How to bind buttons in Qt Quick to Python PyQt 5

Question

How can bind the buttons I create in a .qml script to python PyQt5 code?

example: python:

import sys
from PyQt5.QtCore import QObject, QUrl, Qt
from PyQt5.QtWidgets import QApplication
from PyQt5.QtQml import QQmlApplicationEngine

if __name__ == "__main__":
  app = QApplication(sys.argv)
  engine = QQmlApplicationEngine()
  ctx = engine.rootContext()
  ctx.setContextProperty("main", engine)

  engine.load('test.qml')

  win = engine.rootObjects()[0]
  win.show()
  sys.exit(app.exec_())

qml:

import QtQuick 2.2
import QtQuick.Window 2.1
import QtQuick.Controls 1.2
import QtQuick.Dialogs 1.1

ApplicationWindow {
 title: qsTr("Test Invoke")

 width: 200
 height: 100

 Button{
  y : 70
  text : "About"
  onClicked: {
   print('Hello')
  }

 }
}

How can I do something with Python when the button is clicked? Also: Does anyone has a good resource of examples or doc. about pyqt + qml (qt quick)?

Answer 1

If you name the button, you can connect to its onClick signal, or to a custom signal that it emits in onClicked. Example:

ApplicationWindow {
 title: qsTr("Test Invoke")
 width: 200
 height: 100

 Button {
  signal messageRequired
  objectName: "myButton"
  y : 70
  text : "About"
  onClicked: messageRequired()

 }
}

Note the signal in Button and the objectName property. Then the Python code just before exec could be for example:

def myFunction():
    print 'handler called'

button = win.findChild(QObject, "myButton")
button.messageRequired.connect(myFunction)
button.clicked.connect(myFunction) # works too

Note that in the Button above, onClicked just emits the messageRequired signal, so it is better to drop the custom signal and connect to clicked directly. Both onClicked() and any slots connected to clicked will get called when you click button.

Answer 2

There is another solution which uses a Python model (QObject) in QML.

Python

engine = QQmlApplicationEngine()
engine.load("main.qml")

class Greeter(QObject):
    @pyqtSlot(str)
    def sayHello(self, name):
        print("Hello, " + name)

ctx = engine.rootContext()
ctx.setContextProperty("greeter", Greeter())

QML

Button {
    onClicked: {
        greeter.sayHello("Alice")
    }
}

Ref.

1. https://wiki.qt.io/Qt_for_Python/Connecting_QML_Signals