Learn Qt 5

Nicholas Sherriff (Nick)

• Publisher: Packt Publishing
• Year: 2018
• eBook ISBN: 9781788473682
• Edition: 1
• Topic: Informatik
• Subtopic: Desktop-Anwendungen

Learn the fundamentals of QT 5 framework to develop interactive cross-platform applicationsAbout This Book• A practical guide on the fundamentals of application development with QT 5• Learn to write scalable, robust and adaptable C++ code with QT• Deploy your application on different platforms such as Windows, Mac OS, and LinuxWho This Book Is ForThis book is for application developers who want a powerful and flexible framework to create modern, responsive applications on Microsoft Windows, Apple Mac OS X, and Linux desktop platforms. You should be comfortable with C++ but no prior knowledge of Qt or QML is required.What You Will Learn• Install and configure the Qt Framework and Qt Creator IDE• Create a new multi-project solution from scratch and control every aspect of it with QMake• Implement a rich user interface with QML• Learn the fundamentals of QtTest and how to integrate unit testing• Build self-aware data entities that can serialize themselves to and from JSON• Manage data persistence with SQLite and CRUD operations• Reach out to the internet and consume an RSS feed• Produce application packages for distribution to other usersIn DetailQt is a mature and powerful framework for delivering sophisticated applications across a multitude of platforms. It has a rich history in the Linux world, is widely used in embedded devices, and has made great strides in the Mobile arena over the past few years. However, in the Microsoft Windows and Apple Mac OS X worlds, the dominance of C#/.NET and Objective-C/Cocoa means that Qt is often overlooked.This book demonstrates the power and flexibility of the Qt framework for desktop application development and shows how you can write your application once and deploy it to multiple operating systems. Build a complete real-world line of business (LOB) solution from scratch, with distinct C++ library, QML user interface, and QtTest-driven unit-test projects.This is a suite of essential techniques that cover the core requirements for most LOB applications and will empower you to progress from a blank page to shipped application.Style and approachThis book takes a hands-on approach to app development that emphasizes the key concepts while you're doing the project work.

Persistence

In Chapter 5, Data, we created a framework for capturing and holding data in memory. However, this is only half of the story, as without persisting the data to some external destination, it will be lost as soon as we close the application. In this chapter, we will build on our earlier work and save our data to disk in a SQLite database so that it can live on beyond the lifetime of the application. Once saved, we will also build methods for finding, editing, and deleting our data. To get all these operations for free in our various data models, we will extend our data entities so that they can load and save to our database automatically, without us having to write boilerplate code in each class. We will cover the following topics:

• SQLite
• Primary keys
• Creating clients
• Finding clients
• Editing clients
• Deleting clients

SQLite

General purpose database technology has fragmented in the recent years with the explosion of NoSQL and Graph databases. However, SQL databases are still fighting fit and absolutely an appropriate choice in a lot of applications. Qt comes with built-in support for several SQL database driver types, and can be extended with custom drivers. MySQL and PostgreSQL are very popular open source SQL database engines and are both supported by default, but are intended for use on servers and require administration, which makes them a bit unnecessarily complicated for our purposes. Instead, we will use the much more lightweight SQLite, which is commonly used as a client-side database and is very popular in mobile applications due to its small footprint.

According to the official website at https://www.sqlite.org, "SQLite is a self-contained, high-reliability, embedded, full-featured, public-domain, SQL database engine. SQLite is the most used database engine in the world". Paired with Qt's SQL related classes, it's a snap to create a database and store your data.

The first thing we need to do is add the SQL module to our library project to get access to all of Qt’s SQL goodness. In cm-lib.pro, add the following:

QT += sql

Next, we’ll take onboard what we discussed in the previous chapter and implement our database-related functionality behind an interface. Create a new i-database-controller.h header file in cm-lib/source/controllers:

#ifndef IDATABASECONTROLLER_H #define IDATABASECONTROLLER_H #include <QJsonArray> #include <QJsonObject> #include <QList> #include <QObject> #include <QString> #include <cm-lib_global.h> namespace cm { namespace controllers { class CMLIBSHARED_EXPORT IDatabaseController : public QObject { Q_OBJECT public: IDatabaseController(QObject* parent) : QObject(parent){} virtual ~IDatabaseController(){} virtual bool createRow(const QString& tableName, const QString& id, 
 const QJsonObject& jsonObject) const = 0; virtual bool deleteRow(const QString& tableName, const QString& id) 
 const = 0; virtual QJsonArray find(const QString& tableName, const QString& 
 searchText) const = 0; virtual QJsonObject readRow(const QString& tableName, const 
 QString& id) const = 0; virtual bool updateRow(const QString& tableName, const QString& id, 
 const QJsonObject& jsonObject) const = 0; }; }} #endif

Here, we are implementing the four basic functions of (Create, Read, Update, and Delete) CRUD, which are relevant to persistent storage in general, not just SQL databases. We supplement these functions with an additional find() method that we will use to find an array of matching clients based on supplied search text.

Now, let’s create a concrete implementation of the interface. Create a new DatabaseController class in cm-lib/source/controllers.

database-controller.h:

#ifndef DATABASECONTROLLER_H #define DATABASECONTROLLER_H #include <QObject> #include <QScopedPointer> #include <controllers/i-database-controller.h> #include <cm-lib_global.h> namespace cm { namespace controllers { class CMLIBSHARED_EXPORT DatabaseController : public IDatabaseController { Q_OBJECT public: explicit DatabaseController(QObject* parent = nullptr); ~DatabaseController(); bool createRow(const QString& tableName, const QString& id, const 
 QJsonObject& jsonObject) const override; bool deleteRow(const QString& tableName, const QString& id) const 
 override; QJsonArray find(const QString& tableName, const QString& 
 searchText) const override; QJsonObject readRow(const QString& tableName, const QStrin...

Table of contents

• Title Page
• Copyright and Credits
• Packt Upsell
• Contributors
• Preface
• Hello Qt
• Project Structure
• User Interface
• Style
• Data
• Unit Testing
• Persistence
• Web Requests
• Wrapping Up
• Other Books You May Enjoy