How can I create a QVector or other container which can contain different widgets?

Question

I am developing a GUI with Qt5, and in the main window of this GUI, it contains at least 4 tab widgets, and each tab widget will contain serval different child QWidgets, such as QLineEdit, QSpinBox, QLCDnumber, etc. Then when I open the tab, all its child widgets will appear.

Thus, for each tab, I decided to create a QVector(or another container type) to contain its all child Widgets,e.g.:

QVector<QWidget*> wids;

for the first tab widget, if it has the following children:

QLineEdit* line=new QLineEdit(this);
QLCDNumber* lcd=new QLCDNumber(this);
QSpinBox* spn=new QSpinBox(this);

then somehow I would like to do

wids.append(line);
wids.append(lcd);
wids.append(spn);

and next,I want to operate each widget inside the tab,e.g.:

wids[0]->setText("good");
wids[1]->display(1);
wids[2]->setRange(0,10);

I know I need to use dynamic_cast<...>, but I DO NOT KNOW how to do that,is ther anyone could give me some advice?

many thanks!

"I know I need to use dynamic_cast". When you knpw that, you know that your design is broken and it's time to re-think it. Why do you need a vector of widgets in the first place? — n. 1.8e9-where's-my-share m.

Hafnernuss Hafnernuss · Accepted Answer · 2019-10-23T08:36:54

QLineEdit, QLCDNumber and QSpinBox already inherit from QWidget. So if you put those in a QVector (or any container for that matter, could be a std::vector<QWidget*>) you have to deal with QWidget pointers.

As you correctly stated:

wids.push_back(line);
wids.push_back(lcd);
wids.push_back(spn);

To get your respective classes back, for example QLineEdit back, you need to downcast from QWidget to QLineEdit, QLCDNumber or whatever else inherits from QWidget.

QLineEdit * line = dynamic_cast<QLineEdit*>(wids[0]);

This of course assumes that you know exactly at which position the object is located. You can of course test if your cast was successful:

if( line == nullptr )
{
    // cast failed, either wids[0] is invalid or does not derive from QWidget
}

else
{
    // cast was successful, use 'line' as regular QLineEdit.
}

A one-liner, although being quite unsafe, would be:

dynamic_cast<QLineEdit*>(wids[0])->setText("myText");

How can I create a QVector or other container which can contain different widgets?

1 Answers