Qt工程文件里创建新子项目的按钮是灰的，按不了，怎么办？

Qt 5.6样例： MainWindow.h： #ifndef MAINWINDOW_H#define MAINWINDOW_H#include #include class MainWindow : public QMainWindow{ Q_OBJECTpublic: MainWindow(QWidget *parent = 0); ~MainWindow();private: void initialAction(); void initialMenuBar(); void initialToolBar(); void initialStatusBar(); void open(); QAction *openAction;};#endif // MAINWINDOW_H MainWindow.cpp： #include #include #include #include #include #include "MainWindow.h"MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent){ setWindowTitle(tr("Main Window")); initialAction(); initialMenuBar(); initialToolBar(); initialStatusBar();}MainWindow::~MainWindow(){}void MainWindow::initialAction(){ openAction = new QAction(QIcon(":/images/doc-open"), QObject::tr("&Open..."), this); openAction->setShortcuts(QKeySequence::Open); connect(openAction, &QAction::triggered, this, &MainWindow::open);}void MainWindow::initialMenuBar(){ QMenu *file = menuBar()->addMenu(QObject::tr("&File")); file->addAction(openAction);}void MainWindow::initialToolBar(){ QToolBar *toolBar = addToolBar(QObject::tr("&File")); toolBar->addAction(openAction);}void MainWindow::initialStatusBar(){ statusBar(); openAction->setStatusTip(QObject::tr("Open an existing file"));}void MainWindow::open(){ QMessageBox::information(this, tr("Information"), tr("Open"));}