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:

use this index to reference the active tab,
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".