How to properly size Qt widgets?

Question

Main Question

What is the "right" way to give your widgets default sizes and make sure they contract, expand, or remain fixed if there is additional or not enough space to accommodate them?

How I Think Qt Works

After reading the Qt documentation it seems like the sizing algorithm goes something like this...the layout begins by asking its children for their ideal size via the QWidget::sizeHint method. If the layout has additional space or not enough space then it'll determine which widgets to resize based on each widget's sizing policy (QWidget::sizePolicy), minimum size (QWidget::minimumSize), and maximum size (QWidget::maximumSize).

Why isn't there a QWidget::setSizeHint method?

If my understanding is close to being accurate then it would seem all you'd have to do is set the sizeHint, sizePolicy, maximumSize, and minimumSize on each widget and everything would just work. So why isn't there a setSizeHint method?!?!??!! Sure, every time you use a widget that provides all of the functionality you need (QTableView, QComboBox, etc) you could extend it and override a single method but that sounds absolutely ridiculous.

One of the sizing issues I'm fighting with.

I've got a QMainWindow with a QDockWidget on the left hand side. The QDockWidget has a QTableView. I'd like to have the QDockWidget/QTableView take up a "reasonable" amount of space on start up and then the user can resize it however small or large they'd like.

Unfortunately, when the application starts up it gives the QDockWidget/QTableView so little space that it requires a horizontal scroll bar. The only way I've found to force it to give it a reasonable amount of width is to set the QDockWidget's minimum width but then it prevents the user from resizing it as small as they might like to.

Galeiform

You asked a lot of questions (and ranted a bit). What's your actual question here? – Retinoscopy

What is the "right" way to give your widgets default sizes and make sure they contract, expand, or remain fixed if there is additional or not enough space to accommodate them? ...specifically in my case when the default size falls in between the minimum and maximum or you don't want a min/max at all. – Galeiform

Consider cropping out some of the extraneous material in your post and focus on the question itself. – Retinoscopy

What version of Qt are you using? – Retinoscopy

I'm using Qt 4.8 (will upgrade in the not so distant future) and I reformatted/edited my post a bit so hopefully it is more inviting. – Galeiform

You may start here: doc.qt.io/qt-5/layout.html – Mukden

Answer 1

Why isn't there a QWidget::setSizeHint method?

In my opinion it is much better for a widget to compute its preferred size based on its content (or rules) instead of allowing the coder to set a sizeHint probably hardcoded or at least prone to errors.

I almost never had to set a size on a widget, playing with the QSizePolicy was enough. And when I needed some specific constraints, playing with minimum/maximum sizes was enough. So that Qt layouts were always able to adapt the widget.

If you want to set up yourself some percentages on the sizes etc, you can play with the stretch parameter. You can also add spacers when you need empty spaces.

Extending a QWidget to override the QWidget::sizeHint method does not sound ridiculous to me, as you change the widget behaviour by changing its preferred size and that fits the polymorphism spirit of OOD.

How to properly size Qt widgets? is a vague question and depends on the use cases. Most of the time choosing the good layouts and size-policy lets you achieve very adaptative GUI. Qt Designer can help to do this right, even if the layout management is not always intuitive (you need to place your widgets first and then set them in layouts from the inner to the outer layout).

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About your specific issue, it's hard to tell why your QDockWidget gets too small without knowing the details of the layout(s) you have around your two widgets in the window. Maybe it is a specific issue with QDockWidget : see related questions :

• QDockWidget starting size
• Qt 5.7 QDockWidget default size
• Prevent QDockWidget autosizing behaviour

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