Disconnecting signals fails - c++

Question

In my code I want to reroute a signal-slot-connection, i.e. first the slot is connected to signal 1, and after the rerouting it should only be connected to signal 2. For that I used disconnect(this), with this referring to the class which owns the slots (it is in a class function). This command should disconnect all signals from extern from the class. Unfortunately, I get false as return value of disconnect(). Why can't I disconnect the signals? Is there a possibility to get more information?
Strangely, in my example below the disconnect and reconnect does not work, too, I get the same error code from disconnect.
If I remove the line connect(this, &MainWindow::writeLine, class1, &TXClass::emit_signal); from the on_PushButton2_clicked()-function, disconnect() still returns "false", but I get the expected result.
Example code:
Mainwindow.cpp:
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
class1 = new TXClass("Class 1");
class2 = new TXClass("Class 2");
connect(this, SIGNAL(writeLine()), class1, SLOT(emit_signal()));
connect(class1, SIGNAL(signal(QString)), this, SLOT(newText(QString)));
}
MainWindow::~MainWindow()
{
delete class1;
delete class2;
delete ui;
}
void MainWindow::newText(QString text)
{
ui->lineEdit->setText(text);
}
void MainWindow::on_pushButton_clicked()
{
emit writeLine();
}
void MainWindow::on_pushButton_2_clicked()
{
qDebug() << "Disconnect result: " << disconnect(this);
connect(this, &MainWindow::writeLine, class2, &TXClass::emit_signal);
connect(this, &MainWindow::writeLine, class1, &TXClass::emit_signal);
connect(class2, &TXClass::signal, this, &MainWindow::newText);
//The onliest signal I want to get now is from class2.
}
MainWindow.h:
#include <QDebug>
#include <txclass.h>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
signals:
void writeLine(void);
public slots:
void on_pushButton_clicked();
void newText(QString text);
void on_pushButton_2_clicked();
private:
Ui::MainWindow *ui;
TXClass *class1, *class2;
};
#endif // MAINWINDOW_H
TXClass.cpp:
#include "txclass.h"
TXClass::TXClass(QString name)
{
TXClass::name = name;
}
void TXClass::emit_signal()
{
emit signal(name);
}
TXClass.h:
#ifndef TXCLASS_H
#define TXCLASS_H
#include <QObject>
class TXClass : public QObject
{
Q_OBJECT
private:
QString name;
signals:
void signal(QString string);
public slots:
void emit_signal(void);
public:
TXClass(QString name);
};
#endif // TXCLASS_H

Answer 1

I've checked how QObject::disconnect is implemented and I don't see how this is supposed to work if you only specify receiver. QMetaObjectPrivate::disconnect will return immediately with false when sender is not specified. This means that second part of QObject::disconnect will no set res to true. The only other place you could get true out of is call to QInternal::activateCallbacks. But it doesn't look like it's instance specific, rather some global stuff (I admit I have no idea what exactly is this suppose to do :/).
I solution that works and seems good enough is this:
void MainWindow::second()
{
qDebug() << "Disconnect result: " << class1->disconnect();
connect(this, &MainWindow::writeLine, class2, &TXClass::emit_signal);
connect(this, &MainWindow::writeLine, class1, &TXClass::emit_signal);
connect(class2, &TXClass::signal, this, &MainWindow::newText);
//The onliest signal I want to get now is from class2.
}