My custom C++ plugin is not being consumed by the qml test application

Question

I am new to Qt and learning few of the modules in Qt-Qml from youtube and Qt documentation. I want to create cpp plugin which is to be consumed by the qml application.

For this, I have created two projects. One is for creating a plugin library and another application is for consuming the plugin.

I am able to create the plugin library successfully. But, not able to consume it by the test application.

The test application is compiled successfully but throwing below error during run time.

QQmlApplicationEngine failed to load component qrc:/main.qml:3:1: module "MyPlugin" is not installed

I have read the Qt documentation and googled a lot, but could not able to resolve it.

• Qt : 5.15.7
• Qt Creator: 5.0.3
• OS: Ubuntu 18.04

Project 1: Creating Plugin library

CreatePlugin.pro

TEMPLATE = lib
TARGET = CreatePlugin
QT += qml quick
CONFIG += plugin c++11

DESTDIR = ../pluginFiles
TARGET = $$qtLibraryTarget($$TARGET)
uri = MyPlugin

# Input
SOURCES += \
createplugin_plugin.cpp \
myplugin.cpp

HEADERS += \
createplugin_plugin.h \
myplugin.h

DISTFILES = qmldir

!equals(_PRO_FILE_PWD_, $$OUT_PWD) {
    copy_qmldir.target = $$OUT_PWD/qmldir
    copy_qmldir.depends = $$_PRO_FILE_PWD_/qmldir
    copy_qmldir.commands = $(COPY_FILE) "$$replace(copy_qmldir.depends, /, $$QMAKE_DIR_SEP)" 
"$$replace(copy_qmldir.target, /, $$QMAKE_DIR_SEP)"
   QMAKE_EXTRA_TARGETS += copy_qmldir
   PRE_TARGETDEPS += $$copy_qmldir.target
}

qmldir.files = qmldir
unix {
    installPath = $$[QT_INSTALL_QML]/$$replace(uri, \., /)
    qmldir.path = $$installPath
    target.path = $$installPath
    INSTALLS += target qmldir
}

# Copy the qmldir file to the same folder as the plugin binary
cpqmldir.files = qmldir
cpqmldir.path = $$DESTDIR
COPIES += cpqmldir

createplugin_plugin.h

#ifndef CREATEPLUGIN_PLUGIN_H
#define CREATEPLUGIN_PLUGIN_H

#include <QQmlExtensionPlugin>

class CreatePluginPlugin : public QQmlExtensionPlugin
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)

public:
    void registerTypes(const char *uri) override;
};

#endif // CREATEPLUGIN_PLUGIN_H

createplugin_plugin.cpp

#include "createplugin_plugin.h"

#include "myplugin.h"

#include <qqml.h>

void CreatePluginPlugin::registerTypes(const char *uri)
{
    // @uri MyPlugin
    qmlRegisterType<MyPlugin>(uri, 1, 0, "MyPlugin");
}

myplugin.h

#ifndef MYPLUGIN_H
#define MYPLUGIN_H

#include <QObject>
#include <QString>

class MyPlugin : public QObject
{
    Q_OBJECT
    Q_DISABLE_COPY(MyPlugin)

public:
    explicit MyPlugin(QObject *parent = nullptr);
    ~MyPlugin() override;

public slots:
    QString getString();
};
#endif // MYPLUGIN_H

myplugin.cpp

#include "myplugin.h"

MyPlugin::MyPlugin(QObject *parent)
    : QObject(parent)
{
    // By default, QQuickItem does not draw anything. If you subclass
    // QQuickItem to create a visual item, you will need to uncomment the
    // following line and re-implement updatePaintNode()

    // setFlag(ItemHasContents, true);
}

MyPlugin::~MyPlugin()
{
}

QString MyPlugin::getString()
{
    return "This is CPP String";
}

qmldir

module MyPlugin
plugin CreatePlugin

Project 2: TestPlugin

TestPlugin.pro

QT += quick

CONFIG += c++11

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before 
Qt 6.0.0

SOURCES += \
        main.cpp

RESOURCES += qml.qrc

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>


int main(int argc, char *argv[])
{
    #if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    #endif

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                 &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

main.qml

import QtQuick 2.12
import QtQuick.Window 2.12
import MyPlugin 1.0 

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    MyPlugin {
        id: mypluginId
    }

    Component.onCompleted: console.log(mypluginId.getString())
}