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How to get rid of changed code lingering in the moc?

  • In my main menu, I had an action set up and its accompanying code. Then I decided to change the action name on the menu to something else. I did that and took the code from the first, no-longer-needed action and gave it to the new action. Now I get this each time I run it:

    QMetaObject::connectSlotsByName: No matching signal for on_actionA_lter_triggered()

    I've tried to "Clean" the build, thinking that would cure the moc's ailment, but no dice. So what can I do to fix this? This is the ONE thing about Qt that drives me crazy.

  • Lifetime Qt Champion

    hi @landslyde

    you most likely still have the slot function in you code, but the signal no longer exists.

    that's what the connect error message is going to tell you.

  • I've tried taking it out. That only throws an error in the moc. I'll post this.

    Code commented out:

    //void MainWindow::on_actionA_lter_triggered()

    Error thrown in the moc:

    /home/slyde/Desktop/Qt/build-Qt_Stacked_Widget-Desktop_Qt_5_11_0_GCC_64bit-Debug/moc_mainwindow.cpp:100: error: undefined reference to `MainWindow::on_actionA_lter_triggered()'

    The error code:

    void MainWindow::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
        if (_c == QMetaObject::InvokeMetaMethod) {
            MainWindow *_t = static_cast<MainWindow *>(_o);
            switch (_id) {
            case 0: _t->on_actionE_xit_triggered(); break;
            case 1: _t->on_actionA_lter_triggered(); break;  // throws error here
            case 2: _t->on_action_Add_triggered(); break;
            case 3: _t->on_action_Delete_triggered(); break;
            case 4: _t->on_action_View_triggered(); break;
            case 5: _t->on_action_Search_triggered(); break;
            case 6: _t->on_btnCancel_add_recipe_clicked(); break;
            case 7: _t->on_action_Edit_triggered(); break;
            default: ;

    I can comment out that line "case 1:" and I go back to getting a warning. There has to be a way for this to be cleaned out of the code. I know I'm not the first person that's ever changed his mind on the name of something.

  • Fixed it. Thank you, aha_1980.

  • Lifetime Qt Champion

    Hi @landslyde,

    glad you figured it out.

    Running Qmake most often helps, in very rare cases you need to delete your build folder to get the error away.

  • Actually, while I'd deleted the action code from mainwindow.cpp, I hadn't deleted its prototype in mainwindow.h. That's what the compiler was complaining about. So I deleted it in the .h and then ran Build -> Clean All. Doing that removed the reference to the deleted action in the moc file. Problem solved. Thanks again for your help.

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