How to find sender in slot?

cerr

Hi,

I display a number of Checkboxes that get created in a loop and connected to a method like:

foreach(...) {
    box = DlgEnChckBxCrt("Enable", (Qt::CheckState)sttngs->value(grp+"/Enable").toInt());
    bool rv = QObject::connect(this->box, &QCheckBox::clicked, [&] { this->DlgEnChckSv(); });
}
QCheckBox* scaper::DlgEnChckBxCrt(QString txt,Qt::CheckState chckd) {
        QCheckBox *box = new QCheckBox(txt);
        box->setCheckState(chckd);
        return box;
}

Now in DlgEnChckSv I need to figure out, which checkbox got clicked, I have tried the following which has failed:

void scaper::DlgEnChckSv(void) {
    QCheckBox *src = qobject_cast<QCheckBox*>(sender());
    if (src)
        dbg_prnt << "inside " << __func__ << " for " << src->text().toStdString() << std::endl;
    else
        dbg_prnt << "no object found" << std::endl;
}

Why does this not work as expected and how do I do it correctly?
Thank you!

dheerendra

Just check this post

cerr

Okay,

So I've figured out that I need to use a variable in the current stack scope to work with lambda, i.e. I got it working with something like:

QCheckBox *tmpbox = nullptr;
foreach(...) {
    box = DlgEnChckBxCrt("Enable", (Qt::CheckState)sttngs->value(grp+"/Enable").toInt());
    tmpbox = box;
    bool rv = QObject::connect(this->box, &QCheckBox::clicked, [tmpbox,this] { this->DlgEnChckSv(); ;dbg_prnt << "senderObject: " << tmpbox->text().toStdString() str.toStdString() << std::endl;});
}

But I'm now wondering how I can distinguish them from each other as they all have the same label "Enable", I need to diustinguish them by grp how would I do so?

I tried tmpbox->name() but that doesn't work...

jsulm

@cerr You should rather use https://doc.qt.io/qt-5/qsignalmapper.html

cerr

What about it saying:
This class is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code. ?
I guess using lambda is its replacement, by passing the string text directly to the slot as argument - I thought I read that this shouldn't be done somewhere else... (missing the reerence)

ButtonWidget::ButtonWidget(const QStringList &texts, QWidget *parent)
    : QWidget(parent)
{
    QGridLayout *gridLayout = new QGridLayout;
    for (int i = 0; i < texts.size(); ++i) {
        QString text = texts[i];
        QPushButton *button = new QPushButton(text);
        connect(button, &QPushButton::clicked, [=] { clicked(text); });
        gridLayout->addWidget(button, i / 3, i % 3);
    }
    setLayout(gridLayout);
}
```

jsulm

@cerr This is the answer: "This class was mostly useful before lambda functions could be used as slots." :-)
Use lambda functions as you already do.

"I need to diustinguish them by grp" - what is grp?
"I tried tmpbox->name() but that doesn't work..." - did you set names before?

cerr

@jsulm said in How to find sender in slot?:

@cerr This is the answer: "This class was mostly useful before lambda functions could be used as slots." :-)

Yup,

I've figured this out by now as well. I'm still new to Lambda and am learning as I go...!

Use lambda functions as you already do.

"I need to diustinguish them by grp" - what is grp?

grp is a string that I used above in sttngs->value(grp+"/Enable") - that's how I distinguish the "Enables" from each other

"I tried tmpbox->name() but that doesn't work..." - did you set names before?

No I had not but it would give me a compiler error: ‘class QCheckBox’ has no member named ‘name’ after I had tried to access it with box->name()

Got it working fine now! Thanks for your help! :)

cerr

@julm I still have another question my friend, I did not get it working entirely the way I intended:
When I create my buttons in this fashion:

foreach(const QStringList  grp, groups) {
    box = DlgEnChckBxCrt("Enable", (Qt::CheckState)sttngs->value(grp+"/Enable").toInt());
    tmpbox = box;
    bool rv = QObject::connect(this->box, &QCheckBox::clicked, [tmpbox,this] { this->DlgEnChckSv(); ;dbg_prnt << "senderObject: " << tmpbox->text().toStdString() str.toStdString() << std::endl;});
}

grp will be a different value in every iteration as it calls the DlgEnChckBxCrt() function to create the QCheckBoxes but when a click triggers the lambda function in the connect() clause, grp will always just be the last value in the QStringList groups. So my question is, can I statically create the connect() linkage at the time QCheckBoxes get created too or how would I best go about this to have a connect for each value of grp?

cerr

I continue this in a new thread, the original problem has been resolved!
link to continuing thread: https://forum.qt.io/topic/105642/cn-i-find-the-layout-a-given-widget-is-a-member-of