how to clear a QPlainTextBox within a QTabWidget?

[mzimmers]

Hi all -

I have a QTabWidget with four tabs, each containing a QPlainTextBox. How do I go about erasing the contents of the active tab? I've created a slot:

void Widget::on_pushButtonClear_clicked()
{
    int i;
    i = ui->tabWidget->currentIndex();
}

...but I can't figure out how to:

1. use this index to reference the active tab,
2. clear a QPlainTextEdit (thought this would be easy, but didn't see anything in the page).

Thanks for any guidance...

[SGaist]

Hi,

If the QPlainTextEdit is the widget set on the tab, you can use QTabWidget::currentWidget and qobject_cast to cast the pointer to the correct class and then call clear.

[mrjj]

Hi
Why not simply remove whole tab instead of "cleaning it"
http://doc.qt.io/qt-5/qtabwidget.html#removeTab

ui->tabWidget->removeTab ( ui->tabWidget->currentIndex() );

and
ui->plainTextEdit->clear();

[mzimmers]

@mrjj I want to keep the tab because more stuff will be written to it. Clearing the contents is just a convenience for the user.

[mrjj]

@mzimmers
Ok, but is the page the actual plainTextEdit or does it have a parent QWidget?
(as @SGaist asks)

[mzimmers]

This is how I did it (but I'd be happy to change it if it would make this easier):

[mrjj]

@mzimmers
Ok so its not the page itself.
Well, calling clear() on PlainTextWidget should make you happy.

[mzimmers]

I'm afraid I don't understand. How do I know which one to call the clear on? In other words, what do I do with the index that denotes which tab is displayed?

[SGaist]

You don't need it, as I suggested, you can get the widget directly.

[mzimmers]

@SGaist right, I can do this:

    QWidget *w ;
...
    w = ui->tabWidget->currentWidget();

But what member/method of w gives me the child QPlainTextBox? That's the step I'm missing.

[mpergand]

The QPlainText should be the first child.

But, why not put the QPlainText directly as the tab widget ?

[mzimmers]

@mpergand I don't know how to do that, at least not with Designer.

But this seems to work, though I'm not sure it's what SGaist had in mind:

void Widget::on_pushButtonClear_clicked()
{
    QWidget *w ;
    QPlainTextEdit *qpte;

    w = ui->tabWidget->currentWidget();
    qpte = qobject_cast<QPlainTextEdit *>(w->children().at(0));
    qpte->clear();
}

Comments?

[mpergand]

In Designer, it seems impossible to change the default widget added automaticaly.
I'm missing something ?

[mrjj]

@mpergand
I think not. Only way i found was via promotion.

[mrjj]

@mzimmers

Just in case u call on_pushButtonClear_clicked twice..

if ( w->children().size() ) {
qpte = qobject_cast<QPlainTextEdit *>(w->children().at(0));
...
}

[mpergand]

@mrjj
Infortunately, you cannot promote to an already existing widget, QPlainTextEdit here.
A pity ...

[mzimmers]

Got it. Thanks for the assistance; perhaps the best lesson here is that there are still things one can't do in Designer.

[mrjj]

@mzimmers
Well its pretty easy to setup in code if really needed.
I often mix both UI design and code.
Thats what i like the best with Qt. Its not either WYSIWYG and no code
or reverse. Its actually only code. ;)

[J.Hilk]

@mzimmers said in how to clear a QPlainTextBox within a QTabWidget?:

void Widget::on_pushButtonClear_clicked()
{
    QWidget *w ;
    QPlainTextEdit *qpte;

    w = ui->tabWidget->currentWidget();
    qpte = qobject_cast<QPlainTextEdit *>(w->children().at(0));
    qpte->clear();
}

because this is bound to fail as soon as the first child is not the targeted widget, or if it does not have children at all, I would suggest the following change:

void Widget::on_pushButtonClear_clicked()
{
    QWidget *w ;
    QPlainTextEdit *qpte;

    w = ui->tabWidget->currentWidget();
    for(QObject *obj : w->children()){
         qpte = qobject_cast<QPlainTextEdit *>(obj);
         if(qpte)
              qpte->clear();
    }   

[SGaist]

No need to make it so complicated: findChild is what you are looking for.

QWidget *w = ui->tabWidget->currentWidget();
QPlainTextEdit *qpte = w->findChild<QPlainTextEdit *>();
if (qpte) {
    qpte->clear();
}

Since the content of the widget is known, there's no real need for the if, it's to show good practice if you are doing "widget inspection".