Q_OBJECT or not Q_OBJECT

喜夏-厌秋 提交于 2019-11-28 08:58:38

问题


I wrote a little program with a my own class within the main.cpp. Here the code:

#include <QApplication>
#include <QPushButton>
#include <QLabel>

class MyWidget : public QWidget {
    //Q_OBJECT
public:
    MyWidget(QWidget* parent = 0);
    QLabel* label;
    QString string;

signals:
public slots:
    void setTextLabel();

};

void MyWidget::setTextLabel() {
    label->setText("Test");
}


MyWidget::MyWidget(QWidget* parent) 
     : QWidget(parent) {

}

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

    MyWidget widget;
    widget.show();

    return app.exec();
}

it seems work but not "completely". My slot doens't work. I suppose i have to put Q_OBJECT. BUT, doing so, I got a list of errors, like this:

undefined reference to `vtable for MyWidget'
........................................
collect2: error: ld returned 1 exit status
make: *** [mywidget] Error 1

I can I manage that? Where the problem?


回答1:


Signals and slots in Qt are managed through the moc: meta object compiler. Basically, the moc generates additional C++ code for each class containing the Q_OBJECT macro in order to implement effectively the signals and slots mechanisms. The additional code is then linked to the original class declaration.

The problem here is that your class is declared in main.cpp: this conflicts with how the moc is working with your code. You should declare your class in a separate header.

More about the moc

Edit: as hyde pointed, an alternative is to include in your cpp the file generated by the moc; more details




回答2:


just append the line #include"main.moc" to your cpp source file should be enough.



来源:https://stackoverflow.com/questions/38510050/q-object-or-not-q-object

标签
易学教程内所有资源均来自网络或用户发布的内容,如有违反法律规定的内容欢迎反馈
该文章没有解决你所遇到的问题?点击提问,说说你的问题,让更多的人一起探讨吧!