StackLayout children have unpredictable widths

mzimmers

Hi all -

I'm trying to get my app working in full screen mode, and I've run into something I can't explain: two (seemingly equivalent) children of a StackLayout are getting different widths. Here's the code to reproduce it:

// Main.qml
import QtQuick
import QtQuick.Controls
import QtQuick.Layouts
ApplicationWindow {
    id: mainWindow
    visibility: Window.AutomaticVisibility
    visible: true
    flags: Qt.FramelessWindowHint | Qt.Window
    width: Screen.width
    height: Screen.height
    ColumnLayout {
        anchors.fill: parent
        spacing: 0
        Maincontent {}
    }
}

// Maincontent.qml
import QtQuick
import QtQuick.Layouts

StackLayout {
    id: mainContent
    Layout.fillHeight: true
    Layout.fillWidth: true
    SpacesScreen {
        id: spacesScreen
    }
    EquipmentScreen {
        id: equipmentScreen
    }
}

// SpacesScreen.qml
import QtQuick
import QtQuick.Controls
Pane {
    id: spacesPane
    Component.onCompleted: {
        console.log("SpacesScreen.qml: spacesPane.width is " + spacesPane.width)
    }
}

// EquipmentScreen.qml
import QtQuick
import QtQuick.Controls
Pane {
    id: equipmentPane
    Component.onCompleted: {
        console.log("EquipmentScreen.qml: equipmentPane.width is " + equipmentPane.width)
    }
}

Here's the output:

qml: EquipmentScreen.qml: equipmentPane.width is 24 // WRONG
qml: SpacesScreen.qml: spacesPane.width is 1920

I've discovered that if I add this line in my use of EquipmentScreen, I get the desired answer:

    EquipmentScreen {
        id: equipmentScreen
        implicitWidth: mainContent.width // this makes it work OK.
    }

But I don't understand why I should have to do that. Can anyone explain what's going on here? I've tried Qt 6.5.3 and 6.7.1 with the same results.

Thanks...

GrecKo

@mzimmers Is the with of equipmentPane always wrong or only in inCompleted? The StackLayout might take a couple of frames to settle on its children size.

@JoeCFD In a StackLayout, children fill the layout by default.

JoeCFD

If width or height is not specified, an item's effective size will be determined by its implicitWidth or implicitHeight. However, if an item is the child of a layout, the layout will determine the item's preferred size using its implicit size. In such a scenario, the explicit width or height will be ignored.

GrecKo

@mzimmers Is the with of equipmentPane always wrong or only in inCompleted? The StackLayout might take a couple of frames to settle on its children size.

@JoeCFD In a StackLayout, children fill the layout by default.

mzimmers

@GrecKo said in StackLayout children have unpredictable widths:

Is the with of equipmentPane always wrong or only in inCompleted?

I'm not sure...the behavior now seems to be somewhat unpredictable.

@GrecKo said in StackLayout children have unpredictable widths:

The StackLayout might take a couple of frames to settle on its children size.

Ah. So, what does one do to obviate this?