[TD]fix fail on missing base view (#7856)

src/Mod/TechDraw/App/DrawProjGroup.cpp

@@ -423,6 +423,39 @@ bool DrawProjGroup::hasProjection(const char *viewProjType) const
     return false;
 }
 
+bool DrawProjGroup::canDelete(const char *viewProjType) const
+{
+//    Base::Console().Message("DPG::canDelete(%s)\n", viewProjType);
+    TechDraw::DrawProjGroupItem* foundItem(nullptr);
+    for( const auto it : Views.getValues() ) {
+        auto view( dynamic_cast<TechDraw::DrawProjGroupItem *>(it) );
+        if (!view) {
+            //should never have a item in DPG that is not a DPGI.
+            Base::Console().Log("PROBLEM - DPG::hasProjection finds non-DPGI in Group %s / %s\n",
+                                    getNameInDocument(), viewProjType);
+            throw Base::TypeError("Error: projection in DPG list is not a DPGI!");
+        }
+
+        if (strcmp(viewProjType, view->Type.getValueAsString()) == 0 ) {
+            foundItem = view;
+            break;
+        }
+    }
+
+    if (foundItem) {
+        auto linkedItems = foundItem->getInList();
+        for (auto& item : linkedItems) {
+            if (item == this) {
+                continue;
+            }
+            if (item->isDerivedFrom(TechDraw::DrawView::getClassTypeId())) {
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
 App::DocumentObject * DrawProjGroup::addProjection(const char *viewProjType)
 {
     DrawProjGroupItem *view( nullptr );

src/Mod/TechDraw/App/DrawProjGroup.h

@@ -78,7 +78,8 @@ public:
 
     /// Check if container has a view of a specific type
     bool hasProjection(const char *viewProjType) const;
-
+    ///check if it is safe to delete item
+    bool canDelete(const char *viewProjType) const;
     App::DocumentObject * getProjObj(const char *viewProjType) const;
     DrawProjGroupItem* getProjItem(const char *viewProjType) const;
 

src/Mod/TechDraw/Gui/TaskProjGroup.cpp

@@ -190,8 +190,10 @@ void TaskProjGroup::viewToggled(bool toggle)
                                 multiView->getNameInDocument(), viewNameCStr);
         changed = true;
     } else if ( !toggle && multiView->hasProjection( viewNameCStr ) ) {
-        multiView->removeProjection( viewNameCStr );
-        changed = true;
+        if (multiView->canDelete(viewNameCStr)) {
+            multiView->removeProjection( viewNameCStr );
+            changed = true;
+        }
     }
     if (changed) {
         if (multiView->ScaleType.isValue("Automatic")) {
@@ -473,6 +475,9 @@ void TaskProjGroup::setupViewCheckboxes(bool addConnections)
         const char *viewStr = viewChkIndexToCStr(i);
         if (viewStr && multiView->hasProjection(viewStr)) {
             box->setCheckState(Qt::Checked);
+            if (!multiView->canDelete(viewStr)) {
+                box->setEnabled(false);
+            }
         } else {
             box->setCheckState(Qt::Unchecked);
         }

src/Mod/TechDraw/Gui/ViewProviderViewPart.cpp

@@ -227,6 +227,10 @@ bool ViewProviderViewPart::setEdit(int ModNum)
     TechDraw::DrawViewPart* dvp = getViewObject();
     TechDraw::DrawViewDetail* dvd = dynamic_cast<TechDraw::DrawViewDetail*>(dvp);
     if (dvd) {
+        if (!dvd->BaseView.getValue()) {
+            Base::Console().Error("DrawViewDetail - %s - has no BaseView!\n", dvd->getNameInDocument());
+            return false;
+        }
         // clear the selection (convenience)
         Gui::Selection().clearSelection();
         Gui::Control().showDialog(new TaskDlgDetail(dvd));