How to connect the signal valueChanged from QLineEdit to a custom slot in Qt

Question

I need to connect the valueChanged signal from QLineEdit to a custom slot programatically. I know how to do the connection by using Qt Designer and doing the connection with graphical interface but I would like to do it programmatically so I can learn more about the Signals and Slots.

This is what I have that doesn't work.

.cpp file

// constructor
connect(myLineEdit, SIGNAL(valueChanged(static QString)), this, SLOT(customSlot()));

void MainWindow::customSlot()
{
    qDebug()<< "Calling Slot";
}

.h file

private slots:
    void customSlot();

What am I missing here?

Thanks

Lanfranc

Answer 1

QLineEdit does not seem to have valueChanged signal, but textChanged (refer to the Qt documentation for complete list of supported signals). You need to change your connect() function call too. It should be:

connect(myLineEdit, SIGNAL(textChanged(const QString &)), this, SLOT(customSlot()));

If you need the handle the new text value in your slot, you can define it as customSlot(const QString &newValue) instead, so your connection will look like:

connect(myLineEdit, SIGNAL(textChanged(const QString &)), this, SLOT(customSlot(const QString &)));

Doretheadoretta

Changed valueChanged to textChanged and static QString to const QString & and worked. I don't know how I missed that, specially static QString (wow), thanks a lot. Also thanks a lot for the second example since I was also wondering about the usage of the parameter. Thanks a LOT – Lanfranc

Here's Qt 5's new way to connect, connect(myLineEdit, &QLineEdit::textChanged, this, &MainWindow::customSlot); – Finalize

Answer 2

Here also with lambda if interested:

connect(myLineEdit, &QLineEdit::textChanged, [=](QString obj) { customSlot(obj); });

Row