/ models

Data Models Deconstructed - Part 1: QML / JS Arrays

Qt provides many different methods of exposing data and using data in QML Model Views, i.e. the ListView, PathView, or GridView

Over this many part series of posts, we will investigate the many methods of exposing data to QML views – starting from the simplest, to the most complex.

QML / Javascript Array

The simplest method is using a Javascript array to feed primitive type-based data into a ListView.

All QML delegates inside a model view contain a model property that represents the data for that particular index in the data model array.

In this example, the data model is a JS array – therefore, the data is available directly through the modelData property of the model object.

Qt documentation uses magic to demonstrate this. They use modelData directly since this pointer is available as a context property of the delegate. It is optional to reference the color value using model.modelData but it is more verbose to a bystander reading the code.

import QtQuick 2.5

Item {
    id: root
    
    property var colors: ["red", "white", "blue"]

    width: 640; height: 480

    ListView {
        id: _listView
        anchors.fill: parent

        model: root.colors
        delegate: Rectangle {
            id: _rectangleDelegate
            width: ListView.view.width
            height: ListView.view.height / 3
            
            // Use the colors array to change
            // the color of this Rectangle
            color: model.modelData

            // Many times developers misuse
            // model views by accessing the array
            // directly, i.e.
            // color: root.colors[model.index]
            // or
            // color: root.colors[index]
        }
    }
}

Niraj Desai

Niraj Desai

UI enthusiast, Qt / QML loyalist, passion for automotive UX – previously at Mercedes-Benz R&D, currently at NIO US.

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