Qt 中 deleteLater 使用总结

背景

deleteLater 是 QObject 类对象的成员函数，用于延迟删除一个 QObject 类对象，且对 QObject 类对象的删除推荐使用 deleteLater 而非 delete 。

deleteLater

①．概述

deleteLater 依赖于事件循环，调用 deleteLater 后本质是发送了一个 DeferrerDelete 事件，在事件循环处理中把对象删除。

②．代码示例

demo = new QtClassDemo(this);
demo->deleteLater();
demo = nullptr;

deleteLater 和 delete

①．deleteLater 会在当前对象的所有事件处理完成后再删除对象

demo = new QtClassDemo(this);
demo->setObjectName("demo");

qApp->postEvent(demo, new CustomEvent("hello"));
qApp->postEvent(demo, new CustomEvent("world"));

demo->deleteLater();
demo = nullptr;

②．delete 则是立即删除对象，对象的既有事件不再处理

demo = new QtClassDemo(this);
demo->setObjectName("demo");

qApp->postEvent(demo, new CustomEvent("hello"));
qApp->postEvent(demo, new CustomEvent("world"));

delete demo;
demo = nullptr;

③．deleteLater 后依然可以访问和操作对象，直到再次回到事件循环

demo = new QtClassDemo(this);
demo->setObjectName("demo");

demo->deleteLater();

qDebug() << demo->objectName();
demo = nullptr;

deleteLater 和 QSharedPointer

①．概述

智能指针可以传入自定义的删除器，对于继承自 QObject 的类对象可以传入 deleteLater 。

②．代码示例

QSharedPointer<QtClassDemo> demoClass(new QtClassDemo(this), &QObject::deleteLater);

deleteLater 和 moveToThread

①．概述

moveToThread 的本质是把 QObject 对象到事件循环移动到子线程进行处理：

qDebug() << "主线程:"<< QThread::currentThread();
QThread * workThread = new QThread;

demo = new QtClassDemo(nullptr);
demo->setObjectName("demo");
demo->moveToThread(workThread);
workThread->start();

bool QtClassDemo::event(QEvent * event)
{
    
  qDebug() << "事件处理线程:"<< QThread::currentThread() << event->type();

  return QObject::event(event);
}

②．利用 deleteLater 进行资源清理

//工作对象工作完成，停止线程
QObject::connect(workObject,&WorkObject::workFinished,[&](){
    
    workThread->quit();
    workThread->wait();
});
//工作线程停止，删除工作对象
QObject::connect(workThread,&QThread::finished,workObject,&WorkObject::deleteLater );
//工作对象销毁，删除工作线程
QObject::connect(workObject,&WorkObject::destroyed,workThread,&QThread::deleteLater );