单例模式与信号中心3

信号中心的实现及其注意事项。

信号中心

信号中心用来转发单例模式与信号中心1-开头问题中的信号，可大大减少信号的传递次数和函数调用的层数，其实现方式如下所示：

signalcenter.h

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#include <QObject>

class SignalCenter : public QObject
{
	Q_OBJECT
public:	
	SignalCenter(const SignalCenter&) = delete;
	SignalCenter(SignalCenter&&) = delete;

	SignalCenter& operator=(const SignalCenter&) = delete;
	SignalCenter& operator=(SignalCenter&&) = delete;
	static SignalCenter& getInstance()
	{
		static SignalCenter instance;
		return instance;
	}

private:
	SignalCenter() = default;

signals:
	void senderButtonClicked();
};
  1. 该类需继承自QObject;
  2. 使用Q_OBJECT宏并定义相关信号。

senderframe.cpp

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#include "senderframe.h"
#include <QHBoxLayout>
#include "signalcenter.h"

SenderFrame::SenderFrame(QWidget *parent) :
    QFrame(parent)
{
	init();
}

SenderFrame::~SenderFrame()
{

}

void SenderFrame::init()
{
	button_ = new QPushButton(u8"发送",this);

	QHBoxLayout* hLayout = new QHBoxLayout;
	hLayout->addWidget(button_);

	this->setLayout(hLayout);
	this->setStyleSheet("background:blue;");

	//为了演示简单，将connect写在了类里面，这样会导致该类所有的实例都会connect
	connect(button_, &QPushButton::clicked, 
		&SignalCenter::getInstance(), &SignalCenter::senderButtonClicked);
}

receiverframe.cpp

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#include "receiverframe.h"
#include <QHBoxLayout>
#include "signalcenter.h"

ReceiverFrame::ReceiverFrame(QWidget *parent) :
    QFrame(parent)
{
	init();
}

ReceiverFrame::~ReceiverFrame()
{
    
}

void ReceiverFrame::init()
{
	label_ = new QLabel(this);

	QHBoxLayout* hLayout = new QHBoxLayout;
	hLayout->addWidget(label_);

	this->setLayout(hLayout);
	this->setStyleSheet("background:green;");

	//为了演示简单，将connect写在在类里面，这样会导致该类所有的实例都会connect
	connect(&SignalCenter::getInstance(), &SignalCenter::senderButtonClicked, [=]() {
		static int i = 0;

		label_->setText(QString(u8"第%1次点击").arg(++i));
	});
}
  1. senderframe.cpp、receiverframe.cpp中各自与SignalCenter单例类connect，借助于SignalCenter单例类完成了信号的转发；
  2. 如注释所言，为了演示简单，该例将connect写在了类里面，这样会导致该类所有的实例都会connect,比如ReceiverFrame类公用，被实例化了两个实例，这样会导致点击一次按钮，两个实例都改变文字。所以将与SignalCenter单例类的connect，放到其父控件中更合适。

mainwindow.cpp

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#include "mainwindow.h"
#include "receiverframe.h"
#include "senderframe.h"
#include <QHBoxLayout>
#include <QDateTime>

MainWindow::MainWindow(QWidget *parent)
    : QDialog(parent)
{
	init();
}

MainWindow::~MainWindow()
{
    
}

void MainWindow::init()
{
	auto senderFrame = new SenderFrame(this);
	auto receiverFrame = new ReceiverFrame(this);

	QHBoxLayout* hLayout = new QHBoxLayout;
	hLayout->setContentsMargins(0, 0, 0, 0);
	hLayout->setSpacing(20);

	hLayout->addWidget(senderFrame);
	hLayout->addWidget(receiverFrame);

	this->setLayout(hLayout);
	this->setStyleSheet("background:yellow;");
	this->setFixedSize(600, 400);
}

可以看出，在mainwindow.cpp中只是实例化了SenderFrame和ReceiverFrame类，并没有connect二者，但是信号正常的由SenderFrame发送到了ReceiverFrame类。运行结果如下：