added clear action for browsing history

gui/base.qrc

@@ -9,5 +9,6 @@
         <file>resources/resultset_previous.png</file>
         <file>resources/resultset_next.png</file>
         <file>resources/resultset_last.png</file>
+        <file>resources/cross.png</file>
     </qresource>
 </RCC>

gui/designwidget.cc

@@ -125,11 +125,27 @@ DesignWidget::DesignWidget(QWidget *parent) : QWidget(parent), ctx(nullptr), net
         updateButtons();
     });
 
+    actionClear = new QAction("", this);
+    actionClear->setIcon(QIcon(":/icons/resources/cross.png"));
+    actionClear->setEnabled(true);
+    connect(actionClear, &QAction::triggered, this, [this] {
+        history_index = -1;
+        history.clear();
+        QTreeWidgetItem *clickItem = treeWidget->selectedItems().at(0);
+        if (clickItem->parent()) {
+            ElementType type = static_cast<ElementTreeItem *>(clickItem)->getType();
+            if (type != ElementType::NONE)
+                addToHistory(treeWidget->selectedItems().at(0));
+        }
+        updateButtons();
+    });
+
     QToolBar *toolbar = new QToolBar();
     toolbar->addAction(actionFirst);
     toolbar->addAction(actionPrev);
     toolbar->addAction(actionNext);
     toolbar->addAction(actionLast);
+    toolbar->addAction(actionClear);
 
     QWidget *topWidget = new QWidget();
     QVBoxLayout *vbox1 = new QVBoxLayout();

gui/designwidget.h

@@ -102,6 +102,7 @@ class DesignWidget : public QWidget
     QAction *actionPrev;
     QAction *actionNext;
     QAction *actionLast;
+    QAction *actionClear;
 
     QColor highlightColors[8];
     QMap<QTreeWidgetItem *, int> highlightSelected;