Integrate C++ and QML. Qt 5.4 - c++

Question

I was reading the Qt documentation for the past couple of hours trying to figure out a way to make a UI created with Qt Quick UI (QML) communicate (interact) with C++ code (functions... etc.).
I've read the 5 or 6 similar questions on here to but I'm kind of confused, I have problems figuring out where to start or what to do first.
I'd appreciate it a lot if someone could take the time and list the steps needed to make this work.
What i've done so far. I tried doing ...>add new Item> C++ class but I failed with an error saying:" failed to add one or more files to project"> It seems like the files (.. .cpp and .h) are created, they were in the folder where the other project files were but not included in the project.
What I wanna do is just something simple like changing the text of the textedit through a C++ function or any other way possible.
//Test.qml (main.qml)
import QtQuick 2.1
import QtQuick.Window 2.0
Rectangle {
id: rootRect
width: Screen.width/2
height: Screen.height/2
color: "gray"
Button{}
Rectangle{
id: textField
width: 120
height: 40
color: "white"
x:274; y: 61
border.color: "blue"
border.width: 4
radius: 2
}
TextEdit {
id: display
x: 274
y: 61
width: 80
height: 20
text: qsTr("Text Edit")
font.pixelSize: 22
color: "black"
anchors.centerIn: textField
}
Rectangle{
id: inputField
width: textField.width
height: textField.height
border.color: "green"
border.width: 3
color: "white"
x: 140; y: 61
}
TextEdit{
id: input
color: "red"
font.pixelSize: 30
anchors.centerIn: inputField
text: "Some Text"
}
}
//Button.cpl
import QtQuick 2.0
import QtQuick.Window 2.0
Item {
property string defaultText: "New Text"
Rectangle{
id: button
width: rootRect.width/6
height: rootRect.height/8
color: "black"
x: 200; y: 200
radius: 10
}
MouseArea{
id: buttonClickArea
width: 0
anchors.rightMargin: 0
anchors.bottomMargin: 0
anchors.fill: button
onClicked: {
display.text = defaultText
}
}
}
Thank you for taking the time to read this and/or any replies.

Answer 1

Using Qt 5.4.0 and Qt Creator 3.3.0, create New Project:
Click New Project
Qt Quick Application
Click Choose...
Name the project and select where to place it
Click Next
Select Qt Quick 2.4 from the drop-down menu
Click Next
Select desired Kit(s)
Click Next
Click Finish
Now You should see open main.qml file with following code:
import QtQuick 2.4
import QtQuick.Window 2.2
Window {
visible: true
MainForm {
anchors.fill: parent
mouseArea.onClicked: {
Qt.quit();
}
}
}
Change it to:
import QtQuick 2.4
import QtQuick.Window 2.2
//### New Code ###
import QtQuick.Controls 1.3
//################
Window {
id: window1
visible: true
//### New Code ###
width: 400
height: 500
TextArea {
id: textArea
readOnly: true
anchors.bottom: textInput.top
anchors.bottomMargin: 6
anchors.right: parent.right
anchors.rightMargin: 8
anchors.left: parent.left
anchors.leftMargin: 7
anchors.top: parent.top
anchors.topMargin: 7
}
TextField {
id: textInput
y: 470
height: 23
anchors.right: sendButton.left
anchors.rightMargin: 6
anchors.bottom: parent.bottom
anchors.bottomMargin: 7
anchors.left: parent.left
anchors.leftMargin: 7
}
Button {
id: sendButton
x: 328
y: 470
width: 64
height: 23
text: qsTr("Send")
anchors.bottom: parent.bottom
anchors.bottomMargin: 7
anchors.right: parent.right
anchors.rightMargin: 8
onClicked: {
CppClass.sendMessage(textInput.text, textArea);
textInput.text = "";
}
}
//################
}
Add C++ Class to Your project:
Right Mouse Click project name in Projects viewer
Click Add New...
Select C++ Class if not already selected
Click Choose...
In Class name filed enter "CppClass"
Set Base class to QObject
Click Next
Click Finish
Open cppclass.h and change it to:
#ifndef CPPCLASS_H
#define CPPCLASS_H
#include <QObject>
//### New Code ###
#include <QQuickItem>
#include <QQuickTextDocument>
#include <QTextDocument>
//################
class CppClass : public QObject
{
Q_OBJECT
public:
explicit CppClass(QObject *parent = 0);
~CppClass();
//### New Code ###
Q_INVOKABLE void sendMessage(const QString &msg, QQuickItem *textArea);
//################
signals:
public slots:
};
#endif // CPPCLASS_H
Open cppclass.cpp and change it to:
#include "cppclass.h"
CppClass::CppClass(QObject *parent) : QObject(parent)
{
}
CppClass::~CppClass()
{
}
//### New Code ###
void CppClass::sendMessage(const QString &msg, QQuickItem *textArea)
{
QTextDocument *textDocument = textArea->property("textDocument").value<QQuickTextDocument*>()->textDocument();
textDocument->setHtml(textDocument->toHtml() + "\n<b>Text sent to Cpp side:</b> <i>" + msg + "</i>");
}
//################
Open main.cpp and change it to:
#include <QGuiApplication>
#include <QQmlApplicationEngine>
//### New Code ###
#include <QQmlContext>
#include "cppclass.h"
//################
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
//### New Code ###
CppClass cppClass;
engine.rootContext()->setContextProperty("CppClass", &cppClass);
//################
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
Run Your application, type some text to Input Field and click send.
In response to Dynamic Remo comment here's another way to have QML and C++ communicate. This approach is based on C++ emitting a signal and QML acting upon it. Following is the code to get it working.
cppclass.h
#ifndef CPPCLASS_H
#define CPPCLASS_H
#include <QObject>
#include <QDateTime>
class CppClass : public QObject
{
Q_OBJECT
public:
explicit CppClass(QObject *parent = 0);
~CppClass();
Q_INVOKABLE void getCurrentTime();
signals:
void timeUpdate(QString currentTime);
public slots:
};
#endif // CPPCLASS_H
cppclass.cpp
#include "cppclass.h"
CppClass::CppClass(QObject *parent) : QObject(parent)
{
}
CppClass::~CppClass()
{
}
void CppClass::getCurrentTime()
{
emit timeUpdate(QDateTime::currentDateTime().toString("ddd dd MMMM yyyy hh:mm:ss.zzz"));
}
main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "cppclass.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
CppClass cppClass;
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("CppClass", &cppClass);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
return app.exec();
}
main.qml:
import QtQuick 2.4
import QtQuick.Window 2.2
import QtQuick.Controls 1.2
Window {
id: rootWindow
width: 400
height: 400
visible: true
Connections {
target: CppClass
onTimeUpdate: {
initailizeDllMsg.text = currentTime
}
}
Text {
id: initailizeDllMsg
text: qsTr("{current time placeholder}")
font.pointSize: 14
anchors.horizontalCenter: parent.horizontalCenter
anchors.verticalCenter: parent.verticalCenter
}
Button {
id: button1
x: 163
y: 357
text: qsTr("Show current time")
anchors.bottom: parent.bottom
anchors.bottomMargin: 20
anchors.horizontalCenter: parent.horizontalCenter
onClicked: CppClass.getCurrentTime()
}
}