Question

I’m relatively new to Qt; I’m writing a small program and I don’t want to get into making my own classes for each widget and such. So far I haven’t had many difficulties, but I’m slightly confused about signals and slots. I want to make a signal that triggers when a user types into a text box (QLineEdit) and presses enter. I would prefer the slot to be a function that accepts the text inputted by the user.

So far I’ve come up with this:

textBox.connect(&textBox,SIGNAL(textBox.returnPressed()),/*What to put here?*/,processText(/*Here?*/))

I apologize if this piece of code is terribly wrong; as I said I’m relatively new to Qt.

Help would be very much appreciated.

Answer 1

Sadly, I don’t think there is a way to achieve this without inheritance – if you want the text to go with the signal or some custom handling to be done in the slot that is called.

If not, you can just use the “returnPressed” signal emitted from the QLineEdit and some pre-existing slot I couldn’t possibly know.

Here’s my solution using inheritance.

To make your own slot, you need to make an inherited class. Inherit it from Qobject, directly or indirectly.

//myClass.h
#ifndef myclass_h_
#define myclass_h_
#include <QObject>

class myClass: public QObject
{
    // important
    Q_OBJECT;

    ....
    public slots:
        void takeText(QString p_value);
};

#endif

And to get a signal like that from a QLineEdit, you need something custom as well

//myLineEdit.h
#ifndef mylineedit_h_
#define mylineedit_h_
#include <QLineEdit>

class myLineEdit: public QLineEdit
{
    // important
    Q_OBJECT;

    ....
    public slots:
        void handleReturnPressed();

    signals:
        void newText(QString p_value);
};

#endif

And then do these

myLineEdit::myLineEdit()
{
    connect(this, returnPressed(),
            this, handleReturnPressed());
}

void myLineEdit::handleReturnPressed()
{
    emit(newText(text());
}

After this, create a myClass object, and connect the signal to it.

myClass * thing = new myClass();
myLineEdit* lineEdit = new myLineEdit();

connect(lineEdit, SIGNAL(newText(QString),
        things, SLOT(takeText(QString));