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c++qtsignals-slots

why append Slot doesn't work?

I have got a problem when I try to make following simple connections

QSpinBox *spinBox = new QSpinBox;
QSlider *slider = new QSlider(Qt::Horizontal);
QTextEdit *text = new QTextEdit("Hello QT!");

QObject::connect(spinBox, SIGNAL(valueChanged(int)),slider, SLOT(setValue(int)));
QObject::connect(slider, SIGNAL(valueChanged(int)),spinBox, SLOT(setValue(int)));
QObject::connect(slider,SIGNAL(valueChanged(int)),text, SLOT(append("slider changed!")));
QObject::connect(spinBox,SIGNAL(valueChanged(int)),text, SLOT(append("spinbox changed!")));
QObject::connect(text,SIGNAL(textChanged()),spinBox,SLOT(clear()));

It can be successfully compiled and excuted.But the two append slots seem not work.I've checked the help manual about QTextEdit and there's a public slot append there.Have I missed something?Help would be appreciated!

Solution

  • Unfortunately, you cannot pass custom values to your slots via QObject::connect (only type information for the arguments is allowed/interpreted correctly). Instead, create your own slot, something like

    void MyWidget::mySliderChangedSlot(int newValue)
{
  text->append("slider changed!");
}

    and use

    QObject::connect(slider, SIGNAL(valueChanged(int)), pMyWidget, SLOT(mySliderChangedSlot(int)));

    to achieve your desired behaviour.

    I hope that helps.