CODEWITHSUNDEEP
c++qtscrollscrollbar
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Reputation: 2114

Fixed size widget in QBoxLayout in QScrollArea

I am developping a Qt application that run on full screen on an embedded system (BeagleBone Black with 4d 4.3'' touchscreen). I want to display a varying number of fixed width custom widget (let's say those are simple sliders for examples). So my thought was to have a QScrollArea, which I added to my form using Qt Designer, which take must of the space on my screen. Then, put the number of QSlider I want in a QHBoxLayout. And finally, display the QHBoxLayout in the scroll area. This way, I want a horizontal scroll bar to appear if the number of QSlider asked is to big to be displayed on the screen. I also want the QSlider to have a constant width (my custom widget has a fixed width). So this is the code I have written:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    // ui->scrollArea is a QScrollArea generated by Qt Designer
    ui->setupUi(this);
    QHBoxLayout * layout = new QHBoxLayout(ui->scrollArea);
    layout->setSpacing(1);
    QSlider * slider1 = new QSlider(layout->widget());
    QSlider * slider2 = new QSlider(layout->widget());
    QSlider * slider3 = new QSlider(layout->widget());
    QSlider * slider4 = new QSlider(layout->widget());
    slider1->setFixedSize(200, 200);
    slider2->setFixedSize(200, 200);
    slider3->setFixedSize(200, 200);
    slider4->setFixedSize(200, 200);
    layout->addWidget(slider1);
    layout->addWidget(slider2);
    layout->addWidget(slider3);
    layout->addWidget(slider4);
    ui->scrollArea->setLayout(layout);
}

The result gives a square box without any scroll bars and with overlapping sliders.

I tried to add:

slider1->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
slider2->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
slider3->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
slider4->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));

But same result.

So what's the proper way to display fixed size content in a fixed size scroll area?

Upvotes: 1

Views: 1630

Answers (1)

Puck
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Reputation: 2114

Alright, I found the response while writing the question, so as others seems to have the same problem, I post the solution with a complete example.
The solution is to pass by another QWidget before the QScrollArea, so it gives the following structures (with parent in brakets) [and type in square brakets]

ui->scrollArea [QScrollArea]
|\  
|  widget (ui->scrollArea) [QWidget]  
| |\  
| | layout (widget) [QHBoxLayout]  
| | |\  
| | | slider1 (layout->widget()) [QSlider]  
| | | slider2 (layout->widget()) [QSlider]  
| | | slider3 (layout->widget()) [QSlider]  
| | | slider4 (layout->widget()) [QSlider]

Which is implemented by the following code:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QWidget * widget = new QWidget(ui->scrollArea);
    QHBoxLayout * layout = new QHBoxLayout(widget);
    layout->setSpacing(1);
    QSlider * slider1 = new QSlider(layout->widget());
    QSlider * slider2 = new QSlider(layout->widget());
    QSlider * slider3 = new QSlider(layout->widget());
    QSlider * slider4 = new QSlider(layout->widget());
    slider1->setFixedSize(200, 200);
    slider2->setFixedSize(200, 200);
    slider3->setFixedSize(200, 200);
    slider4->setFixedSize(200, 200);
    slider1->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
    slider2->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
    slider3->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
    slider4->setSizePolicy(QSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed));
    layout->addWidget(slider1);
    layout->addWidget(slider2);
    layout->addWidget(slider3);
    layout->addWidget(slider4);
    widget->setLayout(layout);
    ui->scrollArea->setWidget(widget);
}

Upvotes: 1

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