Qt程序单次启动（QSingleApplication类）

一介绍

通过编写一个QSingleApplication类，来实现Qt程序的单例化，原文的作者是在Windows Vista +Qt4.4 下实现的，不过应用在其他平台上是没问题的。(本文是我在http://www.qtcentre.org/wiki/index.php?title=SingleApplication上看到的)

二代码

方案一：使用Qt中的QSharedMemory,QLocalServer和QLocalSocket实现(不过需要在你的.pro里加上QT += network)

别的没翻译，就是大概说了一下，直接来代码吧：

// "single_application.h"

#ifndef SINGLE_APPLICATION_H
#define SINGLE_APPLICATION_H

#include <QApplication>
#include <QSharedMemory>
#include <QLocalServer>

class SingleApplication : public QApplication

{
    Q_OBJECT
public:

    SingleApplication(int &argc, char *argv[], const QString uniqueKey);
    bool isRunning();
    bool sendMessage(const QString &message);
public slots:
    void receiveMessage();
signals:
    void messageAvailable(QString message);
private:
    bool _isRunning;
    QString _uniqueKey;
    QSharedMemory sharedMemory;
    QLocalServer *localServer;
    static const int timeout = 1000;
};

#endif // SINGLE_APPLICATION_H

// "single_application.cpp"
#include <QLocalSocket>
#include "single_application.h"

SingleApplication::SingleApplication(int &argc, char *argv[], const QString uniqueKey) : QApplication(argc, argv), _uniqueKey(uniqueKey)

{
    sharedMemory.setKey(_uniqueKey);
    if (sharedMemory.attach())
        _isRunning = true;
    else
    {
        _isRunning = false;
        // create shared memory.
        if (!sharedMemory.create(1))
        {
            qDebug("Unable to create single instance.");
            return;
        }

        // create local server and listen to incomming messages from other instances.
        localServer = new QLocalServer(this);
        connect(localServer, SIGNAL(newConnection()), this, SLOT(receiveMessage()));
        localServer->listen(_uniqueKey);
    }
}

// public slots.
void SingleApplication::receiveMessage()
{
    QLocalSocket *localSocket = localServer->nextPendingConnection();
    if (!localSocket->waitForReadyRead(timeout))
    {
        qDebug(localSocket->errorString().toLatin1());
        return;
    }

    QByteArray byteArray = localSocket->readAll();
    QString message = QString::fromUtf8(byteArray.constData());
    emit messageAvailable(message);
    localSocket->disconnectFromServer();
}

// public functions.
bool SingleApplication::isRunning()
{
    return _isRunning;
}

bool SingleApplication::sendMessage(const QString &message)
{
    if (!_isRunning)
        return false;
    QLocalSocket localSocket(this);
    localSocket.connectToServer(_uniqueKey, QIODevice::WriteOnly);
    if (!localSocket.waitForConnected(timeout))
    {
        qDebug(localSocket.errorString().toLatin1());
        return false;
    }

    localSocket.write(message.toUtf8());
    if (!localSocket.waitForBytesWritten(timeout))
    {
        qDebug(localSocket.errorString().toLatin1());
        return false;
    }

    localSocket.disconnectFromServer();
    return true;

方案二：使用Qt中的QSharedMemory,和QTimert实现,别的也没翻译，还是直接来代码吧：

// "single_application.h"
#ifndef SINGLE_APPLICATION_H
#define SINGLE_APPLICATION_H

#include <QApplication>
#include <QSharedMemory>

class SingleApplication : public QApplication
{
    Q_OBJECT
public:
    SingleApplication(int &argc, char *argv[], const QString uniqueKey);
    bool isRunning();
    bool sendMessage(const QString &message);
public slots:
    void checkForMessage();
signals:
    void messageAvailable(QString message);
private:
    bool _isRunning;
    QSharedMemory sharedMemory;
};

#endif // SINGLE_APPLICATION_H

// "single_application.cpp"
#include <QTimer>
#include <QByteArray>
#include "single_application.h"

SingleApplication::SingleApplication(int &argc, char *argv[], const QString uniqueKey) : QApplication(argc, argv)
{
    sharedMemory.setKey(uniqueKey);
    if (sharedMemory.attach())
        _isRunning = true;
    else
    {
        _isRunning = false;
        // attach data to shared memory.
        QByteArray byteArray("0"); // default value to note that no message is available.
        if (!sharedMemory.create(byteArray.size()))
        {
            qDebug("Unable to create single instance.");
            return;
        }
        sharedMemory.lock();
        char *to = (char*)sharedMemory.data();
        const char *from = byteArray.data();
        memcpy(to, from, qMin(sharedMemory.size(), byteArray.size()));
        sharedMemory.unlock();

                // start checking for messages of other instances.
        QTimer *timer = new QTimer(this);
        connect(timer, SIGNAL(timeout()), this, SLOT(checkForMessage()));
        timer->start(1000);
    }
}

// public slots.
void SingleApplication::checkForMessage()
{
    sharedMemory.lock();
    QByteArray byteArray = QByteArray((char*)sharedMemory.constData(), sharedMemory.size());
    sharedMemory.unlock();
    if (byteArray.left(1) == "0")
        return;
    byteArray.remove(0, 1);
    QString message = QString::fromUtf8(byteArray.constData());
    emit messageAvailable(message);

        // remove message from shared memory.
    byteArray = "0";
    sharedMemory.lock();
    char *to = (char*)sharedMemory.data();
    const char *from = byteArray.data();
    memcpy(to, from, qMin(sharedMemory.size(), byteArray.size()));
    sharedMemory.unlock();
}

// public functions.
bool SingleApplication::isRunning()
{
    return _isRunning;
}

bool SingleApplication::sendMessage(const QString &message)
{
    if (!_isRunning)
        return false;

    QByteArray byteArray("1");
    byteArray.append(message.toUtf8());
    byteArray.append('/0'); // < should be as char here, not a string!
    sharedMemory.lock();
    char *to = (char*)sharedMemory.data();
    const char *from = byteArray.data();
    memcpy(to, from, qMin(sharedMemory.size(), byteArray.size()));
    sharedMemory.unlock();
    return true;
}

三使用

// "main.cpp"
#include "single_application.h"
int main(int argc, char *argv[])
{
    SingleApplication app(argc, argv, "some unique key string");
    if (app.isRunning())
    {
        app.sendMessage("message from other instance.");
        return 0;
    }

    MainWindow *mainWindow = new MainWindow();

        // connect message queue to the main window.
    QObject::connect(&app, SIGNAL(messageAvailable(QString)), mainWindow, SLOT(receiveMessage(QString)));

        // show mainwindow.
    mainWindow->show();
    return app.exec();

}

亲测可用。
原文地址：https://blog.csdn.net/playstudy/article/details/7796691