PySide: Returning a value from a slot

Question

The Pyside documentation states that slots can have return values, but I have yet to figure out how make it do so.

I couldn't find any usable code samples on this, so I've added a decorator as the docs suggest:

def testSlot(self):
    print('testSlot called')
    return 'RETURN VALUE RETURN VALUE RETURN VALUE'

And I'm trying to capture the return value like this:

ret = foo.testSignal.emit()

But it's not working. My test code, which you can find here , also crashes with this error output. Help is appreciated!

Edit: I've removed the decorator, which solves the crashing issue, but it still doesn't return the value I want it to return.

Running the script as is give me this:

foo.testSignal.emit()
testSlot called
True

Answer 1

I'm afraid what you think is not possible. Signals and slots are loosely coupled together, so emitting a signal does not directly call a slot, and therefore cannot retrieve "its" return value .

This might be clearer if you think about this:

You can connect 2 different slots (of eg 2 different classes), which return different values, to one signal . Which of the two return values are supposed to reach the variable you try to assign?

What you probably mean is this : This is something completely different, and allows return values via "invoking" the method over the MetaObject system by "name".

Answer 2

也许您可以将想要从 testSlot 函数返回的任何内容“注入”到发出信号的类的属性中

Answer 3

This question is old but it seems now there is a way to do return a value from a slot call (call python/PySide2 slot from QML ):

Python Side (Slot) :

# Main.py
# add imports ... 

# Class to set the context on QML frontend
class PythonQObject(QObject):

  @Slot(result=int)
  def returnSomeInt(self):
    return 456


# Set the context etc, on main
if __name__ == "__main__":
  pyQObject = PythonQObject()
  app = QApplication(sys.argv)
  engine = QQmlApplicationEngine()
  engine.rootContext().setContextProperty("backend", pyQObject )
  engine.load(os.path.join(basedir, 'main.qml'))
  sys.exit(app.exec_())
  

QML Side:

/* main.qml */
import QtQuick 2.15
import QtQuick.Window 2.15
import QtQuick.Controls 2.15

Window {
    id: mainWindow

    Component.onCompleted: {
        /* Get the return value from slot here */
        let value = backend.returnSomeInt()
    }

}