setContextProperty() 不会在 qml 文件中创建类实例 [英] setContextProperty() doesn't create the class instance inside the qml file

问题描述

main.py 文件显示一个选项卡小部件.在每个选项卡上我加载了一个特定的 qml 文件，但为了这个问题，我将只考虑一个 qml 文件和一个选项卡:

The main.py file displays a Tab Widget. On each Tab I loaded a speciffic qml file but for the sake of this question I will consider only one qml file and one single tab:

import sys, os, math
import numpy as np
from PyQt5 import *

class Tab(QFrame):
    def __init__(self):
        super().__init__()
        self.setGeometry(600, 600, 600, 600)
        self.setWindowTitle("PyQt5 Tab Widget")
       
        vbox = QVBoxLayout()
        tabWidget = QTabWidget()

        tabWidget.addTab(Example01(), "Ex1")
        
        vbox.addWidget(tabWidget)
        self.setLayout(vbox)

class GG(QObject):
    polygonsChanged = pyqtSignal()

    def __init__(self, parent=None):
        super().__init__(parent)
        self._polygons = []
    def get_polygons(self):
        return self._polygons

    def set_polygons(self, polygons):
        self._polygons = polygons
        self.polygonsChanged.emit()

    polygons = pyqtProperty(
        "QVariant", fget=get_polygons, fset=set_polygons,
        notify=polygonsChanged
    )


class Example01(QWidget):

    def __init__(self):
        super().__init__()
        vbox = QVBoxLayout(self)
        vbox.setContentsMargins(0, 0, 0, 0)


        numpy_arrays = np.array(
            [[[100, 100], [150, 200], [50, 300]],
             [[50, 60], [160, 10], [400, 0]]]
        )

        polygons = []
        for ps in numpy_arrays:
            polygon = []
            for p in ps:
                e = QPointF(*p)
                polygon.append(e)
            polygons.append(polygon)

        gg = GG()
        gg.polygons = polygons
        print(gg.polygons)

        ROOT_DIR = os.path.realpath(os.path.dirname(sys.argv[0]))
        # print(ROOT_DIR)

        qml = os.path.join(ROOT_DIR, "QML Files", "Demo01.qml")

        view = QQuickWidget()

        view.setSource(QUrl.fromLocalFile(qml))

        view.rootContext().setContextProperty("gg", gg)

        view.setResizeMode(QQuickWidget.SizeRootObjectToView)
        # widget = QWidget.createWindowContainer(view)
        # vbox.addWidget(widget)

        vbox.addWidget(view)


if __name__ == "__main__":
    App = QApplication(sys.argv)
    tabDialog = Tab()
    tabDialog.show()
    App.exec()

现在是Demo01.qml文件:

Now the Demo01.qml file:

import QtQuick 2.14
import QtQuick.Window 2.14
import QtGraphicalEffects 1.0


Rectangle {
    id: rect

        visible: true
        anchors.fill: parent

        LinearGradient {
                anchors.fill: parent
                //setting gradient at 45 degrees
                start: Qt.point(rect.width, 0)
                end: Qt.point(0, rect.height)
                gradient: Gradient {
                    GradientStop { position: 0.0; color: "#ee9d9d" }
                    GradientStop { position: 1.0; color: "#950707" }
                }
            }

        Canvas {
            id: drawingCanvas
            anchors.fill: parent
            onPaint: {
                var ctx = getContext("2d")
                ctx.lineWidth = 5;
                ctx.strokeStyle = "red"
                console.log(gg)
                for(var i in gg.polygons){
                    var polygon = gg.polygons[i]
                    ctx.beginPath()
                    for(var j in polygon){
                        var p = polygon[j]
                        if(j === 0)
                            ctx.moveTo(p.x, p.y)
                        else
                            ctx.lineTo(p.x, p.y)
                    }
                    ctx.closePath()
                    ctx.stroke()
                }
            }
           
        }
       
       Connections{
            target: gg
            function onPolygonsChanged(){ drawingCanvas.requestPaint()}
        }
       
    }

问题是没有实例化qml文件里面的gg，声称gg对象为空.所以不会在我的画布上画任何东西.我尝试使用 QQuickWidget 和 QQuickView 并得到相同的空结果.如您所见，在 Tab 窗口中加载了 qml 页面，没有任何问题.

The problem is that does not instantiate the gg inside the qml file, claiming that the gg object is null. So does not draw anything on my canvas. I tried with QQuickWidgetand with QQuickView and had the same null result. As you can see the qml page is loaded on the Tab window without any problem.

如果不适用于上述两个元素，如何设置上下文.

How can be set the context thou, if doesn't work with the two mentioned elements.

推荐答案

您的问题有 2 个错误:

Your problem has 2 errors:

• 您必须在加载 .qml 之前设置上下文属性.
• "gg"是一个局部变量，一旦构造函数执行完毕就会被销毁，所以在qml中它将为null，解决方案是延长生命周期，例如通过使其成为类的属性.

class Example01(QWidget):
    def __init__(self):
        super().__init__()
        numpy_arrays = np.array(
            [[[100, 100], [150, 200], [50, 300]], [[50, 60], [160, 10], [400, 0]]]
        )

        polygons = []
        for ps in numpy_arrays:
            polygon = []
            for p in ps:
                e = QPointF(*p)
                polygon.append(e)
            polygons.append(polygon)

        self.gg = GG()
        self.gg.polygons = polygons
        ROOT_DIR = os.path.realpath(os.path.dirname(sys.argv[0]))
        qml = os.path.join(ROOT_DIR, "QML Files", "Demo01.qml")

        view = QQuickWidget()
        view.rootContext().setContextProperty("gg", self.gg)
        view.setSource(QUrl.fromLocalFile(qml))
        view.setResizeMode(QQuickWidget.SizeRootObjectToView)

        vbox = QVBoxLayout(self)
        vbox.setContentsMargins(0, 0, 0, 0)
        vbox.addWidget(view)

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