#qt

### **背景**

  
deleteLater 是 [QObject](https://so.csdn.net/so/search?q=QObject&spm=1001.2101.3001.7020) 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](https://so.csdn.net/so/search?q=%E4%BA%8B%E4%BB%B6%E5%BE%AA%E7%8E%AF&spm=1001.2101.3001.7020)，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**

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

![[Pasted image 20240806155949.png]]

### **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

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

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

demo->deleteLater();  
demo = nullptr;
```

![[Pasted image 20240806160009.png]]

#### ②．delete 则是立即删除对象，对象的既有事件不再处理

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

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

delete demo;  
demo = nullptr;
```

![[Pasted image 20240806160020.png]]

#### ③．deleteLater 后依然可以访问和操作对象，直到再次回到事件循环

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

demo->deleteLater();

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

![[Pasted image 20240806160032.png]]

### **deleteLater 和 QSharedPointer**

####   
①．概述

[智能指针](https://so.csdn.net/so/search?q=%E6%99%BA%E8%83%BD%E6%8C%87%E9%92%88&spm=1001.2101.3001.7020)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

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

###   
**deleteLater 和 moveToThread**

####   
①．概述

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

``` cpp
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);  
}
```

![[Pasted image 20240806160059.png]]

#### ②．利用 deleteLater 进行资源清理

``` cpp
//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 );
```