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Felgo Apps Documentation

Felgo Apps is a QML module for developing feature-rich, cross-platform apps with the native look and feel of the underlying platform. It is part of the Felgo SDK. Felgo Apps components can be used to build cross-platform applications for Mobile, Desktop, Embedded and Web platforms.

QML Introduction for App Development

QML stands for "Qt Markup Language" and is a declarative language designed to describe the user interface of a program: both what it looks like, and how it behaves. In QML, a user interface is specified as a tree of objects with properties. This tree is also often referred to as Scene Graph, because when the parent item moves all children will follow. JavaScript is used as a scripting language in QML. In this section we will cover the basics of QML and its advantages by an example. In addition QML components can be linked with C++ code, allowing you to implement more complex functionality and access third-party framework integrations.

As code speaks more than 1000 words, here is a QML example implementing the following:

  • A basic app with a navigation bar holding a title and column with controls.
  • A button that can be clicked to increase a counter.
  • The button also shows the current counter value.
  • A slider that can be dragged.
  • A colored area that changes its height based on the slider value.
  • Looks native on iOS and Android.

How many lines of code would it take you to develop this application with the same functionality in another programming language? With QML, it is just about 30 lines of code:

 import Felgo
 import QtQuick

 App {
   id: app

   property int clickCount: 0 // a property of type integer, to count our button clicks

   NavigationStack { // the NavigationStack displays the navigation bar and lets you push and pop pages

     AppPage {
       title: "QML Introduction" // the title of the active page is displayed in the navigation bar

       Rectangle {
         color: "#e0e2eb"
         width: parent.width // make this rectangle the same width as its parent, which is the page
         height: parent.height * slider.value // this property binding is automatically updated when the slider value changes

       Column {
         anchors.centerIn: parent // center the column in its parent, which is the page

         AppButton {
           id: button
           text: "Click Me! " + app.clickCount // this property binding is automatically updated when the click count changes
           flat: false
           anchors.horizontalCenter: parent.horizontalCenter
           onClicked: {
             app.clickCount++ // increase the click count by 1 on every button click

         AppSlider {
           id: slider
           value: 0.2
       } //Column
     } //Page
   } //NavigationStack
 } //App

Felgo Apps makes it possible to write cross-platform apps that:

  • save time implementing cross-platforms apps from a single code base on a single development platform
  • provide a default native look & feel, so that they fit in with the visual style and user experience of the underlying mobile platform
  • add easily implemented, powerful animations thanks to Qt Quick
  • are fully customizable through a global Theme component which can be used to change colors, fonts and other attributes from a single point in code
  • make use of platform-specific features when integrating custom C++ code (or platform-specific code like Objective-C on iOS or Java on Android)

Felgo Apps Topic Overview

API Documentation

Felgo Apps includes components for developing cross-platform apps with a native look and feel to interfaces and user experience patterns.

In addition to Felgo Apps you most probably will also make use of components from the Qt Quick module provided by the Qt framework.

The current release of Felgo Apps is based on Qt 6 and QtQuick 2.

Writing Applications with Felgo Apps

QML and Qt Quick Documentation

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