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我正在尝试使用 QML 和 PyQt5
Python 代码更改存储在文件夹中的按钮（GPIO PIN）的图像：

from gpiozero import Button
from signal import pause

from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtQml import *
import os, time, sys


def btn_pressed():
    global r
    return lambda: r.setProperty("source", "/home/pi/Desktop/example/sample/img/img1.jpg")

button1 = Button(20)        
myApp = QGuiApplication([])
myEngine = QQmlApplicationEngine()
directory = os.path.dirname(os.path.abspath(__file__))
myEngine.load(QUrl.fromLocalFile(os.path.join(directory, 'simple1.qml')))
if not myEngine.rootObjects():
    print("root object not found")

r = myEngine.rootObjects()[0].findChild(QObject, "DisplayImage")
dir(r)
print("Main Thead id ",myApp.thread())
updateUI = UpdateUI()

button1.when_pressed = btn_pressed()   
myEngine.quit.connect(myApp.quit)
sys.exit(myApp.exec_())

QML：

import QtQuick 2.10
import QtQuick.Controls 1.6
import QtQuick.Window 2.2

ApplicationWindow {
    id : main
    title: qsTr("Test")
    width: 640
    height: 480
    visible: true

    Rectangle{
        width: parent.width
        height: parent.height

        Image {
            id: img
            source: ""
            width : main.width;
            fillMode : Image.PreserveAspectFit
            objectName: "DisplayImage"
        }
    }
}

当我在树莓派 4 中按下连接到 GPIO 20 的按钮时，我收到以下错误消息。

QObject: Cannot create children for a parent that is in a different thread. 
(Parent is QQmlApplicationEngine(0x10f5ba0), parent's thread is QThread(0xf6f7c0), current thread is QThread(0xa98007c8)
Updates can only be scheduled from GUI thread or from QQuickItem::updatePaintNode()

我还尝试使用更改图像源属性的方法创建类，然后在按下 PushButton 时调用相同的方法（通过类对象），但它显示相同的错误消息

有没有办法Source在 QML 中设置图像的属性 - 从 Python 中的父线程。

在 Winforms 中，我们可以通过使用Delegates.

我们可以用Signal and SlotPyQt5 解决这个问题吗？

4

1 回答 1

1

使用线程来监控 gpio 以免阻塞主 GUI，因此相关函数 when_pressed 将在该线程中执行，但 Qt 禁止从另一个线程更新 GUI 元素，例如图像。

解决方案是创建一个 QObject，它在与 when_pressed 关联的方法中发出信号，因为信号是线程安全的。

另一方面，从 C++/Python 修改 QML 元素并不好，最好将 QObject 导出到 QML 并在该范围内建立连接。

import os
import sys

from gpiozero import Button

from PyQt5.QtCore import pyqtSignal, QObject, QUrl
from PyQt5.QtGui import QGuiApplication
from PyQt5.QtQml import QQmlApplicationEngine


class ButtonManager(QObject):
    pressed = pyqtSignal()

    def __init__(self, parent=None):
        super().__init__(parent)
        self._button = Button(20)
        self._button.when_pressed = self._on_when_pressed

    def _on_when_pressed(self):
        self.pressed.emit()


if __name__ == "__main__":
    app = QGuiApplication(sys.argv)
    button_manager = ButtonManager()
    engine = QQmlApplicationEngine()
    engine.rootContext().setContextProperty("button_manager", button_manager)
    current_dir = os.path.dirname(os.path.abspath(__file__))
    engine.load(QUrl.fromLocalFile(os.path.join(current_dir, "simple1.qml")))
    if not engine.rootObjects():
        print("root object not found")
        sys.exit(-1)
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())

simple1.qml

import QtQuick 2.10
import QtQuick.Controls 1.6
import QtQuick.Window 2.2

ApplicationWindow {
    id : main
    title: qsTr("Test")
    width: 640
    height: 480
    visible: true
    Rectangle{
        anchors.fill: parent
        Image {
            id: img 
            width : main.width
            fillMode : Image.PreserveAspectFit
        }
    }
    Connections{
        target: button_manager
        onPressed: img.source = "/home/pi/Desktop/example/sample/img/img1.jpg"
    }
}
于 2020-01-11T00:46:41.397 回答