reduce SessionModel usage for SampleModel

GUI/Model/From/GUIDomainSampleVisitor.cpp

@@ -132,7 +132,7 @@ void GUIDomainSampleVisitor::visit(const Layer* node)
 
 void GUIDomainSampleVisitor::visit(const MultiLayer* node)
 {
-    auto* multilayer_item = m_sampleModel->insertItem<MultiLayerItem>();
+    auto* multilayer_item = m_sampleModel->addMultiLayer();
     multilayer_item->setItemName(node->sampleName().c_str());
     multilayer_item->crossCorrLength().set(node->crossCorrLength());
     multilayer_item->setExternalField(node->externalField());

GUI/Model/From/SampleListModel.cpp

@@ -13,6 +13,7 @@
 //  ************************************************************************************************
 
 #include "GUI/Model/From/SampleListModel.h"
+#include "Base/Util/Assert.h"
 #include "GUI/Model/From/GUIExamplesFactory.h"
 #include "GUI/Model/Sample/MultiLayerItem.h"
 #include "GUI/Model/Sample/SampleModel.h"
@@ -32,7 +33,8 @@ SampleListModel::SampleListModel(QObject* parent, SampleModel* model)
 
 MultiLayerItem* SampleListModel::topMostItem() const
 {
-    return m_sampleModel->topItem<MultiLayerItem>();
+    ASSERT(!m_sampleModel->multiLayerItems().isEmpty());
+    return m_sampleModel->multiLayerItems().first();
 }
 
 int SampleListModel::rowCount(const QModelIndex& parent) const
@@ -131,7 +133,7 @@ QModelIndex SampleListModel::createSample()
 
     const int row = m_sampleModel->multiLayerItems().size();
     beginInsertRows(QModelIndex(), row, row);
-    auto* multilayer_item = m_sampleModel->insertItem<MultiLayerItem>();
+    auto* multilayer_item = m_sampleModel->addMultiLayer();
     multilayer_item->setItemName(suggestName(topItemNames(m_sampleModel), "Sample"));
     endInsertRows();
     return indexForItem(multilayer_item);

GUI/Model/Sample/SampleModel.cpp

@@ -77,6 +77,11 @@ QVector<ItemWithMaterial*> SampleModel::itemsWithMaterial() const
     return result;
 }
 
+MultiLayerItem* SampleModel::addMultiLayer()
+{
+    return insertItem<MultiLayerItem>();
+}
+
 void SampleModel::removeMultiLayer(MultiLayerItem* item)
 {
     removeItem(item);

GUI/Model/Sample/SampleModel.h

@@ -38,6 +38,8 @@ public:
     //! Returns vector of SessionItems having MaterialProperty on board.
     QVector<ItemWithMaterial*> itemsWithMaterial() const;
 
+    //! Adds a multilayer and returns the new item.
+    MultiLayerItem* addMultiLayer();
     void removeMultiLayer(MultiLayerItem* item);
 
 signals:

GUI/View/SampleDesigner/ScriptPanel.cpp

@@ -111,7 +111,7 @@ QString ScriptPanel::generateCodeSnippet()
     m_cautionSign->clear();
     QString result;
 
-    for (const MultiLayerItem* sampleItem : m_sampleModel->topItems<MultiLayerItem>()) {
+    for (const MultiLayerItem* sampleItem : m_sampleModel->multiLayerItems()) {
         try {
             auto multilayer = GUI::Model::DomainObjectBuilder::buildMultiLayer(*sampleItem);
             if (!result.isEmpty())

GUI/View/Toplevel/SimulationView.cpp

@@ -236,7 +236,7 @@ void SimulationView::updateFunctionalityNarrowing()
 
 QVector<MultiLayerItem*> SimulationView::multiLayerItems() const
 {
-    return m_document->sampleModel()->topItems<MultiLayerItem>();
+    return m_document->sampleModel()->multiLayerItems();
 }
 
 QVector<InstrumentItem*> SimulationView::instrumentItems() const

Tests/Unit/GUI/TestMultiLayerItem.cpp

@@ -16,7 +16,7 @@ TEST_F(TestMultiLayerItem, twoLayerSystem)
 {
     SampleModel model;
 
-    auto* multilayer = model.insertItem<MultiLayerItem>();
+    auto* multilayer = model.addMultiLayer();
     auto* top = model.insertItem<LayerItem>(multilayer);
     auto* bottom = model.insertItem<LayerItem>(multilayer);
 
@@ -45,7 +45,7 @@ TEST_F(TestMultiLayerItem, threeLayerSystem)
 {
     SampleModel model;
 
-    auto* multilayer = model.insertItem<MultiLayerItem>();
+    auto* multilayer = model.addMultiLayer();
     auto* top = model.insertItem<LayerItem>(multilayer);
     auto* middle = model.insertItem<LayerItem>(multilayer);
     auto* bottom = model.insertItem<LayerItem>(multilayer);
@@ -80,7 +80,7 @@ TEST_F(TestMultiLayerItem, movingMiddleLayerOnTop)
 {
     SampleModel model;
 
-    auto* multilayer = model.insertItem<MultiLayerItem>();
+    auto* multilayer = model.addMultiLayer();
     auto* top = model.insertItem<LayerItem>(multilayer);
     auto* middle = model.insertItem<LayerItem>(multilayer);
     auto* bottom = model.insertItem<LayerItem>(multilayer);
@@ -128,7 +128,7 @@ TEST_F(TestMultiLayerItem, movingLayerOnCanvas)
 {
     SampleModel model;
 
-    auto* multilayer = model.insertItem<MultiLayerItem>();
+    auto* multilayer = model.addMultiLayer();
     auto* top = model.insertItem<LayerItem>(multilayer);
     model.insertItem<LayerItem>(multilayer);