Is there a way to get the expected size of a component?

[kermitfrog]

My case: I need a ComboBox, but when trying make the drop-down-popup part using a PopupWindow & StandardListView, I can't get the size right.
What I need is something like this:

height: min(300px, root.model.length * StandardListViewItem.height);

Can this be achieved somehow in a way that will work regardless of rendering backend and the users font settings?

[ogoffart]

you can use the preferred-height property.

[kermitfrog]

Thanks for the answer, but I don't understand how that would help. Maybe I share some current code:

export component SearchBox {
    in property <[StandardListViewItem]> model;
    in-out property <string> current_text;
    callback filter(string);

    text:= LineEdit {
        width: 100%;
        text: current_text;
        changed text => {
            current_text = self.text;
            filter(self.text);
            if (root.model.length >= 1 && root.model[0].text != self.text) {
                results_popup.show();
            }
        }
    }

    results_popup:= PopupWindow {
        x: 0;
        y: text.y + text.height;
        forward-focus: text;
        width: root.width;
        height: min(300px, (root.model.length + 1) * (text.height - 1px)); // approximation; way too large
        Rectangle {
            background: Palette.alternate-background;
            listview:= StandardListView {
                model: root.model;
                current-item-changed(current-item) => {
                    text.text = root.model[current-item].text;
                    results_popup.close();
                }
            }
        }
    }
}

• replacing height: min... with preferred-height does not make a difference.
• listview.preferred-height is 0, so that does not help either.
• Actually writing height: min(300px, (root.model.length + 1) * StandardListViewItem.preferred-height); leads to error: Cannot access id 'StandardListViewItem'

EDIT: meanwhile I reread the documentation on "Positioning & Layouts". If I understand it correctly, listview.preferred-height should work because its computed from it's children and it beeing 0 (despite having >0 children) is a bug. Or did I do something to prevent the computation?

[ogoffart]

Right, it was meant to be listview.preferred-height, but it looks like it doesn't have the right value, I'd say this is a problem in the implementation of StandardListView.

[kermitfrog]

I think the problem is in ScrollView.

If I change from StandardListView to ListView, I still get a preferred-height of 0. Same with

            listview:= ScrollView { 
              VerticalLayout {
                for item in model: Text {
                    text: item.text;
                    height: 20px;
                }
             }
          }

Are you already creating an issue, or shall I?