Qt Desktop on Mac: QFormLayout sizing with subpanels - c++

Question

TL;DR: I'm having a grow/shrink probably using embedded forms inside a MainWindow. I'm unsure what to try next.
Okay, I have another sizing problem.
This is a sample app of what I'm trying to do:
When I click on the various toolbar options, I intend to change the central widget contents accordingly. Maybe I should just use a tab widget, but I wanted to do it this way.
In the simplest form, with a widget layout like this:
I set the central widget's layout to Horizontal, and the Inner Widget to FormLayout then set the inner widget's expand rules to expand any expandable fields. As I resize the window, the simple line edit expands and contracts as desired.
When I click the bus icon in the toolbar, I swap out the contents of the central widget with a separate panel. That panel has a widget with a form layout, and is also set to expand and collapse. Here are the layout rules for the second panel:
My trigger code does this:
currentCenter = ui->innerWidget; // In the constructor
currentCenter->hide();
if (v1Form == nullptr) {
v1Form = new V1Form(ui->centralWidget);
}
v1Form->show();
currentCenter = v1Form;
I have tried various orders to this, and I tried using setCentralWidget(). In all cases, the new central area remains a fixed size, even though the original one expands and collapses.
What is working: I can readily change the inner contains for different forms. That's working great. (It took a while to figure it out.)
-or- I can make simple popup forms that grow and shrink properly.
What is not working is grow/shrink when I embed my form inside my central widget or if I use setCentralWidget.
I'm not sure what else to try.

Answer 1

Maybe I should just use a tab widget, but I wanted to do it this way.
You should definitely use a QTabWidget as your central widget. It is designed specifically for your use case, and it will greatly simplify your code.
My trigger code does this:
currentCenter = ui->innerWidget; // In the constructor
currentCenter->hide();
if (v1Form == nullptr) {
v1Form = new V1Form(ui->centralWidget);
}
v1Form->show();
currentCenter = v1Form;
With a QTabWidget, your trigger code can be simplified to:
ui->innerTabWidget->setIndex(1).
You don't need to dynamically construct a V1Form. Simply use Qt Designer to create multiple pages in your QTabWidget and implement all your subpanel widgets within your MainWindow.ui.
(Nonetheless, if you want to implement each subpanel in its own separate *.ui file, you can still promote each page in your QTabWidget to your custom widget.)
What is not working is grow/shrink when I embed my form inside my central widget or if I use setCentralWidget.
To address your original symptoms: Your widgets don't grow/shrink because you didn't put them inside a layout that is part of your main window.

Answer 2

I found a solution doing it the way I started. I had to add one line of code:
void MainWindow::switchForm(QWidget *widget) {
if (centralForm != widget) {
if (centralForm != nullptr) {
centralForm->hide();
centralForm = nullptr;
}
if (widget != nullptr) {
centralForm = widget;
centralForm->show();
ui->centralwidget->layout()->addWidget(centralForm);
}
}
}
void MainWindow::on_actionSetup_triggered()
{
if (setupForm == nullptr) {
setupForm = new SetupForm(ui->centralwidget);
}
switchForm(setupForm);
}
The missing line -- adding my new form to the layout:
ui->centralwidget->layout()->addWidget(centralForm);