FEM: Correctly implement Drag/Drop for post objects

src/Mod/Fem/App/FemPostGroupExtension.cpp

@@ -143,6 +143,13 @@ void FemPostGroupExtension::onExtendedUnsetupObject()
     }
 }
 
+bool FemPostGroupExtension::allowObject(App::DocumentObject* obj)
+{
+    // only filters may be added
+    return obj->isDerivedFrom(Fem::FemPostFilter::getClassTypeId());
+}
+
+
 void FemPostGroupExtension::recomputeChildren()
 {
     for (const auto& obj : Group.getValues()) {

src/Mod/Fem/App/FemPostGroupExtension.h

@@ -59,6 +59,7 @@ public:
 protected:
     void extensionOnChanged(const App::Property* p) override;
     void onExtendedUnsetupObject() override;
+    bool allowObject(App::DocumentObject* obj) override;
 
 private:
     bool m_blockChange = false;

src/Mod/Fem/App/FemPostPipeline.cpp

@@ -245,6 +245,18 @@ Fem::FemPostFunctionProvider* FemPostPipeline::getFunctionProvider() {
     return nullptr;
 }
 
+bool FemPostPipeline::allowObject(App::DocumentObject* obj)
+{
+    // we additionally allow FunctionPRoviders to be added
+    if (obj->isDerivedFrom(FemPostFunctionProvider::getClassTypeId())) {
+        return true;
+    }
+
+    // and all standart Post objects the group can handle
+    return FemPostGroupExtension::allowObject(obj);
+}
+
+
 bool FemPostPipeline::canRead(Base::FileInfo File)
 {
 

src/Mod/Fem/App/FemPostPipeline.h

@@ -108,6 +108,7 @@ public:
 
 protected:
     void onChanged(const App::Property* prop) override;
+    bool allowObject(App::DocumentObject* obj) override;
 
 private:
     App::Enumeration  m_frameEnum;

src/Mod/Fem/Gui/ViewProviderFemPostBranchFilter.cpp

@@ -24,6 +24,7 @@
 
 #include "TaskPostBoxes.h"
 #include "ViewProviderFemPostBranchFilter.h"
+#include <Mod/Fem/App/FemPostGroupExtension.h>
 
 
 using namespace FemGui;
@@ -51,3 +52,17 @@ void ViewProviderFemPostBranchFilter::setupTaskDialog(TaskDlgPost* dlg)
     FemGui::ViewProviderFemPostObject::setupTaskDialog(dlg);
 }
 
+bool ViewProviderFemPostBranchFilter::acceptReorderingObjects() const {
+    return true;
+}
+
+bool ViewProviderFemPostBranchFilter::canDragObjectToTarget(App::DocumentObject* obj, App::DocumentObject* target) const {
+
+    // allow drag only to other post groups
+    if (target) {
+        return target->hasExtension(Fem::FemPostGroupExtension::getExtensionClassTypeId());
+    }
+    else {
+        return false;
+    }
+}

src/Mod/Fem/Gui/ViewProviderFemPostBranchFilter.h

@@ -49,6 +49,10 @@ public:
 protected:
     virtual void setupTaskDialog(TaskDlgPost* dlg) override;
 
+    // change default group drag/drop behaviour sligthly
+    bool acceptReorderingObjects() const override;
+    bool canDragObjectToTarget(App::DocumentObject* obj, App::DocumentObject* target) const override;
+
     // override, to not show/hide children as the parent is shown/hidden like normal groups
     void extensionHide() override {};
     void extensionShow() override {};

src/Mod/Fem/Gui/ViewProviderFemPostPipeline.cpp

@@ -229,6 +229,22 @@ void ViewProviderFemPostPipeline::setupTaskDialog(TaskDlgPost* dlg)
 }
 
 
+bool ViewProviderFemPostPipeline::acceptReorderingObjects() const {
+    return true;
+}
+
+bool ViewProviderFemPostPipeline::canDragObjectToTarget(App::DocumentObject* obj, App::DocumentObject* target) const {
+
+    // allow drag only to other post groups
+    if (target) {
+        return target->hasExtension(Fem::FemPostGroupExtension::getExtensionClassTypeId());
+    }
+    else {
+        return false;
+    }
+}
+
+
 PyObject* ViewProviderFemPostPipeline::getPyObject()
 {
     if (!pyViewObject) {

src/Mod/Fem/Gui/ViewProviderFemPostPipeline.h

@@ -55,6 +55,10 @@ protected:
     void updateFunctionSize();
     virtual void setupTaskDialog(TaskDlgPost* dlg) override;
 
+    // change default group drag/drop behaviour sligthly
+    bool acceptReorderingObjects() const override;
+    bool canDragObjectToTarget(App::DocumentObject* obj, App::DocumentObject* target) const override;
+
     // override, to not show/hide children as the parent is shown/hidden like normal groups
     void extensionHide() override {};
     void extensionShow() override {};