How to properly use QLayouts (hbox, vbox, etc)? - c++

Question

I am building a custom widget based on QGraphicsWidget
Inside the widget, I need various other widgets in line with the size of the window. For this I am using
Layout = new QGraphicsLinearLayout();
Layout->setOrientation(Qt::Horizontal);
setLayout(Layout);
So I have a layout, and on each side of the layout I have a widget. So a widget on the left side, and a widget on the right side.
QGraphicsLinearLayout() below
500 px wide x
|--------------------------------|
| |
|left widget right widget| 100 px tall y
|--------------------------------|
I want the behaviour that when the window gets bigger, the widgets stay within x pixels of the edge. So if the window were to be resized to 10,000 pixels wide, left widget would always be 1 pixel from the left edge and right widget would always be 1 pixel from the right edge.
10000 px wide x
|---------------------------------------------------|
| |
|left widget right widget| 100 px tall y
|---------------------------------------------------|
The current behaviour is that left widget will stay in place and never move, and right widget will move away from the right edge.
To achieve this behaviour, I have tried the following:
Layout->setAlignment(leftWidget, Qt::AlignLeft);
That does absolutely nothing.
I also tried
Layout->addItem(leftWidget);
Layout->setStretchFactor(leftWidget, 0);
Layout->addItem(rightWidget);
Which gives the desired effect but overlaps the rightWidget with the border like so
500 px wide x
|--------------------------------|
| |
|left widget right widget 100 px tall y
|--------------------------------|
So how can I get my desired behaviour? QLayouts seem very confusing and the API's misleading thus far.

Answer 1

Solution
Use QGraphicsLinearLayout::addStretch between the left and right widgets in order to keep them to the sides and QGraphicsLayout::setContentsMargins to add a space between the widgets and the edges:
auto *l = new QGraphicsLinearLayout();
l->addItem(leftProxy);
l->addStretch();
l->addItem(rightProxy);
l->setContentsMargins(25, 1, 1, 1);
l->setSpacing(1);
Example
I have prepared a minimal example for you of how to use the proposed solution:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)
{
auto *view = new QGraphicsView(this);
auto *widget = new QWidget();
auto *leftWidget = new QPushButton(tr("Left"));
auto *rightWidget = new QPushButton(tr("Right"));
auto *leftProxy = new QGraphicsProxyWidget();
auto *rightProxy = new QGraphicsProxyWidget();
auto *l = new QGraphicsLinearLayout();
auto *sizeGrip = new QSizeGrip(widget);
leftWidget->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Expanding);
rightWidget->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Expanding);
widget->setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);
widget->setMinimumSize(sizeGrip->sizeHint().width()
+ leftWidget->sizeHint().width()
+ rightWidget->sizeHint().width(),
leftWidget->sizeHint().height());
leftProxy->setWidget(leftWidget);
rightProxy->setWidget(rightWidget);
l->addItem(leftProxy);
l->addStretch();
l->addItem(rightProxy);
l->setContentsMargins(25, 1, 1, 1);
l->setSpacing(1);
view->setScene(new QGraphicsScene(this));
view->scene()->addWidget(widget)->setLayout(l);
widget->resize(400, 200);
setCentralWidget(view);
resize(640, 480);
}