init graph as null

@@ -266,6 +266,8 @@ void GraphItem::path_highlighting(std::string start, std::string end)
 			n->setColor(QColor(255, 0, 0));
 		}
 	}
+
+	
 }
 
 //event handler

@@ -40,4 +40,5 @@ void MainWindow::test_func()
 	/*QMessageBox::information(this, "test", 
 		"test: "+QString::number(11));*/
 	graphWidget->path_highlight();
+	//graphWidget->update();
 }
\ No newline at end of file

@@ -45,6 +45,7 @@ void PaperGraphWidget::print_graph(ifstream& fin)
 void PaperGraphWidget::path_highlight()
 {
 	graphItem->path_highlighting(std::string(""), std::string(""));
+	scene->update();
 }
 
 void PaperGraphWidget::handleSelectionChanged(int idx)

@@ -27,7 +27,7 @@ private:
 
 	//Ui::PaperGraphWidgetClass ui;
 	QGraphicsScene *scene;
-	GraphItem *graphItem;
+	GraphItem *graphItem = nullptr;
 };
 
 #endif // PAPERGRAPHWIDGET_H