Qt Quick Layouts Overview

The QML types can be imported into your application using the following import statement in your .qml file.

import QtQuick.Layouts

Some of the key features are:

• Alignment of items can be specified with the Layout.alignment property

• Resizable items can be specified with the Layout.fillWidth and Layout.fillHeight properties.

• Size constraints can be specified with Layout.minimumWidth, Layout.preferredWidth, and Layout.maximumWidth properties ("Width" can be replaced with "Height" for specifying similar constraints to the height).

• Spacings can be specified with spacing, rowSpacing or columnSpacing

In addition to the above features, GridLayout adds these features:

• Grid coordinates can be specified with the Layout.row and Layout.column properties.

• Automatic grid coordinates used together with the flow, rows, and columns properties.

• Spans across rows or columns can be specified with the Layout.rowSpan and Layout.columnSpan properties.

Window {
    RowLayout {
        anchors.fill: parent
        spacing: 6
        Rectangle {
            color: 'azure'
            Layout.preferredWidth: 100
            Layout.preferredHeight: 150
        }
        Rectangle {
            color: "plum"
            Layout.fillWidth: true
            Layout.fillHeight: true
        }
    }
}

As the intention of using a layout is to rearrange its children whenever the layout changes size, the application should make sure that the layout gets resized. In the above snippet the RowLayout ensures that by specifying anchors.fill: parent. However, it can also be by other means, such as directly specifying width and height properties. In the same snippet, the azure Rectangle has a fixed size of (100, 150) pixels, and the plum Rectangle will expand to occupy all the space it gets allocated.

All items in the layout will have 6 pixels of spacing between them:

spacing: 6

Size Constraints▲

Since an item can be resized by its layout, the layout needs to know the minimum, preferred, and maximum sizes of all items where Layout.fillWidth or Layout.fillHeight is set to true.

The preferred width and height is the actual width and height of an item if the layout is not bound to a specific size itself. If the layout is set to a specific size, it will distribute additional space based on the ratio of preferred sizes of its items (taking minimum and maximum sizes into account).

For instance, the following will produce a layout with two rectangles lying side-by-side that stretches horizontally. The azure rectangle can be resized from 50x150 to 300x150, and the plum rectangle can be resized from 100x100 to ∞x100. As long as the minimum and maximum width of each item is not reached, the plum rectangle will have two times the width of the azure one.

 

Sélectionnez

RowLayout {
    id: layout
    anchors.fill: parent
    spacing: 6
    Rectangle {
        color: 'azure'
        Layout.fillWidth: true
        Layout.minimumWidth: 50
        Layout.preferredWidth: 100
        Layout.maximumWidth: 300
        Layout.minimumHeight: 150
        Text {
            anchors.centerIn: parent
            text: parent.width + 'x' + parent.height
        }
    }
    Rectangle {
        color: 'plum'
        Layout.fillWidth: true
        Layout.minimumWidth: 100
        Layout.preferredWidth: 200
        Layout.preferredHeight: 100
        Text {
            anchors.centerIn: parent
            text: parent.width + 'x' + parent.height
        }
    }
}

Combining each item's constraints will give these implicit constraints to the layout element:

	minimum	preferred	maximum
implicit constraints (width)	156	306	∞ (Number.POSITIVE_INFINITY)
implicit constraints (heights)	150	150	150

Thus, the layout cannot be narrower than 156 or be taller or shorter than 150 without breaking any of the constraints of its child items.

Specifying Preferred Size▲

You can just use normal anchoring concepts to ensure that the layout will follow the window resizing.

RowLayout {
    id: layout
    anchors.fill: parent

The size constraints of layouts can be used to ensure that the window cannot be resized beyond the layout constraints. You can take the size constraints from the layout and set these constraints on the minimumWidth, minimumHeight, maximumWidth, and maximumHeight of the Window element. The following code ensures that the window cannot be resized beyond the constraints of the layout:

minimumWidth: layout.Layout.minimumWidth
minimumHeight: layout.Layout.minimumHeight
maximumWidth: 1000
maximumHeight: layout.Layout.maximumHeight

Finally, you usually want the initial size of the window to be the layout's implicit size:

width: layout.implicitWidth
height: layout.implicitHeight