必须在QWidget之前构建一个QApplication?-MustconstructaQApplicationbeforeaQWidget

1  

Don't use extern or otherwise static variables which lead to creation of the widget before the QApplication is created in main. The QApplication must exist before the constructor of the QWidget is executed.

在创建QApplication之前，不要使用外部或其他静态变量来创建小部件。q应用程序必须在QWidget的构造函数执行之前存在。

Instead of sharing the variable via extern, either make the other windows members of the main window, and then make the windows known to each other by passing around pointers, or keep them private in MainWindow and request the actions from the subwindows e.g. via signal/slots. As a generic rule, don't use global variables but class members.

不是通过外部共享变量，而是让主窗口的其他窗口成员，然后通过传递指针来让窗口相互了解，或者让它们在主窗口中保持私有，并从子窗口请求操作，例如通过信号/插槽。作为一个通用规则，不要使用全局变量，而是使用类成员。

In the following FirstWindow (which is supposed hide main window and secondWindow) gets the main window and the second window passed via pointers and then just calls show/hide on them directly.

在下面的FirstWindow(应该隐藏主窗口和secondWindow)中，获取主窗口，第二个窗口通过指针传递，然后直接调用show/hide。

int main(int argc, char **argv) {
    QApplication app(argc, argv);

    MainWindow mainWindow;
    mainWindow.show();

    return app.exec();
}

In main window, have two members for the two other windows, say FirstWindow and SecondWindow: class MainWindow : public QMainWindow { ... private: FirstWindow *m_firstWindow; SecondWindow *m_secondWindow; };

在主窗口中，有两个其他窗口的成员，比如FirstWindow和SecondWindow: class MainWindow: public QMainWindow{…私人:FirstWindow * m_firstWindow;SecondWindow * m_secondWindow;};

MainWindow::MainWindow(QWidget *parent) {
     m_firstWindow = new FirstWindow; //not pass this as parent as you want to hide the main window while the others are visible)
     m_secOndWindow= new SecondWindow;
     m_firstWindow->setMainWindow(this);
     m_firstWindow->setSecond(m_secondWindow);
     m_firstWindow->show(); //Show first window immediately, leave second window hidden
}

MainWindow::~MainWindow() {
     //Manual deletion is necessary as no parent is passed. Alternatively, use QScopedPointer
     delete m_firstWindow;
     delete m_secondWindow;
}

FirstWindow, inline for brevity:

FirstWindow,内联简洁:

class FirstWindow : public QWidget {
    Q_OBJECT
public:
    explicit FirstWindow(QWidget *parent = 0) : QWidget(parent) {}

    void setMainWindow(MainWindow *mainWindow) { m_mainWindow = mainWindow); }
    void setSecondWindow(SecondWindow *secondWindow) { m_secOndWindow= secondWindow; }

private Q_SLOTS:
     void somethingHappened() { //e.g. some button was clicked
         m_mainWindow->hide();
         m_secondWindow->show();
     }
private: 
     MainWindow* m_mainWindow;
     SecondWindow* m_secondWindow;  
};

0  

Maybe not helping the former author, but others facing the problem. I simply got this error by mistaking a debug-library with a release one. So check your linker settings, if you are sure the implementation is done right (first instancing application and then using widgets).

也许不是帮助前作者，而是其他人面对问题。我只是错误地将一个调试库与一个发布版本错误地混淆了。因此，检查链接器设置，如果您确定实现是正确的(第一个实例应用程序，然后使用小部件)。