Qt alignment in QGridLayout eliminates the resizing of its elements

Question

Ok, so basically I have a simple table with a QWidget and two buttons as shown below:

QGridLayout *layout = new QGridLayout;
layout->addWidget(viewcontainer,0,0,1,2);
layout->addWidget(reset,1,0);
layout->addWidget(done,1,1);

This is basically what I want, where "reset" and "done" are buttons. Essentially it's a QWidget, viewcontainer, which resizes as the window size is changed by the user while the buttons' heights remains the same. But, the default for the gridlayout is to align the contents to the left. If I change this with:

layout->addWidget(viewcontainer,0,0,1,2, Qt::AlignCenter);

It does sort of what I want, but the graphicsscene no longer resizes (remains a small constant size). I'd like to retain the resizing while just aligning the widget to the center. Thanks.

score 4 · Accepted Answer · answered May 30 '12 at 15:08

I think the easiest solution which provides a clean solution is to nest 2 layouts.

Your 'outer' (parent) layout should be a QHBoxLayout and you can add your QGridLayout into it as an 'inner' (child) layout with addLayout().

Based on my experience you should avoid to set Qt::Alignment every time you can. It can really mess up your layout. For simple layouts it can work but for more complex ones you should avoid it. And you never know that you should extend your layout in the future or not so my suggestion is to use nested layouts.

Of course you can create a QWidget for the 'outer' layout and for the 'innser' layout as well but most of the times it should be fine to just nest 2 layouts.

Also you can use QSpacerItem to fine-tune your layout.

I sort of skipped this problem and will come back to it in a few days. Just saw your comment and will try it out. Thanks — JustinBlaber, Jun 08 '12 at 15:21

score 2 · Answer 2 · answered May 29 '12 at 06:09

2

Have a look at this example code, I think it does what you want:

#include <QApplication>
#include <QPushButton>
#include <QGraphicsView>
#include <QGridLayout>
#include <QPalette>

class MyWidget : public QWidget
{
public:
   MyWidget()
   {
       QGridLayout * layout = new QGridLayout(this);

       QGraphicsView * gv = new QGraphicsView;
       layout->addWidget(gv, 0,0, 1,2);
       layout->setRowStretch(0, 1);  // make the top row get more space than the second row

       layout->addWidget(new QPushButton("reset"), 1,0);
       layout->addWidget(new QPushButton("done"),  1,1);
   }
};

int main(int argc, char ** argv)
{
   QApplication app(argc, argv);

   MyWidget w;
   w.show();
   return app.exec();
}

answered May 29 '12 at 06:09

Jeremy Friesner

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This didn't work. When I set Qt::AlignCenter, the top cell does take up all the "row space" but the widget inside that cell is a fixed size (and in the center of the cell), whereas before the widget inside the cell would resize to the cell itself. – JustinBlaber May 29 '12 at 14:22
Don't set Qt::AlignCenter. Does the resizing work properly if you just compile the above code verbatim? If so, then it's a matter of figuring out what is different between your viewcontainer widget and the QGraphicsView widget in the example. You might try doing a setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored) on your widget as well, to see if that will convince it to become larger. – Jeremy Friesner May 29 '12 at 15:48
Yea I guess I should have specified this but I want the widget to keep a certain aspect ratio using this code: void roilayout::resizeEvent(QResizeEvent *event) { QSize p(roiview->refimage->size()); p.scale(viewcontainer->size(), Qt::KeepAspectRatio); viewcontainer->resize(p); } . (Sorry about format - I dont know how to format comment code). But yea, when it resizes, it aligns to the left. – JustinBlaber May 29 '12 at 17:24
Instead of trying to call resize() on your widget, you might try overriding the QWidget::heightForWidth(int) method of the widget, so that it always returns a height that has the correct aspect ration for the width passed in as the argument. – Jeremy Friesner May 29 '12 at 21:33

Qt alignment in QGridLayout eliminates the resizing of its elements

2 Answers2