Integrate a Qt static library with running QCoreApplication into an android app over JNI

moozoom

I need help for an integration project.

I developed a static library in Qt with async tasks or event loops like QCoreApplication and QNetworkAccessManager. In my static library I need a QCoreApplication instance and a QNetworkAccessManager instance. Principally the library includes signal-slots-mechanism.

In a past integration project I integrated this library into a native objC iOS app - this solution works fine.

Now, I will integrate this library into a native JAVA Android app over JNI - this step is very tricky for me.

First, I have an simple Qt class:

#ifndef TEST_H
#define TEST_H
#include <QObject>
#include <QNetworkAccessManager>
class Test : public QObject
{
public:
    explicit Test(QObject *parent = 0);
    void initManager();
private:
    QNetworkAccessManager *manager;
};
#endif // TEST_H

This Test.class create a simple instance for QNetworkAccessManager and QCoreApplication:

#include "Test.h"

#include <QDebug>
#include <QCoreApplication>

Test::Test(QObject *parent):
    QObject(parent)
{
}

void Test::initManager()
{
	qDebug() << "# initManager #";
	
	this->onStarted(); // Direct function call; runs onStarted() in the main thread. - or not?

	// Create a manager instance
    qDebug() << "NEW QNetworkAccessManager instance ...";

    manager = new QNetworkAccessManager(this);

    qDebug() << "QNetworkAccessManager instantiated ...";

    QCoreApplication::exec();
}

void Test::onStarted()
{
	qDebug() << "# onStarted #";

	if (QCoreApplication::instance() == NULL)
	{
		qDebug() << "NEW QCoreApplication instance ...";

		int argc = 1;
		char * argv[] = {"webdav.app", NULL};

		new QCoreApplication(argc, argv);

		qDebug() << "QCoreApplication instantiated ...";
	}

	return;
}

Now I call the method initManager() in my native android app over JNI:

static MYQLibrary webDAV;

extern "C" {
	JNIEXPORT void JNICALL Java_com_dictateam_MYQLibrary_Interface_initManager(JNIEnv * env, jobject obj);
};

JNIEXPORT void JNICALL Java_com_dictateam_MYQLibrary_Interface_initManager(JNIEnv * env, jobject obj)
{
	webDAV.initManager();

	return;
}

In JAVA (native Android in MainActivity.onCreate()) I call the native method:

final Interface myInterface = new Interface();

System.out.println("Call initManager() from lib:");

Runnable r = new Runnable() {
	public void run() {
		try{
			myInterface.initManager();
		}catch(Exception e){
			System.out.println(e.toString());
		}
	}
};
new Thread(r).start();

If i run this application on my smartphone, the app crashes with following log:

05-25 12:50:29.936: I/System.out(6341): Call debug() from lib:
05-25 12:50:29.936: D/(6341): ../MYQLibrary/MYQLibrary.cpp:93 (void MYQLibrary::debug() const): The MYQLibrary() says hello!
05-25 12:50:29.936: I/System.out(6341): Call initManager() from lib:
05-25 12:50:29.941: D/(6341): ../MYQLibrary/MYQLibrary.cpp:98 (void MYQLibrary::initManager()): # initManager #
05-25 12:50:29.941: W/(6341): (null):0 ((null)): QObject: Cannot create children for a parent that is in a different thread.
05-25 12:50:29.941: W/(6341): (Parent is MYQLibrary(0x60f83098), parent's thread is QThread(0x5cedfed0), current thread is QThread(0x5c8dac58)
05-25 12:50:29.941: D/(6341): ../MYQLibrary/test.cpp:14 (void Test::initManager()): # initManager #
05-25 12:50:29.941: D/(6341): ../MYQLibrary/test.cpp:75 (void Test::onStarted()): # onStarted #
05-25 12:50:29.941: D/(6341): ../MYQLibrary/test.cpp:83 (void Test::onStarted()): NEW QCoreApplication instance ...
05-25 12:50:29.941: W/(6341): (null):0 ((null)): WARNING: QApplication was not created in the main() thread.
05-25 12:50:29.941: D/webdav.app(6341): ../MYQLibrary/test.cpp:20 (void Test::initManager()): QCoreApplication::instance() is running ...
05-25 12:50:29.941: D/webdav.app(6341): ../MYQLibrary/test.cpp:23 (void Test::initManager()): NEW QNetworkAccessManager instance ...
05-25 12:50:29.941: A/libc(6341): Fatal signal 6 (SIGABRT) at 0x000018c5 (code=-6), thread 6366 (Thread-6412)
05-25 12:50:29.976: D/libEGL(6341): loaded /system/lib/egl/libEGL_mali.so
05-25 12:50:29.981: D/libEGL(6341): loaded /system/lib/egl/libGLESv1_CM_mali.so
05-25 12:50:29.981: D/libEGL(6341): loaded /system/lib/egl/libGLESv2_mali.so

How can I integrate my static library with a working event loop in the background (QCoreApplication and QNetworkAccessManager)?
This library includes several async tasks (Network communication by QNetworkAccessManager) by Signal-Slot-Mechanism. So I must have a working event loop by QCoreApplication.

Please help me to find a solution for this case. Thank you in advanced! :-)

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