Can Qt signals return a value?

Question

Boost.Signals allows various strategies of using the return values of slots to form the return value of the signal. E.g. adding them, forming a vector out of th

Answer 1

You may get a return value from Qt signal with the following code:

My example shows how to use a Qt signal to read the text of a QLineEdit. I'm just extending what @jordan has proposed:

It should be possible to modify your code in such a way to use "out" parameters that act as your "return".

#include 
#include 

class SignalsRet : public QObject
{
    Q_OBJECT

public:
    SignalsRet()
    {
        connect(this, SIGNAL(Get(QString*)), SLOT(GetCurrentThread(QString*)), Qt::DirectConnection);
        connect(this, SIGNAL(GetFromAnotherThread(QString*)), SLOT(ReadObject(QString*)), Qt::BlockingQueuedConnection);
        edit.setText("This is a test");
    }

public slots:
    QString call()
    {
        QString text;
        emit Get(&text);
        return text;
    }

signals:
    void Get(QString *value);
    void GetFromAnotherThread(QString *value);

private slots:
    void GetCurrentThread(QString *value)
    {
        QThread *thread = QThread::currentThread();
        QThread *mainthread = this->thread();
        if(thread == mainthread) //Signal called from the same thread that SignalsRet class was living
            ReadObject(value);
        else //Signal called from another thread
            emit GetFromAnotherThread(value);
    }

    void ReadObject(QString *value)
    {
        QString text = edit.text();
        *value = text;
    }

private:
    QLineEdit edit;

};

To use this, just request call();.