QSingleInstance

A simple single instance application for Qt

Features

• Allows to run an application as "single instance"
  • This means only one instance at a time of the application will be running
  • Subsequent starts send their arguments to the running instance, instead of starting a new one
  • Instances are generated per user
• It supports all kinds of applications, with or without gui.
  • For gui/widgets applications, you can register a window to be activated

Installation

The package is providet as qpm package, de.skycoder42.qsingleinstance. To install:

1. Install qpm (See GitHub - Installing, for windows see below)
2. In your projects root directory, run qpm install de.skycoder42.qsingleinstance
3. Include qpm to your project by adding include(vendor/vendor.pri) to your .pro file

Check their GitHub - Usage for App Developers to learn more about qpm.

Important for Windows users: QPM Version 0.10.0 (the one you can download on the website) is currently broken on windows! It's already fixed in master, but not released yet. Until a newer versions gets released, you can download the latest dev build from here:

• https://storage.googleapis.com/www.qpm.io/download/latest/windows_amd64/qpm.exe
• https://storage.googleapis.com/www.qpm.io/download/latest/windows_386/qpm.exe

Usage

Check the three example projects to see what you can do for each application type. The following shows a simple console-based example:

#include <qsingleinstance.h>

int main(int argc, char *argv[])
{
	QCoreApplication a(argc, argv);
	QSingleInstance instance;

	//this lambda only gets executed on the first instance
	instance.setStartupFunction([&]() -> int {
		qDebug() << "Instance running! Start another with -quit as first argument to exit";
		return 0;
	});

	//new instances send their arguments and this signal is received on the main instance
	QObject::connect(&instance, &QSingleInstance::instanceMessage, [&](QStringList args){
		qDebug() << "New Instance:" << args;
		if(args.size() > 1 && args[1] == "-quit")
			qApp->quit();
	});

	return instance.singleExec();
}