObject* docObj)
 {
-//    Base::Console().Message("VPP:dropObject()\n");
-    if (docObj->isDerivedFrom(TechDraw::DrawProjGroupItem::getClassTypeId())) {
-        //DPGI can not be dropped onto the Page as it belongs to DPG, not Page
-        ViewProviderDocumentObject::dropObject(docObj);
-        return;
-    }
-    if (docObj->isDerivedFrom(TechDraw::DrawView::getClassTypeId()) ) {
-        auto dv = static_cast<TechDraw::DrawView*>(docObj);
-        if (dv->findParentPage()) {
-            dv->findParentPage()->removeView(dv);
-        }
-        getDrawPage()->addView(dv);
-        //don't run ancestor's method as addView does everything we need
-        return;
-    }
-    ViewProviderDocumentObject::dropObject(docObj);
+    getVPPExtension()->extensionDropObject(docObj);
 }
 
 //! Redo the whole visual page
@@ -565,3 +539,15 @@ void  ViewProviderPage::setGrid()
         widget->updateViewport();
     }
 }
+
+ViewProviderPageExtension* ViewProviderPage::getVPPExtension() const
+{
+    auto vpe = getExtensionByType<ViewProviderPageExtension>();
+    auto vppe = static_cast<ViewProviderPageExtension*>(vpe);
+    return vppe;
+}
+
+const char*  ViewProviderPage::whoAmI() const
+{
+    return m_pageName.c_str();
+}

src/Mod/TechDraw/Gui/ViewProviderPage.h

@@ -32,6 +32,7 @@
 
 #include <App/PropertyUnits.h>
 #include <Gui/ViewProviderDocumentObject.h>
+#include <ViewProviderPageExtension.h>
 
 namespace TechDraw{
     class DrawPage;
@@ -43,7 +44,8 @@ class MDIViewPage;
 class QGVPage;
 class QGSPage;
 
-class TechDrawGuiExport ViewProviderPage : public Gui::ViewProviderDocumentObject
+class TechDrawGuiExport ViewProviderPage : public Gui::ViewProviderDocumentObject,
+                                           public ViewProviderPageExtension
 {
     PROPERTY_HEADER_WITH_OVERRIDE(TechDrawGui::ViewProviderPage);
 
@@ -63,7 +65,12 @@ public:
     bool canDragObjects() const override;
     bool canDragObject(App::DocumentObject* docObj) const override;
     bool canDropObject(App::DocumentObject* docObj) const override;
+
     void dropObject(App::DocumentObject* docObj) override;
+    void constDropObject(App::DocumentObject* docObj) const;
+
+    bool canDropObjectEx(App::DocumentObject *obj, App::DocumentObject *owner,
+            const char *subname, const std::vector<std::string> &elements) const override;
 
     bool useNewSelectionModel() const override {return false;}
     /// returns a list of all possible modes
@@ -110,6 +117,10 @@ public:
     QGSPage* getQGSPage(void) {return m_graphicsScene;}
     QGVPage* getQGVPage(void) {return m_graphicsView;}
 
+    ViewProviderPageExtension* getVPPExtension() const;
+
+    const char* whoAmI() const;
+
 protected:
     bool setEdit(int ModNum) override;
     void createMDIViewPage();

src/Mod/TechDraw/Gui/ViewProviderPageExtension.cpp

@@ -0,0 +1,134 @@
+/***************************************************************************
+ *   Copyright (c) 2022 WandererFan <wandererfan@gmail.com>                *
+ *                                                                         *
+ *   This file is part of the FreeCAD CAx development system.              *
+ *                                                                         *
+ *   This library is free software; you can redistribute it and/or         *
+ *   modify it under the terms of the GNU Library General Public           *
+ *   License as published by the Free Software Foundation; either          *
+ *   version 2 of the License, or (at your option) any later version.      *
+ *                                                                         *
+ *   This library  is distributed in the hope that it will be useful,      *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU Library General Public License for more details.                  *
+ *                                                                         *
+ *   You should have received a copy of the GNU Library General Public     *
+ *   License along with this library; see the file COPYING.LIB. If not,    *
+ *   write to the Free Software Foundation, Inc., 59 Temple Place,         *
+ *   Suite 330, Boston, MA  02111-1307, USA                                *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "PreCompiled.h"
+
+#ifndef _PreComp_
+# include <QMessageBox>
+#endif
+
+#include <App/Document.h>
+#include <App/DocumentObject.h>
+#include <Base/Console.h>
+#include <Base/Tools.h>
+
+#include <Mod/TechDraw/App/DrawPage.h>
+#include <Mod/TechDraw/App/DrawTemplate.h>
+#include <Mod/TechDraw/App/DrawProjGroupItem.h>
+
+#include "ViewProviderPageExtension.h"
+#include "ViewProviderPage.h"
+
+using namespace TechDrawGui;
+
+EXTENSION_PROPERTY_SOURCE(TechDrawGui::ViewProviderPageExtension, Gui::ViewProviderExtension)
+
+ViewProviderPageExtension::ViewProviderPageExtension()
+{
+    initExtensionType(ViewProviderPageExtension::getExtensionClassTypeId());
+}
+
+ViewProviderPageExtension::~ViewProviderPageExtension()
+{
+}
+
+bool ViewProviderPageExtension::extensionCanDragObjects() const {
+    return true;
+}
+
+//we don't want another extension to drag our objects, so we say that we can handle this object
+bool ViewProviderPageExtension::extensionCanDragObject(App::DocumentObject* docObj) const {
+    (void) docObj;
+    return true;
+}
+
+//we don't take any action on drags.  everything is handling in drop
+void ViewProviderPageExtension::extensionDragObject(App::DocumentObject* obj) {
+    (void) obj;
+}
+
+//we handle our own drops
+bool ViewProviderPageExtension::extensionCanDropObjects() const {
+    return true;
+}
+
+bool ViewProviderPageExtension::extensionCanDropObject(App::DocumentObject* obj) const {
+    //only DrawView objects can live on pages (except special case Template)
+    if ( obj->isDerivedFrom(TechDraw::DrawView::getClassTypeId()) ) {
+        return true;
+    }
+    if ( obj->isDerivedFrom(TechDraw::DrawTemplate::getClassTypeId()) ) {
+        //don't let another extension try to drop templates
+        return true;
+    }
+
+    return false;
+}
+
+void ViewProviderPageExtension::extensionDropObject(App::DocumentObject* obj) {
+    if ( obj->isDerivedFrom(TechDraw::DrawView::getClassTypeId()) ) {
+        dropObject(obj);
+        return;
+    }
+}
+
+//this code used to live in ViewProviderPage
+void ViewProviderPageExtension::dropObject(App::DocumentObject* docObj)
+{
+    if (docObj->isDerivedFrom(TechDraw::DrawProjGroupItem::getClassTypeId())) {
+        //DPGI can not be dropped onto the Page as it belongs to DPG, not Page
+        return;
+    }
+    if (docObj->isDerivedFrom(TechDraw::DrawView::getClassTypeId()) ) {
+        auto dv = static_cast<TechDraw::DrawView*>(docObj);
+        if (dv->findParentPage()) {
+            dv->findParentPage()->removeView(dv);
+        }
+        getViewProviderPage()->getDrawPage()->addView(dv);
+        //don't run ancestor's method as addView does everything we need
+        return;
+    }
+    //don't try to drop random objects
+}
+
+const ViewProviderPage* ViewProviderPageExtension::getViewProviderPage() const
+{
+    return dynamic_cast<const ViewProviderPage*>(getExtendedViewProvider());
+}
+
+
+const char*  ViewProviderPageExtension::whoAmI() const
+{
+    auto parent = getViewProviderPage();
+    if (parent) {
+        return parent->whoAmI();
+    }
+    return nullptr;
+}
+
+namespace Gui {
+EXTENSION_PROPERTY_SOURCE_TEMPLATE(ViewProviderPageExtensionPython, ViewProviderPageExtension)
+
+// explicit template instantiation
+template class GuiExport ViewProviderExtensionPythonT<ViewProviderPageExtension>;
+}
+

src/Mod/TechDraw/Gui/ViewProviderPageExtension.h

@@ -0,0 +1,64 @@
+/***************************************************************************
+ *   Copyright (c) 2022 WandererFan <wandererfan@gmail.com>                *
+ *                                                                         *
+ *   This file is part of the FreeCAD CAx development system.              *
+ *                                                                         *
+ *   This library is free software; you can redistribute it and/or         *
+ *   modify it under the terms of the GNU Library General Public           *
+ *   License as published by the Free Software Foundation; either          *
+ *   version 2 of the License, or (at your option) any later version.      *
+ *                                                                         *
+ *   This library  is distributed in the hope that it will be useful,      *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU Library General Public License for more details.                  *
+ *                                                                         *
+ *   You should have received a copy of the GNU Library General Public     *
+ *   License along with this library; see the file COPYING.LIB. If not,    *
+ *   write to the Free Software Foundation, Inc., 59 Temple Place,         *
+ *   Suite 330, Boston, MA  02111-1307, USA                                *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef TECHDRAWGUI_VIEWPROVIDERPAGEEXTENSION_H
+#define TECHDRAWGUI_VIEWPROVIDERPAGEEXTENSION_H
+
+#include <Mod/TechDraw/TechDrawGlobal.h>
+#include <Gui/ViewProviderExtension.h>
+#include <Gui/ViewProviderExtensionPy.h>
+#include <Gui/ViewProviderExtensionPython.h>
+
+namespace TechDrawGui
+{
+class ViewProviderPage;
+
+class TechDrawGuiExport ViewProviderPageExtension : public Gui::ViewProviderExtension
+{
+    EXTENSION_PROPERTY_HEADER_WITH_OVERRIDE(Gui::ViewProviderPageExtension);
+
+public:
+    /// Constructor
+    ViewProviderPageExtension();
+    ~ViewProviderPageExtension() override;
+
+    bool extensionCanDragObjects() const override;
+    bool extensionCanDragObject(App::DocumentObject*) const override;
+    void extensionDragObject(App::DocumentObject*) override;
+    bool extensionCanDropObjects() const override;
+    bool extensionCanDropObject(App::DocumentObject*) const override;
+    void extensionDropObject(App::DocumentObject*) override;
+
+    void dropObject(App::DocumentObject* docObj);
+
+    const ViewProviderPage* getViewProviderPage() const;
+    const char* whoAmI() const;
+
+private:
+};
+
+using ViewProviderPageExtensionPython = Gui::ViewProviderExtensionPythonT<ViewProviderPageExtension>;
+
+} //namespace Gui
+
+#endif // TECHDRAWGUI_VIEWPROVIDERPAGEEXTENSION_H
+

src/Mod/TechDraw/Gui/ViewProviderTemplate.cpp

@@ -56,20 +56,30 @@ PROPERTY_SOURCE(TechDrawGui::ViewProviderTemplate, Gui::ViewProviderDocumentObje
 //**************************************************************************
 // Construction/Destruction
 
-ViewProviderTemplate::ViewProviderTemplate()
+ViewProviderTemplate::ViewProviderTemplate() :
+    m_myName(std::string())
 {
+    initExtension(this);
+
     sPixmap = "TechDraw_TreePageTemplate";
 
     DisplayMode.setStatus(App::Property::Hidden, true);
 }
 
-ViewProviderTemplate::~ViewProviderTemplate()
+void ViewProviderTemplate::attach(App::DocumentObject *pcFeat)
 {
+//    Base::Console().Message("VPT::attach(%s)\n", pcFeat->getNameInDocument());
+    ViewProviderDocumentObject::attach(pcFeat);
+
+    auto feature = getTemplate();
+    if (feature) {
+        m_myName = feature->getNameInDocument();
+    }
 }
 
 void ViewProviderTemplate::updateData(const App::Property* prop)
 {
-    //This doesn't belong here.  Should be in attach?
+    //This doesn't belong here.  Should be in a ViewProviderSvgTemplate?
     if (getTemplate()->isDerivedFrom(TechDraw::DrawSVGTemplate::getClassTypeId())) {
         auto t = static_cast<TechDraw::DrawSVGTemplate*>(getTemplate());
         if (prop == &(t->Template)) {
@@ -217,3 +227,8 @@ TechDraw::DrawTemplate* ViewProviderTemplate::getTemplate() const
 {
     return dynamic_cast<TechDraw::DrawTemplate*>(pcObject);
 }
+
+const char*  ViewProviderTemplate::whoAmI() const
+{
+    return m_myName.c_str();
+}

src/Mod/TechDraw/Gui/ViewProviderTemplate.h

@@ -22,9 +22,12 @@
 
 #ifndef DRAWINGGUI_VIEWPROVIDERTEMPLATE_H
 #define DRAWINGGUI_VIEWPROVIDERTEMPLATE_H
-
-#include <Mod/TechDraw/TechDrawGlobal.h>
 
+#include <Mod/TechDraw/TechDrawGlobal.h>
+
+#include <Gui/ViewProviderDocumentObject.h>
+
+#include "ViewProviderTemplateExtension.h"
 namespace TechDraw{
     class DrawTemplate;
 }
@@ -33,7 +36,8 @@ namespace TechDrawGui {
 class QGITemplate;
 class MDIViewPage;
 
-class TechDrawGuiExport ViewProviderTemplate : public Gui::ViewProviderDocumentObject
+class TechDrawGuiExport ViewProviderTemplate : public Gui::ViewProviderDocumentObject,
+                                               public ViewProviderTemplateExtension
 {
     PROPERTY_HEADER_WITH_OVERRIDE(TechDrawGui::ViewProviderTemplate);
 
@@ -41,7 +45,9 @@ public:
     /// constructor
     ViewProviderTemplate();
     /// destructor
-    virtual ~ViewProviderTemplate();
+    ~ViewProviderTemplate() override = default;
+
+    void attach(App::DocumentObject *) override;
 
     virtual bool useNewSelectionModel(void) const override {return false;}
     virtual void updateData(const App::Property*) override;
@@ -56,6 +62,11 @@ public:
 
     void setMarkers(bool state);
     virtual bool onDelete(const std::vector<std::string> &) override;
+
+    const char* whoAmI() const;
+
+private:
+    std::string m_myName;
 };
 
 } // namespace TechDrawGui

src/Mod/TechDraw/Gui/ViewProviderTemplateExtension.cpp

@@ -0,0 +1,101 @@
+/***************************************************************************
+ *   Copyright (c) 2022 WandererFan <wandererfan@gmail.com>                *
+ *                                                                         *
+ *   This file is part of the FreeCAD CAx development system.              *
+ *                                                                         *
+ *   This library is free software; you can redistribute it and/or         *
+ *   modify it under the terms of the GNU Library General Public           *
+ *   License as published by the Free Software Foundation; either          *
+ *   version 2 of the License, or (at your option) any later version.      *
+ *                                                                         *
+ *   This library  is distributed in the hope that it will be useful,      *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU Library General Public License for more details.                  *
+ *                                                                         *
+ *   You should have received a copy of the GNU Library General Public     *
+ *   License along with this library; see the file COPYING.LIB. If not,    *
+ *   write to the Free Software Foundation, Inc., 59 Temple Place,         *
+ *   Suite 330, Boston, MA  02111-1307, USA                                *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "PreCompiled.h"
+
+#ifndef _PreComp_
+# include <QMessageBox>
+#endif
+
+#include <App/Document.h>
+#include <App/DocumentObject.h>
+#include <Base/Console.h>
+#include <Base/Tools.h>
+
+#include <Mod/TechDraw/App/DrawPage.h>
+#include <Mod/TechDraw/App/DrawTemplate.h>
+
+#include "ViewProviderTemplateExtension.h"
+#include "ViewProviderTemplate.h"
+#include "ViewProviderPage.h"
+
+using namespace TechDrawGui;
+
+EXTENSION_PROPERTY_SOURCE(TechDrawGui::ViewProviderTemplateExtension, Gui::ViewProviderExtension)
+
+ViewProviderTemplateExtension::ViewProviderTemplateExtension()
+{
+    initExtensionType(ViewProviderTemplateExtension::getExtensionClassTypeId());
+}
+
+ViewProviderTemplateExtension::~ViewProviderTemplateExtension()
+{
+}
+
+//there are no child objects to drag currently, so we will say we handle any dragging rather than letting some
+//other extension trying to drag and causing problems.
+bool ViewProviderTemplateExtension::extensionCanDragObjects() const {
+    return true;
+}
+
+//there are no child objects to drag currently, so we will say we handle any dragging
+bool ViewProviderTemplateExtension::extensionCanDragObject(App::DocumentObject* docObj) const {
+    (void) docObj;
+    return true;
+}
+
+//templates do not accept drops, so rather that let some other extension try to drop into a template, we will
+//claim that we can handle drops
+bool ViewProviderTemplateExtension::extensionCanDropObjects() const {
+    return true;
+}
+
+//templates do not accept drops, so rather that let some other extension try to drop into a template, we will
+//claim that we can handle drops
+bool ViewProviderTemplateExtension::extensionCanDropObject(App::DocumentObject* docObj) const {
+    (void)docObj;
+    return true;
+}
+
+const ViewProviderTemplate* ViewProviderTemplateExtension::getViewProviderTemplate() const
+{
+    return dynamic_cast<const ViewProviderTemplate*>(getExtendedViewProvider());
+}
+
+const char*  ViewProviderTemplateExtension::whoAmI() const
+{
+    auto parent = getViewProviderTemplate();
+    if (parent) {
+        return parent->whoAmI();
+    }
+    return nullptr;
+}
+
+namespace Gui {
+EXTENSION_PROPERTY_SOURCE_TEMPLATE(ViewProviderTemplateExtensionPython, ViewProviderTemplateExtension)
+
+// explicit template instantiation
+template class GuiExport ViewProviderExtensionPythonT<ViewProviderTemplateExtension>;
+}
+
+
+

src/Mod/TechDraw/Gui/ViewProviderTemplateExtension.h

@@ -0,0 +1,62 @@
+/***************************************************************************
+ *   Copyright (c) 2022 WandererFan <wandererfan@gmail.com>                *
+ *                                                                         *
+ *   This file is part of the FreeCAD CAx development system.              *
+ *                                                                         *
+ *   This library is free software; you can redistribute it and/or         *
+ *   modify it under the terms of the GNU Library General Public           *
+ *   License as published by the Free Software Foundation; either          *
+ *   version 2 of the License, or (at your option) any later version.      *
+ *                                                                         *
+ *   This library  is distributed in the hope that it will be useful,      *
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+ *   GNU Library General Public License for more details.                  *
+ *                                                                         *
+ *   You should have received a copy of the GNU Library General Public     *
+ *   License along with this library; see the file COPYING.LIB. If not,    *
+ *   write to the Free Software Foundation, Inc., 59 Temple Place,         *
+ *   Suite 330, Boston, MA  02111-1307, USA                                *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef TECHDRAWGUI_VIEWPROVIDERTEMPLATEEXTENSION_H
+#define TECHDRAWGUI_VIEWPROVIDERTEMPLATEEXTENSION_H
+
+#include <Mod/TechDraw/TechDrawGlobal.h>
+#include <Gui/ViewProviderExtension.h>
+#include <Gui/ViewProviderExtensionPy.h>
+#include <Gui/ViewProviderExtensionPython.h>
+
+namespace TechDrawGui
+{
+class ViewProviderTemplate;
+
+class TechDrawGuiExport ViewProviderTemplateExtension : public Gui::ViewProviderExtension
+{
+    EXTENSION_PROPERTY_HEADER_WITH_OVERRIDE(Gui::ViewProviderTemplateExtension);
+
+public:
+    /// Constructor
+    ViewProviderTemplateExtension();
+    ~ViewProviderTemplateExtension() override;
+
+    bool extensionCanDragObjects() const override;
+    bool extensionCanDragObject(App::DocumentObject* docObj) const override;
+    bool extensionCanDropObjects() const override;
+    bool extensionCanDropObject(App::DocumentObject* docObj) const override;
+
+    const ViewProviderTemplate* getViewProviderTemplate() const;
+    const char* whoAmI() const;
+
+private:
+};
+
+using ViewProviderTemplateExtensionPython = Gui::ViewProviderExtensionPythonT<ViewProviderTemplateExtension>;
+
+} //namespace Gui
+
+#endif // TECHDRAWGUI_VIEWPROVIDERTEMPLATEEXTENSION_H
+
+
+