Objects and connect

pixbyte

In my code I try to receive the name of the control where the text input occour.

For this I use:

QObject::connect( cdTextArrangerEdit, &QLineEdit::textChanged, this, &MainWindow::onEnterCDTextText );

and the function:

void MainWindow::onEnterCDTextText(QString strText)
{
    qDebug() << sender()->objectName();
}

But I always recive an empty qDebug string. My idea was to receive the name "cdTextArrangerEdit". Is there anything I missunderstood?

koahnig

@pixbyte

Try to set an object name for the object.

According to https://doc.qt.io/qt-5/qobject.html#objectName-prop the default name is an empty string.

Christian Ehrlicher

So where do you set your object name to the one you expect?

wrosecrans

Do you ever set the object's name? You won't get the name of an object that you used in the C++ source -- you only get a name explicitly set with setObjectName(). C++ doesn't allow that sort of introspection automatically.

JonB

@pixbyte
By default there would be no object name set. To do it this way you would need to use setObjectName() to have set the name previously.

Consider instead of sender() using a lambda connection, like:

QObject::connect( cdTextArrangerEdit, &QLineEdit::textChanged,
                  this, [cdTextArrangerEdit, this](const QString &strText) { onEnterCDTextText(cdTextArrangerEdit->objectName(), strText); } );

// or, you might want to pass the literal name here:
QObject::connect( cdTextArrangerEdit, &QLineEdit::textChanged,
                  this, [this](const QString &strText) { onEnterCDTextText("cdTextArrangerEdit", strText); } );

void MainWindow::onEnterCDTextText(const QString &objectName, const QString &strText)
{
    qDebug() << objectName;
}

You can do more things with lambdas than via sender(), which also has issues.

Pablo J. Rogina

@pixbyte you may want to check this document to see how they're printing the object name.

Pl45m4

@pixbyte said in Objects and connect:

My idea was to receive the name "cdTextArrangerEdit". Is there anything I missunderstood

Yes!
objectName != name of your variable

The objectName is a (not only) Qt specific thing. You can give every QObject its own unique name.
QObjects you create in QtDesigner have a default name, others don't. So you have to set one.

Having a QLineEdit created in Designer before,

this

    QLineEdit * lineEd = new QLineEdit(this);
    qDebug() << ui->lineEdit->objectName();
    qDebug() << lineEd->objectName();

prints:

"lineEdit"
""