InstrumentView cleanly separate updateActions/Editor

GUI/View/Views/InstrumentView.cpp

@@ -65,8 +65,11 @@ InstrumentView::InstrumentView()
 
     //... Finalize
 
-    connect(gDoc->instruments(), &InstrumentsSet::setChanged, this,
-            &InstrumentView::createWidgetsForCurrentInstrument);
+    connect(gDoc->instruments(), &InstrumentsSet::setChanged, [this]
+	{
+	    updateEditor();
+	    updateActions();
+	});
 
     updateActions();
 }
@@ -131,18 +134,26 @@ void InstrumentView::updateActions()
     m_save_action->setEnabled(enabled);
 }
 
-void InstrumentView::createWidgetsForCurrentInstrument()
+void InstrumentView::updateEditor()
 {
-    updateActions();
-
     InstrumentItem* t = m_set->currentItem();
-    if (!t) {
-        m_scroll_area->setWidget(new QWidget(m_scroll_area)); // blank widget
-        return;
-    }
+    if (t == m_displayed_item)
+	return;
+    m_displayed_item = t;
+    if (!t)
+	delete m_scroll_area->takeWidget();
+    else
+        m_scroll_area->setWidget(createEditor(t));
+}
 
-    auto* w = new QWidget(m_scroll_area);
-    auto* layout = new QVBoxLayout(w);
+QWidget* InstrumentView::createEditor(InstrumentItem* t)
+{
+    auto* result = new QWidget(m_scroll_area);
+
+    if (!t)
+	return result; // blank widget
+
+    auto* layout = new QVBoxLayout(result);
 
     //... Groupbox with instrument name and description (same layout for all instrument types)
 
@@ -189,5 +200,6 @@ void InstrumentView::createWidgetsForCurrentInstrument()
         ASSERT_NEVER;
 
     layout->addWidget(editor);
-    m_scroll_area->setWidget(w);
+
+    return result;
 }

GUI/View/Views/InstrumentView.h

@@ -32,11 +32,13 @@ public:
 private:
     void setToolbarActions(QToolBar* toolbar);
     void updateActions();
-    void createWidgetsForCurrentInstrument();
+    void updateEditor();
+    QWidget* createEditor(InstrumentItem*);
 
     InstrumentsSet* m_set;
     SetView* m_qlistview;
     QScrollArea* m_scroll_area;
+    InstrumentItem* m_displayed_item = nullptr;
 
     QAction* m_rm_action;
     QAction* m_cp_action;