How to emit Signal from nested QML page to python

Question

在我的 QML/python 应用程序中，我可以从 main.qml 向 python 代码发出信号。但是现在在 main.qml 中，我添加了 StackLayout 以加载另一个 page1.qml。在那个 page1.qml 是按钮，现在我想从这个按钮向 python 发出信号。

我使用此方法从 main.qml 文件向 python 发出信号： 但不知道如何从嵌套的 page1.qml

发出它

main.py

from PySide2.QtCore import QObject, QUrl, Slot, Signal, Qt
from PySide2.QtGui import QGuiApplication
from PySide2.QtQml import QQmlApplicationEngine

class Foo(QObject):
    @Slot(str)
    def test_slot(self, input_string : str):
        print(input_string)

if __name__ == "__main__":
    import os
    import sys

    app = QGuiApplication()
    foo = Foo()
    engine = QQmlApplicationEngine()
    
    #CHANGES: line excluded engine.rootContext().setContextProperty("foo", foo)
    
    qml_file = "main.qml"
    current_dir = os.path.dirname(os.path.realpath(__file__))
    filename = os.path.join(current_dir, qml_file)
    engine.load(QUrl.fromLocalFile(filename))
    if not engine.rootObjects():
        sys.exit(-1)
    
    #CHANGES: connect QML signal to Python slot
    engine.rootObjects()[0].test_signal.connect(foo.test_slot, type=Qt.ConnectionType.QueuedConnection)
    
    sys.exit(app.exec_())

main.qml

import QtQuick 2.13
import QtQuick.Controls 2.13

ApplicationWindow {
    visible: true
    
    //CHANGES: declare signal
    signal test_signal(string input_string)

    Button {
        anchors.centerIn: parent
        text: "Example"

        //CHANGES: emit signal
        onClicked: test_signal("Test string")
    }
}

https://stackoverflow.com/a/69595659/5166312

非常感谢。

Answer 1

1. 为嵌套页面添加

   objectName

   字符串属性（如果它们在单独的文件中，则包括大小写）：

   objectName: "page1_objname"
   

2. 从 Python（或 C++）后端访问嵌套页面

   qmlpage1 = engine.rootObjects()[0].findChild(QObject, "page1_objname")
   

3. 像往常一样在 Python 或 C++ 后端连接插槽和信号（您的问题或我的回答中已经有代码https://stackoverflow.com/a/69595659/5166312）。

   qmlpage1.page1_signal.connect(
      test_object.test_slot3,
      type=Qt.ConnectionType.QueuedConnection)
   

我在 https://github.com/Ornstein89/pyside6-qml-slotsignal 上的测试示例中包含 StackLayout、两个嵌套页面、3 个信号和 3 个插槽的整个项目

main.py

# This Python file uses the following encoding: utf-8
import sys
from pathlib import Path

from PySide6.QtCore import QObject, QUrl, Slot, Signal, Qt
from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine

class TestClass(QObject):
    '''
    Object - slot-owner and signal-acceptor
    '''
    @Slot(str)
    def test_slot1(self, input_string : str):
        print(input_string)
    @Slot(str)
    def test_slot2(self, input_string : str):
        print(input_string)
    @Slot(str)
    def test_slot3(self, input_string : str):
        print(input_string)

if __name__ == "__main__":
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    test_object = TestClass()
    qml_file = Path(__file__).resolve().parent / "main.qml"
    engine.load(qml_file)
    if not engine.rootObjects():
        sys.exit(-1)

    # !!! connect ApplicationWindow.mainapp_signal() to test_object.test_slot1
    engine.rootObjects()[0]\
        .mainapp_signal.connect(
            test_object.test_slot1,
            type=Qt.ConnectionType.QueuedConnection)

    # !!! access nested page1 from python backend
    qmlpage1 = engine.rootObjects()[0].findChild(QObject, "page1_objname")

    # !!! and connect MyPage1.page1_signal() to test_object.test_slot2
    qmlpage1.page1_signal.connect(
            test_object.test_slot2,
            type=Qt.ConnectionType.QueuedConnection)

    # !!! access nested page2 from python backend
    qmlpage2 = engine.rootObjects()[0].findChild(QObject, "page2_objname")

    # !!! and connect MyPage2.page2_signal() to test_object.test_slot3
    qmlpage2.page2_signal.connect(
            test_object.test_slot3,
            type=Qt.ConnectionType.QueuedConnection)

    sys.exit(app.exec())

main.qml

import QtQuick
import QtQuick.Window
import QtQuick.Controls
import QtQuick.Layouts

ApplicationWindow {
    width: 480
    height: 640
    visible: true
    title: qsTr("Example for Stackoverflow")

    // !!! singal №1 in root QML Object - most easy to connect in main.py
    signal mainapp_signal(string input_string)

    StackLayout {
        id : stacklayout
        anchors.fill: parent
        MyPage1 {
            id: page1
        }
        MyPage2 {
            id: page2
        }
    }
}

MyPage1.qml

import QtQuick
import QtQuick.Window
import QtQuick.Controls
import QtQuick.Layouts

Page{
    id: page1

    // !!! singal №2 in nested QML Object
    signal page1_signal(string input_string)

    // !!! important - this name is used
    // to access page1 from C++ or Python backend
    objectName: "page1_objname"

    Button{
        text: "Go to page 2"
        anchors.centerIn: parent
        onClicked: {
            stacklayout.currentIndex = 1
            // call root object signal from nested object
            mainapp_signal("mainapp_signal() from page1");
            // call nested object signal from same object
            page1_signal("page1_signal() from page1");
            // call another nested object signal
            page2.page2_signal("page2_signal() from page1");
        }
    }
}

MyPage2.qml

import QtQuick
import QtQuick.Window
import QtQuick.Controls
import QtQuick.Layouts

Page{
    id: page2

    // !!! singal №3 in nested QML Object
    signal page2_signal(string input_string)

    // !!! important - this name is used
    // to access page2 from C++ or Python backend
    objectName: "page2_objname"

    Button{
        text: "Go to page 1"
        anchors.centerIn: parent
        onClicked: {
            stacklayout.currentIndex = 0
        }
    }
}

Answer 2

您可以添加一个

Conections

元素来使用加载组件的信号。
在此处查看文档.

此外，您可以为您的

page1.qml

项目声明一个组件并使用

sourceComponent

的

Loader

属性。通过这种方式，您可以在组件内部使用信号来调用外部方法。在此处查看文档.

Answer 3

我是新手，想做一个简单的应用。我遵循了您的代码，一切都对我有用。但我无法弄清楚如何获得价值 - （input_string）。继续节目。

你能帮帮我吗？

谢谢