# SingleApplication This is a replacement of the QtSingleApplication for `Qt5` and `Qt6`. Keeps the Primary Instance of your Application and kills each subsequent instances. It can (if enabled) spawn secondary (non-related to the primary) instances and can send data to the primary instance from secondary instances. ## Documentation You can find the full usage reference [here](https://itay-grudev.github.io/SingleApplication/classSingleApplication.html). ## Usage The `SingleApplication` class inherits from whatever `Q[Core|Gui]Application` class you specify via the `QAPPLICATION_CLASS` macro (`QCoreApplication` is the default). Further usage is similar to the use of the `Q[Core|Gui]Application` classes. You can use the library as if you use any other `QCoreApplication` derived class: ```cpp #include <QApplication> #include <SingleApplication.h> int main( int argc, char* argv[] ) { SingleApplication app( argc, argv ); return app.exec(); } ``` To include the library files I would recommend that you add it as a git submodule to your project. Here is how: ```bash git submodule add https://gitee.com/tongynj/singleapplication-pri.git singleapplication ``` **Qmake:** Then include the `singleapplication.pri` file in your `.pro` project file. ```qmake include(singleapplication/singleapplication.pri) DEFINES += QAPPLICATION_CLASS=QApplication ``` **CMake:** Then include the subdirectory in your `CMakeLists.txt` project file. ```cmake set(QAPPLICATION_CLASS QApplication CACHE STRING "Inheritance class for SingleApplication") add_subdirectory(src/third-party/singleapplication) target_link_libraries(${PROJECT_NAME} SingleApplication::SingleApplication) ``` The library sets up a `QLocalServer` and a `QSharedMemory` block. The first instance of your Application is your Primary Instance. It would check if the shared memory block exists and if not it will start a `QLocalServer` and listen for connections. Each subsequent instance of your application would check if the shared memory block exists and if it does, it will connect to the QLocalServer to notify the primary instance that a new instance had been started, after which it would terminate with status code `0`. In the Primary Instance `SingleApplication` would emit the `instanceStarted()` signal upon detecting that a new instance had been started. The library uses `stdlib` to terminate the program with the `exit()` function. Also don't forget to specify which `QCoreApplication` class your app is using if it is not `QCoreApplication` as in examples above. ## Instance started signal The `SingleApplication` class implements a `instanceStarted()` signal. You can bind to that signal to raise your application's window when a new instance had been started, for example. ```cpp // window is a QWindow instance QObject::connect( &app, &SingleApplication::instanceStarted, &window, &QWindow::raise ); ``` Using `SingleApplication::instance()` is a neat way to get the `SingleApplication` instance for binding to it's signals anywhere in your program. _Note:_ On Windows the ability to bring the application windows to the foreground is restricted. See [Windows specific implementations](Windows.md) for a workaround and an example implementation. ## Secondary Instances If you want to be able to launch additional Secondary Instances (not related to your Primary Instance) you have to enable that with the third parameter of the `SingleApplication` constructor. The default is `false` meaning no Secondary Instances. Here is an example of how you would start a Secondary Instance send a message with the command line arguments to the primary instance and then shut down. ```cpp int main(int argc, char *argv[]) { SingleApplication app( argc, argv, true ); if( app.isSecondary() ) { app.sendMessage( app.arguments().join(' ')).toUtf8() ); app.exit( 0 ); } return app.exec(); } ``` _Note:_ A secondary instance won't cause the emission of the `instanceStarted()` signal by default. See `SingleApplication::Mode` for more details.* You can check whether your instance is a primary or secondary with the following methods: ```cpp app.isPrimary(); // or app.isSecondary(); ``` _Note:_ If your Primary Instance is terminated a newly launched instance will replace the Primary one even if the Secondary flag has been set.* ## Examples There are three examples provided in this repository: * Basic example that prevents a secondary instance from starting [`examples/basic`](https://github.com/itay-grudev/SingleApplication/tree/master/examples/basic) * An example of a graphical application raising it's parent window [`examples/calculator`](https://github.com/itay-grudev/SingleApplication/tree/master/examples/calculator) * A console application sending the primary instance it's command line parameters [`examples/sending_arguments`](https://github.com/itay-grudev/SingleApplication/tree/master/examples/sending_arguments) ## Versioning Each major version introduces either very significant changes or is not backwards compatible with the previous version. Minor versions only add additional features, bug fixes or performance improvements and are backwards compatible with the previous release. See [CHANGELOG.md](CHANGELOG.md) for more details. ## Implementation The library is implemented with a `QSharedMemory` block which is thread safe and guarantees a race condition will not occur. It also uses a `QLocalSocket` to notify the main process that a new instance had been spawned and thus invoke the `instanceStarted()` signal and for messaging the primary instance. Additionally the library can recover from being forcefully killed on *nix systems and will reset the memory block given that there are no other instances running. ## License This library and it's supporting documentation, with the exception of the Qt calculator examples which is distributed under the BSD license, are released under the terms of `The MIT License (MIT)` with an extra condition, that: ```txt Permission is not granted to use this software or any of the associated files as sample data for the purposes of building machine learning models. ```