CODEWITHSUNDEEP
qtenums
user672033
user672033

Reputation:

Qt signal with an enum as a parameter

I'm trying to pass an enum as a value to a slot in my program, but I'm having some problems. In my header file I've created the enum:

Q_ENUMS(button_type);
enum button_type {button_back, button_up, button_down, button_ok};
Q_DECLARE_METATYPE(button_type);

And in my .cpp file I'm trying to pass it to a slot:

QObject::connect(buttons->ui.pushButton_back, SIGNAL(clicked()), this, SLOT(input_handler(button_back)));

But when I compile the code I get:

Object::connect: No such slot main_application::input_handler(button_back) in main_application.cpp:44
Object::connect:  (sender name:   'pushButton_back')
Object::connect:  (receiver name: 'main_applicationClass')

It compiles and works fine if I don't pass an argument to input_handler.

I've also read that I should be calling qRegisterMetaType, but I can't seem to get the syntax correct. Here's what I tried:

qRegisterMetaType<button_type>("button_type");

but I get this error:

main_application.h:15:1: error: specializing member ‘::qRegisterMetaType<button_type>’ requires ‘template<>’ syntax

Can anyone shed some light on this for me?

Thanks!

Marlon

Upvotes: 2

Views: 3913

Answers (3)

Sebastian Negraszus
Sebastian Negraszus

Reputation: 12215

Signal and Slot need to have the same parameters. What you want is a QSignalMapper.

edit: Here is an example from an application of mine. It creates 10 menu actions that each are connected to the same slot gotoHistoryPage but each called with a different int value.

m_forwardMenu = new QMenu();
for(int i = 1; i<=10; i++)
{
    QAction* action = m_forwardMenu->addAction(QString("%1").arg(i));
    m_forwardActions.push_back(action);
    m_signalMapper->setMapping(action, i);
    connect(action, SIGNAL(triggered()), m_signalMapper, SLOT(map()));
}
ui.forwardButton->setMenu(m_forwardMenu);
connect(m_signalMapper, SIGNAL(mapped(int)), this, SLOT(gotoHistoryPage(int)));

Upvotes: 3

Lol4t0
Lol4t0

Reputation: 12547

Object::connect: No such slot main_application::input_handler(button_back)

Of course, there is, because signature is main_application::input_handler(button_type), and button_back is a value, not type. And even you make right signature, you will not be able to connect that signal and slot due to their signature mismatch.

Also, you can always use QObject::sender() function to get known, what button was pressed.

Upvotes: 0

Stu Mackellar
Stu Mackellar

Reputation: 11638

You're passing the SLOT() macro a value when it's expecting a type. More fundamentally this doesn't make much sense anyway as what you're struggling to achieve is to pass the slot a constant. Why not just use button_back in the slot function directly?

You can define a slot which takes a button_type value, but then you'd need to connect it to a signal that passes one as a parameter.

What are you actually trying to do?

Upvotes: 1

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