Qt - 每次调用 show() function 时，如何将信号连接到 QGroupBox？

Question

I have two classes that are interacting with each other, let's call them for the sake of simplicity ClassA and ClassB . In ClassA , I would like to emit a signal when a specific QGroupBox is shown that triggers a slot in ClassB to set the given channel's checkbox.

I have a code that consists of several thousand lines, so I included only the most relevant parts.

ClassA header

private:
QGroupbox* m_Channel1GroupBox;
void setup();

signals:
void setCheckBox(int, bool);

ClassA source

void ClassA::setup()
{
    m_Channel1GroupBox = new QGroupBox("Channel 1", this);

    connect(m_Channel1GroupBox, &QGroupBox::show, [this]()
    {
        emit setCheckBox(1, true);
    });
}

ClassB header

private:
QCheckBox* m_Channel1CheckBox;

public slots:
void setCheckBox(int, bool);

ClassB source

void ClassB::setCheckBox(int channel, bool check)
{
    if (channel == 1)
    {
        m_Channel1CheckBox->setChecked(check);
    }
}

Main.cpp

connect(m_ClassA, &ClassA::setCheckBox, m_ClassB, &ClassB::setCheckBox);

The lambda expression compiles, but unfortunately it doesn't do what it is expected to do, which is whenever m_Channel1GroupBox->show() is called, then tick the checkbox of Channel1. Actually this block of code never executes, which would emit setCheckBox .

Please note that the setCheckBox function works perfectly when called in another function of ClassA and it checks or unchecks the desired channel in ClassB . This is possible using another connect in the Main.cpp file where the object instances are created.

Answer 1

run the code and you will see that the

QGroupBox has no signal to emit called show ... show is actually a slot

QObject::connect: signal not found in QGroupBox

But... if you are calling show per hand, then emit the signal right after that...

Answer 2

You will need to subclass QGroupBox to achieve the functionality you require.

Override QWidget::showEvent(QShowEvent*) in your QGroupBox subclass and do the work there.

Please see the documentation for QWidget .