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这里以Qt Creator 4.15.2版本的源码为示例进行分析

源码结构如下，为了追溯其插件加载过程，从main.cpp入手

Qt Creator的插件目录，生成的插件，好几十个呢

 Qt Creator插件的读取

int main(int argc, char **argv)中以下代码创建插件的管理

    PluginManager pluginManager;PluginManager::setPluginIID(QLatin1String("org.qt-project.Qt.QtCreatorPlugin"));PluginManager::setGlobalSettings(globalSettings);PluginManager::setSettings(settings);

 int main(int argc, char **argv)中以下设置插件的读取目录，读取所有插件信息

    const QStringList pluginPaths = getPluginPaths() + options.customPluginPaths;PluginManager::setPluginPaths(pluginPaths);//读取插件目录下的插件

从 PluginManager::setPluginPaths(pluginPaths)调用追溯到如下

void PluginManagerPrivate::setPluginPaths(const QStringList &paths)
{qCDebug(pluginLog) << "Plugin search paths:" << paths;qCDebug(pluginLog) << "Required IID:" << pluginIID;pluginPaths = paths;readSettings();readPluginPaths();
}

继续追溯void PluginManagerPrivate::readPluginPaths()

    for (const QString &pluginFile : pluginFiles(pluginPaths)) {PluginSpec *spec = PluginSpec::read(pluginFile);

PluginSpec *PluginSpec::read(const QString &filePath)
{auto spec = new PluginSpec;if (!spec->d->read(filePath)) { // not a Qt Creator plugindelete spec;return nullptr;}return spec;
}

其中bool PluginSpecPrivate::read(const QString &fileName)方法读取了插件的基本信息

Qt Creator 加载插件

从main函数中的 PluginManager::loadPlugins();开始追溯插件的加载

void PluginManagerPrivate::loadPlugins()
{//所有插件都会从loaded-->initialized-->runningconst QVector<PluginSpec *> queue = loadQueue();Utils::setMimeStartupPhase(MimeStartupPhase::PluginsLoading);for (PluginSpec *spec : queue)loadPlugin(spec, PluginSpec::Loaded);Utils::setMimeStartupPhase(MimeStartupPhase::PluginsInitializing);for (PluginSpec *spec : queue)loadPlugin(spec, PluginSpec::Initialized);Utils::setMimeStartupPhase(MimeStartupPhase::PluginsDelayedInitializing);Utils::reverseForeach(queue, [this](PluginSpec *spec) {loadPlugin(spec, PluginSpec::Running);//从这里开始加载插件...step2if (spec->state() == PluginSpec::Running) {delayedInitializeQueue.push(spec);} else {// Plugin initialization failed, so cleanup after itspec->d->kill();}});...
}

插件加载的几个主要步骤，load, initialize, run

在 void PluginManagerPrivate::loadPlugin(PluginSpec *spec, PluginSpec::State destState)中

    switch (destState) {case PluginSpec::Loaded:profilingReport(">loadLibrary", spec);spec->d->loadLibrary();profilingReport("<loadLibrary", spec);break;case PluginSpec::Initialized:profilingReport(">initializePlugin", spec);spec->d->initializePlugin();profilingReport("<initializePlugin", spec);break;case PluginSpec::Stopped:profilingReport(">stop", spec);if (spec->d->stop() == IPlugin::AsynchronousShutdown) {asynchronousPlugins << spec;connect(spec->plugin(), &IPlugin::asynchronousShutdownFinished,this, &PluginManagerPrivate::asyncShutdownFinished);}profilingReport("<stop", spec);break;default:break;}

继续追溯bool PluginSpecPrivate::loadLibrary()

    if (!loader.load()) {//这里是加载插件hasError = true;errorString = QDir::toNativeSeparators(filePath)+ QString::fromLatin1(": ") + loader.errorString();return false;}

Qt Creator插件

合格的插件需要继承自IPlugin抽象类

以CppEditorPlugin为例

class CppEditorPlugin : public ExtensionSystem::IPlugin

看一下IPlugin类

#pragma once#include "extensionsystem_global.h"#include <QObject>namespace ExtensionSystem {namespace Internal {class IPluginPrivate;class PluginSpecPrivate;
}class PluginManager;
class PluginSpec;class EXTENSIONSYSTEM_EXPORT IPlugin : public QObject
{Q_OBJECTpublic:enum ShutdownFlag {SynchronousShutdown,AsynchronousShutdown};IPlugin();~IPlugin() override;virtual bool initialize(const QStringList &arguments, QString *errorString) = 0;virtual void extensionsInitialized() {}virtual bool delayedInitialize() { return false; }virtual ShutdownFlag aboutToShutdown() { return SynchronousShutdown; }virtual QObject *remoteCommand(const QStringList & /* options */,const QString & /* workingDirectory */,const QStringList & /* arguments */) { return nullptr; }virtual QVector<QObject *> createTestObjects() const;PluginSpec *pluginSpec() const;signals:void asynchronousShutdownFinished();private:Internal::IPluginPrivate *d;friend class Internal::PluginSpecPrivate;
};} // namespace ExtensionSystem

 实现具体的插件类时，以下方法是必须重写的

virtual bool initialize(const QStringList &arguments, QString *errorString) = 0;