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App Architecture for REST Services with Qt, QML and V-Play

REST and RESTful web services are the most common way to access data through the Internet. Qt with V-Play provides an easy way to connect via REST. This article guides you through the most important steps to create an App and connect to a REST service. Additionally, it provides reusable code snippets.

Spoiler: Basic REST Example with V-Play

Before we jump into the details of creating the sample App, this is how a basic request to a REST service looks, using the XMLHttpRequest:

// Create the XMLHttpRequest object
var xhr = new XMLHttpRequest

// Listen to the readyStateChanged signal
xhr.onreadystatechange = function() {
  // If the state changed to DONE, we can parse the response
  if (xhr.readyState === XMLHttpRequest.DONE) {
    // The responseText looks like this {"ip":"xxx.xxx.xxx.xxx"} 
    // Parse the responseText string to JSON format
    var responseJSON = JSON.parse(xhr.responseText)
    // Read the ip property of the response
    var ip = responseJSON.ip
    // Log your ip to the console output
    console.debug("My IP is: " + ip)
  }
}

// Define the target of your request
xhr.open("GET", "https://api.ipify.org?format=json")
// Execute the request
xhr.send()

Real-Life Sample Project

For the most useful results, we build a real-life Qt client. It accesses one of the web’s most popular weather services. It’s easy to adapt to any other REST service: the process is always the same. You only need to change the endpoint URL and parse the corresponding content.

The full sample is available open-source on GitHub:

Architecture

The app consists of two files:

  • Main.qml: contains the UI and REST logic
  • DataModel.qml: stores & caches the parsed data from the REST service

Basic UI for a Responsive REST Client App

First, we create the user interface: the QML items in “Main.qml”. We use V-Play APIs. They adapt to the style of the target platform (Desktop, Android, iOS). These three items are usually present in every Qt / QML app:

  1. The App component is always the top-level element in the QML file. It adds a lot of vital layout data to standard Qt classes. Two mechanisms are especially important. Device-independent pixels (dp) for sizes and scale-independent pixels (sp) for fonts.
  2. Initially, our REST client app only has a single page. It’s still a good idea to add the NavigationStack item as a child. Later, it could handle navigating to a detail page. In …read more

    Source:: https://v-play.net/cross-platform-app-development/access-rest-services-qt-v-play-weather-service-example-app-open-source

          

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