Qt Multiplatform development

start

Qt for beginners

Multiplatform development

with QtFramework

Sergiy Shevchenko

eTuitus S.r.l 2016

Part 2

Table of

Contents

01 Qml/C++ communicationBasic signal/slot concepts of qml/c++ communication

02 Qt for mobileCross-platform mobile development

03 Connecting C++ to nativeHow to interface with native Java and Objective C environments

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QML/Qt communication

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• Gui creates an event (click on button)• QML (via JS) invokes business logic in Qt• Business logic does something and returns a

result

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QML/Qt communicationPrepare object to expose (from C++ to QML)

//AbstractVibrator.h#include <QObject>

class AbstractVibrator : public QObject{ Q_OBJECTpublic: explicit AbstractVibrator(QObject *parent = 0);

Q_INVOKABLE virtual bool vibrate() = 0;};

Extends QObject

Q_INVOKABLE macro

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QML/Qt communicationExpose AbstractVibrator to QML

//main.cpp#include <QQmlApplicationEngine>#include <QQmlContext>

int main(int argc, char *argv[]){

QGuiApplication app(argc, argv);QQmlApplicationEngine engine;

qmlRegisterType<AbstractVibrator>();engine.rootContext()->setContextProperty("facadeVibrator", NativeAbstraction::getVibrateImpl());

engine.load(QUrl(QStringLiteral("qrc:/main.qml")));return app.exec();

}

Include DOM manipulation headers

Register new QML type

Set name and pass a pointer

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QML/Qt communicationAccess to facade from QML

Window { //...

MainForm { //...

vibrate.onClicked: { if(facadeVibrator.vibrate()){

console.log("Vibrate success");}else{

console.log("Vibration failed");}

}}

Just invoke function by name

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QML/Qt communicationDatatypes

JavaScript (QML) is dynamic, untyped, and interpreted programming language. On other side C++ is compiled and statically typed language.How do they deal together?

• QVariant (QString, int ecc..)• Registering type with qRegisterMetaType

and qmlRegisterType

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QML/Qt communicationDatatypes - pointers

Do not use pointers to C++ objects in QML!

If you have to, make a copy of object and return a pointer to a copy

Why? JavaScript has a GC so it will deallocate pointed object at most inconvenient time

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QML/Qt communicationDatatypes - pointers

SigningLibrary.cpp

SigningFacade.cpp

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QML/Qt communicationSync/Async

Invoking C++ code from QML means that C++ will be executed in the same thread (GUI)

Solution use Facade pattern

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QML/Qt communicationFacade design pattern

QML

C++

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QML/Qt communicationAsync facade

Event starts here

Create new Thread and invoke getPrime

Invoke C++obtain a return

Once result is ready emit signal

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QML/Qt communicationAsync Facade

MainForm.ui.qml

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QML/Qt communicationAsync Facade MainForm.qml

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QML/Qt communicationAsync Facade

main.cpp

PrimeFacade.h PrimeFacade.cpp

PrimeGenerator.h

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LIVE

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Cross-platform mobile development

Integration with native APIs

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What do we need?

•Qt >= 5.5•Android SDK Tools e Android Studio•Android NDK•JDK v7 or major•XCode 7

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Generic application

Packaging• .APK• Gradle or ANT• .IPA• XCode export

tool

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QtCreator config

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Simple projectOnce pressed "Vibrate" button device must

vibrate using integrated vibrator

Problem?Each platform realises vibration API differently and in native code!

QT -> NATIVE

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Things to do

• Lets create an empty project or use existing one (will be provided)

• Make gui with simple call to facade• Create platform independent

abstraction for vibration service• Write function calling Android

Vibration API in java• Write function calling iOS

Vibration API in Objective C• Implement bridges and trampoline

for Android and iOS respectively• Be happy!

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Project setup

• Modular structure• /platform/ contains all

native code• android project can be

opened with Android Studio• Once compiled iOS project

can be edited in XCode

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Vibration abstractions

<<use>>

<<use>>

<<use>>

<<use>>

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JNI

The Java Native Interface (JNI) is a programming framework that enables Java code running in a Java Virtual Machine (JVM) to call and be called by native applications or libraries written in other languages such as C, C++ and assembly.

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Vibration abstractions

AbstractVibrator.h

AndroidVibrator.hSpecificimplementation

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Android Native Impl.

AndroidVibrator.cpp

EtMobileActivity.java

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IOS Native implementation

VibratorTrampoline.h

IOSVibrator.cpp

VibratorTrampoline.mm

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Orchestrating classesNativeAbstraction.cpp

NativeAbstraction.h

main.cpp

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Orchestrating filescore.pro

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Handling device events

• For iOS things are simple: just include l• Android needs JNI exported functions

NATIVE -> QT

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Simple case: iOS

AppDelegate.mm

just include *.h

use Qt/C++ code

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Complex case: Android

•Export C functions using JNIEXPORT•Create "bridge" class with native methods in Java•Ensure Qt is running and invoke methods

Things to do

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Complex case: AndroidExport C functions

src/it/infocert/mobile/dike/JNIOpener.java

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Complex case: AndroidThread lifecycle

1.Call a Java method from C/C++ Qt thread. The Java method will be executed in Qt thread, so we we need a way to access Android APIs in Android UI thread.

2.Java method uses Activity.runOnUiThread to post a runnable on Android UI thread. This runnable will be executed by the Android event loop on Android UI thread.

3.The runnable accesses the Android APIs from Android UI thread.4.Call a C/C++ function from Android UI thread.5.Using QMetaObject::invokeMethod to post a method call on Qt event loop.6.Qt event loop will execute that function on Qt thread.

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Complex case: AndroidThread lifecycle

NO

main()

Start App

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Complex case: AndroidJava -> QT

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Complex case: AndroidJava -> QT

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Complex case: AndroidCheck Qt Startup

Start App

Complex case: AndroidCheck Qt Startup

QtStartMonitor.h

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Complex case: AndroidCheck Qt Startup NativeBridge.java

AndroidBridge.cpp

main.cpp

Somewhere in java...

close

Thank You

Presenter: Sergiy Shevchenko

eTuitus S.r.l 2016

Qt Multiplatform development

Technology