Call own non static java method from QT/C++

Question

I am trying to call non static method callNative of my own Java class from QT/C++ but I get the following error:

W System.err: java.lang.NoSuchMethodError: no non-static method "Lorg/qtproject/qt5/android/bindings/QtActivity;.callNative()V;"

Here is the code of java class:

package com.ieio.finger;


import static java.lang.System.out;

public class Finger extends org.qtproject.qt5.android.bindings.QtActivity {
    public void callNative()
        {
            System.out.println("I am in Java");
        }
}

Here the C++ code finger.h

#ifndef FINGER_H
#define FINGER_H

#include <QObject>

class finger : public QObject
{
    Q_OBJECT
public:
    explicit finger(QObject *parent = nullptr);
    Q_INVOKABLE void call_java();
signals:

public slots:
};

#endif // FINGER_H

finger.cpp:

#include <QtAndroidExtras/QAndroidJniObject>
#include <QtAndroidExtras/QtAndroid>
#include "finger.h"


finger::finger(QObject *parent) : QObject(parent)
{

}

void finger::call_java()
{
    qDebug()<< "call java";
    QtAndroid::androidActivity().callObjectMethod("callNative","()V;");
    qDebug()<< "called java";
}

main.cpp:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

#include <finger.h>

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

        QQmlApplicationEngine engine;
        qmlRegisterType<finger>("io.qt.ieio.finger", 1, 0, "Finger");

        engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
        if (engine.rootObjects().isEmpty())
            return -1;

        return app.exec();
    }

and the qml:

import QtQuick 2.9
import QtQuick.Window 2.2
import QtQuick.Controls 2.2

import io.qt.ieio.finger 1.0

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


    Finger
    {
        id:myFinger
    }

    Button {
        id: button
        x: 234
        y: 284
        text: qsTr("Button")
        onClicked: {
            myFinger.call_java()
        }
    }
}

Any ideas why I get java.lang.NoSuchMethodError ?

Answer 1

Eventually I found a solution: I changed the method:

void finger::call_java()
{
    qDebug()<< "call java";
    QtAndroid::androidActivity().callObjectMethod("callNative","()V;");
    qDebug()<< "called java";
}

in

void finger::call_java()
{
    qDebug()<< "call java";
    QtAndroid::runOnAndroidThread([]{
        QAndroidJniObject myJavaObject("com/ieio/finger/Finger");
        myJavaObject.callMethod<void>("callNative","()V");
    });
    qDebug()<< "called java";
}