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plugin-loader.md

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Plugin Loader

CkLoader is a static library helping to do essential initializations of the plugin framework and load all plugins.

You should be well informed the plugin life cycle at Qt Creator Documentation.

About Loader

To find and load plugins is a dull and boring implementation job, we provide the common loader implementations with some hooks so that you can do some custom work while loading the plugins.

Loader Tasks

  1. Parse command line arguments
  2. Initialize ExtensionSystem::PluginManager
  3. Create a QSplashScreen and show messages
  4. Find plugins
  5. Create a SingleApplication guard
  6. Load and initialize the plugins
  7. Enter main event loop

Loader Configuration

You need to initialize the member variables in constructor.

  • allowRoot: Add an --allow-root option to the application, if the application is launched as Root/Administrator without setting this option, the loader will display a warning and exit

  • coreName: The core plugin name, the default value is Core, it's recommended that you leave it unchanged

  • pluginIID: Plugin interface ID, only Qt Plugins with this IID will be recognized as the application plugin

  • pluginPaths: Default plugin searching paths

  • splashSettingPath: The splash screen configuration path

  • extraArguments: Extra arguments that need to be shown in help text

  • userSettingsPath: QSettings directory of ExtensionSystem::PluginManager (User Scope)

  • systemSettingsPath: QSettings directory of ExtensionSystem::PluginManager (System Scope)

You may need to override the virtual functions that will be called during the plugin loading process.

  • bool preprocessArguments(QStringList &arguments, int *code)

    • You should parse your custom arguments and may do some initializations before the loader creates ExtensionSystem::PluginManager instance
    • Params
      • arguments: The remaining arguments, you should remove the ones you specified in extraArguments
      • code: The return code if parse failed

  • void beforeLoadPlugins(QSplashScreen *screen)

    • Do something before loading plugins, you can store the splash screen handle and give it to the plugins

  • void afterLoadPlugins()

    • Do something before entering the main event loop

Call LoaderConfiguration::run() to transfer control flow, make sure the QApplication and QMAppExtension instances are created before calling it

Example

The executable usually does nothing but loading the plugins, you should link CKLoader to it.

#include <QApplication>

#include <QMCoreAppExtension.h>

#include <loaderconfig.h>

class MyLoaderConfiguration : public LoaderConfiguration {
public:
    MyLoaderConfiguration() {
        QString appDir = QApplication::applicationDirPath();

        pluginIID = "org.MyOrginization.MyApplication.Plugin";
        splashSettingPath = appDir + "/config.json";
        userSettingsPath = appDir + "/settings";
        systemSettingsPath = appDir + "/settings";
        pluginPaths << (appDir + "/plugins");
    }

    bool preprocessArguments(QStringList &arguments, int *code) override {
        qDebug() << "Arguments:" << arguments;
        return true;
    }

    void beforeLoadPlugins(QSplashScreen *screen) override {
        screen->showMessage("Befor loading plugins");
    }

    void afterLoadPlugins() override {
        screen->showMessage("After loading plugins");
    }
}

int main(int argc, char *argv[]) {
    QApplication a(argc, argv);
    QMAppExtension host;

    a.setApplicationName("MyApplication");
    a.setApplicationVersion("0.0.0.1");
    a.setOrganizationName("MyOrganization");
    a.setOrganizationDomain("org.MyOrganization");

    return MyLoaderConfiguration().run();
}