@Hai-Anh-Luu Welcome to the forum.

Until the widget is displayed its size, and the size of any child widget in a layout, is unknown. In the widget class constructor^^ the widget is not yet shown so you get either the size hint from the widget concerned or some other value.

^^ That is when executing this line window = NewGrid()

One way to see the size that is initially allocated is to do so in a slot connected to a zero-length (or very short) single-shot QTimer. This will fire when the event loop is reached, after the UI is shown. That is when app.exec() is running.

Kind of solved. If I set sizeAdjustPolicy to AdjustToContents and sizePolicy to Maximum, the list widget size will adjust to accomodate items plus small margins around them. I'm quite happy with the result, it would be even better if I could make items equally distribute across available space, but even now it looks good enough.

Hello again,

I managed to fix the issue. I simply moved all my QAction objects to the other QToolBar since the designer did not allow me to reposition the tool bars.

Thank you again.

@TUStudi

Try a cascading horizontal + vertical layout for your page. Could be an issue with the stretch of the last column, where your green button lives or the QGridLayout in general.

Edit:
Yeah, that's probably it.
Gridlayouts can have "empty" cells... Your two groupBoxes with your options take two cells above the button, which takes one, but expands to full size. As soon as you hide the content (grpBox 2nd opt) of second column, the gridLayout only has three rows (grpBx radio, grpBx first, green btn), but the QGridLayout won't delete its second column, but will leave it just empty and this takes some (little) space. Probably exact that amount of space, the green button expands to the right (aligning to the outter border of your grid).

So try horizontal + vertical layouts or check, if there really is some empty cell (which should be, since you don't take the widget but just hide it).

QGridLayout::columnCount() should return (at least) 2 when your app is in "small" mode (and also 2 or 3 when you switch to "big")

@JonB
I am passing to QML for this reason. There, placement and dimensioning of graph oblect is very easy to do. I like also the stong division between frontend a nd backend!!!

You're correct and that's a good question. What version of Designer are you using ?

@jsulm
I got this, thanks

@VRonin said in I can't figure out what size polices to use to get widgets laid out the way I want:

what layouts are you placing in this widget?

I'm using QGridLayout

Can you run a little test ?

What do you get if you call qDebug() << yourToolBox->sizeHint(); before and after it's shown ?

very cool. I like it!

thanks again

The thing is that toolbars don't really display icons. They display widgets (that can have icons). By default when you add an action to a toolbar a QToolButton is created for it, but you are not limited to that and can add any widget e.g. an expanding line edit, combobox or a button with an icon and text. All of these can have different size policies, be expanding or have a custom stylesheet applied.
All of this makes calculating such size not feasible because how would you calculate it if a widget can change its size.

What I'm saying is that yours is a special, very specific case (with just icons), and as such you need to handle it yourself if you want to.

To answer your questions:

It's not one thing that adds the space. There are couple of aspects that can contribute. You can control some(or all?) of them with stylesheets e.g. set padding of the toolbar and toolbuttons to 0 and margins and borders of the toolbuttons. By default all of these depend on a style and will vary across computers. You also need to be careful to consider the size of the toolbar handle (if it's movable) as its size depends on the active style. You also need to consider that if the icon is narrower than the iconSize then there's gonna by space left anyway. nope, AFAIK it can vary from one item of the toolbar to another if you set it this way nope and just out of curiosity - why do you need that? The bar will display an arrow button that will let you see the overflowing items. Also such calculated size would be useless as the window can be resized and thus the toolbar too (unless you're doing some really fancy layout).

Read about

QWidget::setSizePolicy();

Solution here if anyone runs into the same problem: http://stackoverflow.com/questions/30672183/square-custom-qwidgets-inside-qgridlayout-inside-qscrollarea

Hi, this is old now but in case someone else finds this:
I managed to solve this problem by using
setSizeConstraint(QtWidgets.QLayout.SetNoConstraint)
for a layout holding the QLineEdit widget. Actually it wasn't the layout holding the widget, but the layout holding that layout, so you may need to experiment to find out where you need to make this update (or just use SetNoConstraint for all your layouts)
I hope this helps someone!