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QSignalMapper类可以看成是信号的翻译和转发器。
它可以把一个无参的信号翻译成带以下4种参数的信号再转发：int、QString、 QObject以及QWidget 。

应用场景一般是：有一些信号，发送的参数都是一样的情况下，常用的方法是给每一个信号都连接一个槽函数。但这样做，会让代码多一些不必要的复杂，这种情况下，你就可以使用QSignalMapper

下面是 3 个按钮连接 到 对应的 映射数据
setMapping 设置 发射对象 接受的数据

意思：m_signalMapper 作为一个中转站 点击按钮 给到 m_signalMapper，用map来翻译 这个 数据，然后m_signalMapper 发射mapped信号 将刚才翻译的数据发送给 this，这个this 就是我们最终的 接受者
目的：这时候我们就将3个按钮的点击信号 都交给 m_signalMapper 去处理，它发射一个信号mapped 就 节省了 3个按钮 都需要写connect 非必要操作，因为他们的 目的 都是 去 触发showName 这个槽函数，现在我们只需要一个 conenct 就可以解决

	m_signalMapper = new QSignalMapper(this);

	m_signalMapper->setMapping(ui.btn1, "Button 1 clicked");
	m_signalMapper->setMapping(ui.btn2, "Button 2 clicked");
	m_signalMapper->setMapping(ui.btn3, "Button 3 clicked");

	connect(ui.btn1, SIGNAL(clicked()), m_signalMapper, SLOT(map()));
	connect(ui.btn2, SIGNAL(clicked()), m_signalMapper, SLOT(map()));
	connect(ui.btn3, SIGNAL(clicked()), m_signalMapper, SLOT(map()));

	connect(m_signalMapper, SIGNAL(mapped(const QString&)), this, SLOT(showName(const QString&)));
	connect(m_signalMapper, SIGNAL(mapped(QString)), this, SLOT(showStrName(QString)));

结果：

来看一下如果参数为 QObejct是怎么回事

这里有一个StudentInfo 类型 是继承于QObject的，然后分别设置了它的参数，此时我们就知道，点击按钮，然后将 这个学生的信息 交给我们的 m_signalMapper，然后它 在转发给我们的 showStudentInfo 函数，这里函数展示了我们学生的信息情况，也同样不需要写 3个 connect 来操作

	m_s1.SetName("lion");
	m_s1.SetAge(20);

	StudentInfo* s2 = new StudentInfo("cxq", 18);
	StudentInfo* s3 = new StudentInfo("lion_cxq", 22);

	m_signalMapper->setMapping(ui.btn1, &m_s1);
	m_signalMapper->setMapping(ui.btn2, s2);
	m_signalMapper->setMapping(ui.btn3, s3);

	connect(ui.btn1, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));
	connect(ui.btn2, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));
	connect(ui.btn3, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));

	connect(m_signalMapper, QOverload<QObject*>::of(&QSignalMapper::mapped), this, &QSignalMapperTest::showStudentInfo);

关键的一点是：
我们可以在槽函数中 将QObject 转化为我们 自定义的指针

void QSignalMapperTest::showStudentInfo(QObject* object)
{
	StudentInfo* s = qobject_cast<StudentInfo*>(object);
	if (s)
	{
		qDebug() << s->GetAge() << s->GetName();
	}
}

还有一个就是我们遇到同名的 槽函数时，我们必须要同时两边重载，使用一个即可，否则会报错

	//第一个
	connect(m_signalMapper, QOverload<const QString&>::of(&QSignalMapper::mapped), this, QOverload<const QString&>::of(&QSignalMapperTest::showName));
	//第二个
	connect(m_signalMapper, static_cast<void (QSignalMapper::*)(const QString&)>(&QSignalMapper::mapped), this, static_cast<void (QSignalMapperTest::*)(const QString&)>
(&QSignalMapperTest::showName));

结果：

完整代码：
ui图

.h

#pragma once

#include <QtWidgets/QWidget>
#include "ui_QSignalMapperTest.h"
#include <QSignalMapper>
#include <QDebug>
#include <QVariant>

#define QT5

typedef struct Student
{
	QString name;
	int age;
}Student;
Q_DECLARE_METATYPE(Student)

class StudentInfo :public QObject
{
	Q_OBJECT
public:
	StudentInfo(QObject* parent = nullptr);
	StudentInfo(QString name, int age, QObject* parent = nullptr);

	void SetName(const QString&);
	QString GetName() const;

	void SetAge(const int&);
	int GetAge() const;

private:
	QString m_name;
	int m_age;
};

class QSignalMapperTest : public QWidget
{
    Q_OBJECT

public:
    QSignalMapperTest(QWidget *parent = Q_NULLPTR);

public Q_SLOTS:
	void showName(const QString&);
	void showName(QString, int);
	void showStrName(QString);
	void showStudentInfo(QObject* object);


private:
    Ui::QSignalMapperTestClass ui;

	StudentInfo m_s1;
	QSignalMapper* m_signalMapper;
};

.cpp

#include "QSignalMapperTest.h"

QSignalMapperTest::QSignalMapperTest(QWidget *parent)
    : QWidget(parent)
{
    ui.setupUi(this);

	m_signalMapper = new QSignalMapper(this);

#if 1
	#ifdef QT5
	m_s1.SetName("lion");
	m_s1.SetAge(20);

	StudentInfo* s2 = new StudentInfo("cxq", 18);
	StudentInfo* s3 = new StudentInfo("lion_cxq", 22);

	m_signalMapper->setMapping(ui.btn1, &m_s1);
	m_signalMapper->setMapping(ui.btn2, s2);
	m_signalMapper->setMapping(ui.btn3, s3);

	connect(ui.btn1, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));
	connect(ui.btn2, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));
	connect(ui.btn3, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));

	connect(m_signalMapper, QOverload<QObject*>::of(&QSignalMapper::mapped), this, &QSignalMapperTest::showStudentInfo);
	#else
	StudentInfo* s = new StudentInfo("cxq", 18);

	m_signalMapper->setMapping(ui.btn1, s);
	m_signalMapper->setMapping(ui.btn2, s);
	m_signalMapper->setMapping(ui.btn3, s);

	connect(ui.btn1, SIGNAL(clicked()), m_signalMapper, SLOT(map()));
	connect(ui.btn2, SIGNAL(clicked()), m_signalMapper, SLOT(map()));
	connect(ui.btn3, SIGNAL(clicked()), m_signalMapper, SLOT(map()));

	connect(m_signalMapper, SIGNAL(mapped(QObject*)), this, SLOT(showStudentInfo(QObject*)));
	#endif
#endif

#if 0
	#ifdef QT5
	m_signalMapper->setMapping(ui.btn1, "Button 1 clicked");
	m_signalMapper->setMapping(ui.btn2, "Button 2 clicked");
	m_signalMapper->setMapping(ui.btn3, "Button 3 clicked");

	connect(ui.btn1, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));
	connect(ui.btn2, &QPushButton::clicked, m_signalMapper, QOverload<>::of(&QSignalMapper::map));
	connect(ui.btn3, &QPushButton::clicked, m_signalMapper, static_cast<void(QSignalMapper::*)()>(&QSignalMapper::map));

	//使用这个报错  必须使用下面第一种或者第二种  因为 槽函数也是重载的
	//connect(m_signalMapper, QOverload<const QString&>::of(&QSignalMapper::mapped), this, &QSignalMapperTest::showName);
	//第一个
	//connect(m_signalMapper, QOverload<const QString&>::of(&QSignalMapper::mapped), this, QOverload<const QString&>::of(&QSignalMapperTest::showName));
	//第二个
	connect(m_signalMapper, static_cast<void (QSignalMapper::*)(const QString&)>(&QSignalMapper::mapped), this, static_cast<void (QSignalMapperTest::*)(const QString&)>(&QSignalMapperTest::showName));
	#else
	m_signalMapper->setMapping(ui.btn1, "Button 1 clicked");
	m_signalMapper->setMapping(ui.btn2, "Button 2 clicked");
	m_signalMapper->setMapping(ui.btn3, "Button 3 clicked");

	connect(ui.btn1, SIGNAL(clicked()), m_signalMapper, SLOT(map()));
	connect(ui.btn2, SIGNAL(clicked()), m_signalMapper, SLOT(map()));
	connect(ui.btn3, SIGNAL(clicked()), m_signalMapper, SLOT(map()));

	//可以
	connect(m_signalMapper, SIGNAL(mapped(const QString&)), this, SLOT(showName(const QString&)));
	connect(m_signalMapper, SIGNAL(mapped(QString)), this, SLOT(showStrName(QString)));
	//不可以  多个参数不可以
	//connect(m_signalMapper, SIGNAL(mapped(QString,int)), this, SLOT(showName(QString,int)));
	#endif
#endif
}

void QSignalMapperTest::showName(const QString& str)
{
	qDebug() << str;
}

void QSignalMapperTest::showName(QString name, int age)
{
	qDebug() << QStringLiteral("姓名:");
}

void QSignalMapperTest::showStrName(QString str)
{
	qDebug() << str;
}

void QSignalMapperTest::showStudentInfo(QObject* object)
{
	StudentInfo* s = qobject_cast<StudentInfo*>(object);
	if (s)
	{
		qDebug() << s->GetAge() << s->GetName();
	}
}

StudentInfo::StudentInfo(QObject* parent)
{

}

StudentInfo::StudentInfo(QString name, int age, QObject* parent )
{
	m_name = name;
	m_age = age;
}

void StudentInfo::SetName(const QString& name )
{
	m_name = name;
}

QString StudentInfo::GetName() const
{
	return m_name;
}

void StudentInfo::SetAge(const int& age)
{
	m_age = age;
}

int StudentInfo::GetAge() const
{
	return m_age;
}

参考博客：
QSignalMapper介绍
QSignalMapper使用