我们有时候想发送自定义事件

1：创建自定义事件，首先我们需要知道它的条件

1：自定义事件需要继承QEvent
2：事件的类型需要在 QEvent::User 和 QEvent::MaxUser 范围之间，在QEvent::User之前 是预留给系统的事件
3：使用sendEvent() 和 postEvent()发送自定义消息
4：接受自定义消息，通过 重写 customEvent 或者 使用 eventFilter事件 来处理

2：注册自定义事件ID

在注册自定义事件的时候我们有两种方法
一：使用QEvent::registerEventType()，这个是系统会帮助我们注册ID，如果错误 返回-1
二：我们自定义 取QEvent::User 和QEvent::MaxUser 之间的值

方法一：
QEvent::Type CustomEvent::m_eventType = (QEvent::Type)QEvent::registerEventType();方法二：
const int CustomEventBaseID = QEvent::User;
const int TextEventID = CustomEventBaseID + 1;

3：自定义事件

class CustomEvent :public QEvent
{
public:CustomEvent();virtual ~CustomEvent();static QEvent::Type eventType();
private:static QEvent::Type m_eventType;
};

QEvent::Type CustomEvent::m_eventType = (QEvent::Type)QEvent::registerEventType();//1、注册自定义事件类型CustomEvent::CustomEvent():QEvent(eventType()) //2、指定事件类型
{}CustomEvent::~CustomEvent()
{}QEvent::Type CustomEvent::eventType()
{return m_eventType;
}

4:发送自定义事件

postEvent 方法：异步发送，向事件队列中 的发送一个指定接受者事件
不需要手动释放事件的内存，QT框架自动释放

sendEvent方法：此方法是阻塞发送的，它发送对象事件，等待对象处理结束返回；
需要手动释放事件的内存

5：自定义事件处理

写自定义事件 void customEvent(QEvent* event) override;

写事件过滤器 bool eventFilter(QObject* watched, QEvent* event) override;
还需要将对象添加到事件过滤器中

源码：
.h

#pragma once#include <QtWidgets/QWidget>
#include "ui_CustomEventTest.h"
#include <QEvent>
#include <QDebug>//自定义事件
class CustomEvent :public QEvent
{
public:CustomEvent();virtual ~CustomEvent();void SetText(const QString& str);QString GetText() const;void SetNumber(int number);int GetNumber() const;static QEvent::Type eventType();
private:QString m_str;int m_number;static QEvent::Type m_eventType;
};class CustomTwoEvent :public QEvent
{
public:CustomTwoEvent();virtual ~CustomTwoEvent();void SetStr(const QString& str);QString GetStr() const;void SetNumber(int number);int GetNumber() const;
private:QString m_str;int m_number;};//测试自定义事件
class CustomEventTest : public QWidget
{Q_OBJECTpublic:CustomEventTest(QWidget *parent = nullptr);~CustomEventTest();private slots://测试自定义事件一void on_btn1_1_clicked();void on_btn2_1_clicked();void on_btn3_1_clicked();void on_btn4_1_clicked();protected:void customEvent(QEvent* event) override;private slots://测试自定义事件二void on_btn5_1_clicked();void on_btn6_1_clicked();void on_btn7_1_clicked();void on_btn8_1_clicked();protected:bool eventFilter(QObject* watched, QEvent* event) override;private:Ui::CustomEventTestClass ui;
};

.cpp

#include "CustomEventTest.h"/************************自定义事件一********************************/
QEvent::Type CustomEvent::m_eventType = (QEvent::Type)QEvent::registerEventType();//1、注册自定义事件类型CustomEvent::CustomEvent():QEvent(eventType()) //2、指定事件类型
{}CustomEvent::~CustomEvent()
{}void CustomEvent::SetText(const QString& str)
{m_str = str;
}QString CustomEvent::GetText() const
{return m_str;
}void CustomEvent::SetNumber(int number)
{m_number = number;
}int CustomEvent::GetNumber() const
{return m_number;
}QEvent::Type CustomEvent::eventType()
{return m_eventType;
}/************************自定义事件一********************************//************************自定义事件二********************************/const int CustomEventBaseID = QEvent::User;
const int TextEventID = CustomEventBaseID + 1;CustomTwoEvent::CustomTwoEvent():QEvent(QEvent::Type(TextEventID))
{}CustomTwoEvent::~CustomTwoEvent()
{}void CustomTwoEvent::SetStr(const QString& str)
{m_str = str;
}QString CustomTwoEvent::GetStr() const
{return m_str;
}void CustomTwoEvent::SetNumber(int number)
{m_number = number;
}int CustomTwoEvent::GetNumber() const
{return m_number;
}/************************自定义事件二********************************//************************测试自定义事件********************************/
CustomEventTest::CustomEventTest(QWidget *parent): QWidget(parent)
{ui.setupUi(this);qApp->installEventFilter(this);
}CustomEventTest::~CustomEventTest()
{}void CustomEventTest::on_btn1_1_clicked()
{QString str = QStringLiteral("自定义事件一 我是post 发送指针");CustomEvent* event = new CustomEvent;event->SetText(str);event->SetNumber(1);qApp->postEvent(this, event);
}void CustomEventTest::on_btn2_1_clicked()
{QString str = QStringLiteral("自定义事件一  我是post 发送局部变量");CustomEvent event;event.SetText(str);event.SetNumber(2);//会出现崩溃qApp->postEvent(this, &event);
}void CustomEventTest::on_btn3_1_clicked()
{QString str = QStringLiteral("自定义事件一  我是send 发送指针");CustomEvent* event = new CustomEvent;event->SetText(str);event->SetNumber(3);qApp->sendEvent(this, event);delete event;
}void CustomEventTest::on_btn4_1_clicked()
{QString str = QStringLiteral("自定义事件一  我是send 发送局部变量");CustomEvent event;event.SetText(str);event.SetNumber(4);qApp->sendEvent(this, &event);
}void CustomEventTest::on_btn5_1_clicked()
{QString str = QStringLiteral("自定义事件二  我是post 发送指针");CustomTwoEvent* event = new CustomTwoEvent;event->SetStr(str);event->SetNumber(5);qApp->postEvent(this, event);
}void CustomEventTest::on_btn6_1_clicked()
{QString str = QStringLiteral("自定义事件二  我是post 发送局部变量");CustomTwoEvent event;event.SetStr(str);event.SetNumber(6);//会出现崩溃qApp->postEvent(this, &event);
}void CustomEventTest::on_btn7_1_clicked()
{QString str = QStringLiteral("自定义事件二  我是send 发送指针");CustomTwoEvent* event = new CustomTwoEvent;event->SetStr(str);event->SetNumber(7);qApp->sendEvent(this, event);delete event;
}void CustomEventTest::on_btn8_1_clicked()
{QString str = QStringLiteral("自定义事件二  我是send 发送局部变量");CustomTwoEvent event;event.SetStr(str);event.SetNumber(8);qApp->sendEvent(this, &event);
}void CustomEventTest::customEvent(QEvent* event)
{if (event->type() == CustomEvent::eventType()){CustomEvent* e = dynamic_cast<CustomEvent*>(event);if (e->GetNumber() == 1)ui.btn1->setText(e->GetText());else if (e->GetNumber() == 2)ui.btn2->setText(e->GetText());else if (e->GetNumber() == 3)ui.btn3->setText(e->GetText());else if (e->GetNumber() == 4)ui.btn4->setText(e->GetText());}
}bool CustomEventTest::eventFilter(QObject* watched, QEvent* event)
{if (event->type() == TextEventID){CustomTwoEvent* e = dynamic_cast<CustomTwoEvent*>(event);if (e->GetNumber() == 5)ui.btn5->setText(e->GetStr());else if (e->GetNumber() == 6)ui.btn6->setText(e->GetStr());else if (e->GetNumber() == 7)ui.btn7->setText(e->GetStr());else if (e->GetNumber() == 8)ui.btn8->setText(e->GetStr());event->accept();}return QWidget::eventFilter(watched,event);
}
/************************测试自定义事件********************************/

错误：在上面的代码中，当我们post 局部变量的时候会出现错误

QCoreApplication::removePostedEvent: Event of type 65535 deleted while posted to CustomEventTest CustomEventTestClass

原因：postEvent 只能在堆上创建，系统会自动释放

参考博客：
Qt 自定义事件
Qt中的事件- 自定义事件
Qt事件：自定义事件