update: release page when changed

mainwindow.cpp

@@ -120,6 +120,7 @@ void MainWindow::switchPage(QWidget *button) {
             existingPage->hide();
             ui->stackedWidget->removeWidget(existingPage);
             createdPageByButton.remove(button);
+            delete existingPage;  // 删除旧页面
         }
 
         QWidget *newPage = factory->createPage(this);