Connecting to slot by string name

poor_robert

Hello I have following code:

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
	Q_OBJECT

public:
	explicit MainWindow(QWidget *parent = 0);
	~MainWindow();

signals:
	void testSignal();

public slots:
	void testSlot();

private:
	Ui::MainWindow *ui;
};

MainWindow::MainWindow(QWidget *parent) :
	QMainWindow(parent),
	ui(new Ui::MainWindow)
{
	ui->setupUi(this);

	bool result = false;
	result = connect(this, SIGNAL(testSignal()), this, SLOT("testSlot()"));
	qDebug() << result;
}

MainWindow::~MainWindow()
{
	delete ui;
}

void MainWindow::testSlot()
{

}

but when I ran it I get:

QObject::connect: No such slot MainWindow::"testSlot()" in ../connections/MainWindow.cpp:14
QObject::connect: (sender name: 'MainWindow')
QObject::connect: (receiver name: 'MainWindow')
false

Can you tell me how to properly connect to the slot by its string name? I know hot to use signal and slots but I have no idea how to force it work with the slot name passed by name.

BR,
poorBob

m.sue

Hi @poor_robert

The problem is the namespace you use. Remove it and it will work.

-Michael.

poor_robert

Hello @m-sue ,

which namespace? MainWindow? How to remove it then?

artwaw

@poor_robert said in Connecting to slot by string name:

SLOT("testSlot()"));

Should be SLOT(testSlot())); methinks.

m.sue

Hi @poor_robert

This one:

namespace Ui {
class MainWindow;
}

-Michael.

poor_robert

@artwaw
of course you're right, but in this case I want to know how to connect with slot name in parenthesis so SLOT("testSlot()")); is exactly what I want to try.

@m-sue :
I have simplified the code:

class MainWindow : public QObject
{
	Q_OBJECT

public:
	explicit MainWindow(QObject *parent = 0);
	~MainWindow();

signals:
	void testSignal();

public slots:
	void testSlot();
};


#include "MainWindow.h"

#include <QDebug>

MainWindow::MainWindow(QObject *parent)
{
	bool result = false;
	result = connect(this, SIGNAL(testSignal()), this, SLOT("testSlot()"));
	qDebug() << result;
}

MainWindow::~MainWindow()
{
}

void MainWindow::testSlot()
{

}

but I still receive:
QObject::connect: No such slot MainWindow::"testSlot()" in ../connections/MainWindow.cpp:8
false

Do you have any ideas?

Pradeep Kumar

Hi,

@poor_robert , as told by @artwaw change the connect statement , u cannot
provide the function name in quotes.

Both signal and slot function signature has to match.

Thanks,

Pradeep Kumar

result = connect(this, SIGNAL(testSignal()), this, SLOT(testSlot()));

replace the above line and check.

Thanks,

artwaw

@poor_robert said in Connecting to slot by string name:

of course you're right, but in this case I want to know how to connect with slot name in parenthesis so SLOT("testSlot()")); is exactly what I want to try.

Of course I may be wrong and I would welcome an opinion from someone more advanced in the subject but according to my knowledge this will not work at all.

jsulm

@poor_robert said in Connecting to slot by string name:

I want to know how to connect with slot name in parenthesis so SLOT("testSlot()"));

Why? Why do you want to use "?

mrjj

Hi
the SLOT macro converts the function name to a string and hence using a string will not be converted correctly.

# define SLOT(a)     qFlagLocation("1"#a QLOCATION)

And to add to @jsulm , why you want as string anyway ??

poor_robert

Hello @jsulm and @mrjj

The code given above was just an example. The real reason was to use slot as callback. I have created following method and wanted to do following connection:

void MyClass::setCallback(QObject * obj, const char* slotName)
{
    connect(m_member, SIGNAL(updated()), obj, SLOT(slotName));
}

in my implementation obj is class derived from the QObject. I have solved the problem with help of std::function used as callbacks.
Do you know how to solve this in Qt way?

BjornW

I do not know if you can make that work; I doubt it.

Regardless, I think it is a bad idea :). How do you intend to use this? Why? If you retrace your steps a bit and explain what you are doing you may get a good suggestion out of this, I think!

m.sue

@poor_robert said in Connecting to slot by string name:

Just use the SLOT at the place where you call the function:

void MyClass::setCallback(QObject * obj, const char* slotName)
{
    connect(m_member, SIGNAL(updated()), obj, slotName);
}

setCallback(myObj,SLOT(myFunction()));

-Michael.

jsulm

@poor_robert Just pass SLOT(mySlot()) to setCallback :-)

void MyClass::setCallback(QObject * obj, const char* slotStr)
{
    connect(m_member, SIGNAL(updated()), obj, slotStr);
}

setCallback(obj, SLOT(mySlot()));

jsulm

@m.sue You were faster :-)

m.sue

Hi @jsulm

Just seconds :-)

poor_robert

Hello @jsulm and @m-sue

This did the job :). Thanks for the help!