Passing another variable to a SLOT in QObject::connect

dangelog

Both statements are invalid.

In short:

connect() wants only the SIGNATURE of the signal/slot (without the return type), not the argument names, nor anything else;
a slot cannot have more arguments than the ones carried by the signal you're connecting to it (where should they come from?);
passing values inside connect() is an error, although it's pretty clear what you'd like to do;
simply use a "proxy" slot that calls the target slot with the arguments, or read the docs about QSignalMapper.

manasij7479

bq. simply use a “proxy” slot that calls the target slot with the arguments....

How do I do that?

Franzk

@
//...
connect(button, SIGNAL(pressed)), SLOT(handleButtonPress()));
//...

void MyClass::handleButtonPress()
{
someLabel->setText("My String");
}@

dangelog

In your (very simple) case, if it's applicable, you can just provide a default argument for the slot. Otherwise, simply create another slot that calls the setText one with the string you want.

Franzk

[quote author="peppe" date="1297240228"]In your (very simple) case, if it's applicable, you can just provide a default argument for the slot. Otherwise, simply create another slot that calls the setText one with the string you want.[/quote]Indeed. With a slot called setText(), providing a default argument can be misleading:

@myLabel->setText();@

What does that do?

Oh well. It's a style issue.

manasij7479

bq. Otherwise, simply create another slot that calls the setText one with the string you want.

Any way without creating whole new classes?

tobias.hunger

"QSignalMapper":http://doc.qt.nokia.com/4.7/qsignalmapper.html might also be an option.

luca

to solve simple problem like yours I use this solution:
@
connect(button1, SIGNAL(clicked()), SLOT(buttonClicked());
connect(button2, SIGNAL(clicked()), SLOT(buttonClicked());
button1->setProperty("name", "button1");
button2->setProperty("name", "button2");
...
...
MyClass::buttonClicked()
{
QPushButton *button = sender();
if(button->property("name").toString() == "button1")
{
.....
.....
}
else if(button->property("name").toString() == "button2")
{
....
....
}
}
@

andre

Luca, that is unsave code.

You don't know what kind of object sender() refers to, or if it is non-0 at all (direct call to buttonClicked()). So, you should at least check that before assuming this. Using a QSignalMapper is the safe way to go, and it still allows other ways to trigger the slot and still work correctly.

Franzk

Safe or not safe, it's arguably not even simpler than the QSignalMapper approach. Likewise, if a slot is going to make (significant) behavioral changes based on the sender(), then it is probably time to review the design anyway.

luca

[quote author="Andre" date="1297288071"]Luca, that is unsave code.

You don't know what kind of object sender() refers to, or if it is non-0 at all (direct call to buttonClicked()). So, you should at least check that before assuming this. Using a QSignalMapper is the safe way to go, and it still allows other ways to trigger the slot and still work correctly.
[/quote]
Yes, I usually check if pointer is a push button with a dynamic_cast:
@
QPushButton button = dynamic_cast<QPushButton>(sender());
if(button==NULL)
{
return;
}
@

Mine is only a fast example...

Franzk

qobject_cast might be more thorough.

MarekR22

Hi there is a tool which do exactly what you need.
See "QSignalMapper":http://doc.trolltech.com/latest/qsignalmapper.html
There is good example how to use it.

goetz

If you're in the same class (or have access to the possible sender objects pointers) you simply can compare pointers:

@
void MyClass::buttonClicked()
{
if(sender() == button1) {
// ....
} else if(sender() == button2) {
// ....
}
}
@