关于QML和PySide2的几个问题

Question

我有以下情况，我想使用几个Qml："welcome.Qml"、"create.Qml"、"dashboard.Qml

在哪些情况下使用QQuickview或QqmlApplicationEngine。？

我使用"QQmlAplicatiobEngine"，并用findChild在对象中搜索以获得信号，并处理逻辑。如果信号完成了一个条件，我使用engine.load加载另一个QML。

python:

class guiBackend(QObject):
def __init__(self):
self.engine = QQmlApplicationEngine()
self.context = self.engine.rootContext()
self.context.setContextProperty("main", self.engine)
self.welcome()
def welcome(self):
self.engine.load("welcome.qml")
self.engine.rootObjects()[0].show()
ob = self.engine.rootObjects()[0]
next = ob.findChild(QObject, "timer")
print(dir(next))
if  path.exists('data.some'):
next.change.connect(self.open_account)
else:
next.change.connect(self.create_account)
def create(self):
self.engine.rootObjects()[0].close()
self.engine.load("create.qml")
self.engine.rootObjects()[1].show()
add = ob.findChild(QObject, "addWallet")
recovery = ob.findChild(QObject, "recovery")
add.change.connect(self.add_account)
recovery.change.connect(self.recovery)
#self.open_account load dashboard.qml and self.account load form.qml
if __name__ == "__main__":
app = QGuiApplication(sys.argv)
gui = guiBackend()
sys.exit(app.exec_())

Qml:

ApplicationWindow {
id: welcome
width: 650; height: 390
opacity: 1
visible: true
minimumHeight: 232
minimumWidth:226
title: "open account"
flags: Qt.SplashScreen
Item {
id: element
x: 9
y: 88
width: 560
height: 300
anchors.horizontalCenter: parent.horizontalCenter
anchors.verticalCenter: parent.verticalCenter
Timer {
signal change
objectName: "timer"
interval: 5000; running: true; repeat: false
onTriggered: change()
}
Image {
id: image
x: 130
y: 60
width: 342
height: 188
anchors.verticalCenterOffset: -56
anchors.horizontalCenterOffset: 0
anchors.verticalCenter: parent.verticalCenter
anchors.horizontalCenter: parent.horizontalCenter
source: "neirons_logo.png"
fillMode: Image.PreserveAspectFit
}
AnimatedImage {
id: animatedImage
x: 236
y: 200
width: 100
height: 100
source: "loading.gif"
}
}
}

create.qml:

ApplicationWindow {
id: create
width: 210; height: 210
Rectangle {
id: rectangle
x: 70
y: 132
width: 200
height: 200
color: "#72ded8"
anchors.verticalCenterOffset: 0
anchors.horizontalCenterOffset: 0
anchors.horizontalCenter: parent.horizontalCenter
anchors.verticalCenter: parent.verticalCenter
ColumnLayout {
x: 60
y: 73
width: 109
height: 128
anchors.verticalCenter: parent.verticalCenter
anchors.horizontalCenter: parent.horizontalCenter
TextInput {
id: nameAccount
objectName: textAccount
text: qsTr("nameAccount")
Layout.fillWidth: true
Layout.alignment: Qt.AlignHCenter | Qt.AlignTop
Layout.preferredHeight: 20
Layout.preferredWidth: 80
verticalAlignment: Text.AlignVCenter
font.pixelSize: 12
}
TextInput {
id: nameAccount
objectName: textAccount
text: qsTr("Name Account")
Layout.fillWidth: true
Layout.alignment: Qt.AlignHCenter | Qt.AlignTop
Layout.preferredHeight: 20
Layout.preferredWidth: 80
font.pixelSize: 12
}
}
Button {
signal addinfo
id: submitNameAccount
objectName: submit
x: 50
y: 134
width: 81
height: 23
text: qsTr("Add")
font.bold: true
font.pointSize: 12
anchors.horizontalCenter: parent.horizontalCenter
onClicked: addinfo()
}

}

使用QQuickview或QQmlAplicationEngine效果更好。

Answer 1

根据OP提供的内容，我将指出以下方面：

• 什么时候应该使用QQmlAplicationEngine或QQuickview？QQmlAplicationEngine还是QQuickview更好

  其中一个或另一个的使用取决于QML的根元素，如果根是Window或ApplicationWindow，则必须使用QQmlAplicationEngine，如果它是Item或其衍生物，则可以使用QQuickView。因此，对于上面的一个并不比另一个好。如果我用根窗口加载QML或用QQuickView加载ApplicationWindow会发生什么？然后它将显示两个窗口：一个来自QQuickView，另一个来自Window或ApplicationWindow。如果我用QQmlApplicationEngine加载一个带有Item的QML怎么办？好吧，你需要把它放在一个窗口内，如文件所示：

  与QQuickView不同，QQmlApplicationEngine不会自动创建根窗口。如果您正在使用Qt Quick中的视觉项目，则需要将它们放置在Window中。

• 不要从python/C++访问QML元素

  QML有自己对变量的处理，所以您可以随时删除或创建它，但还没有确定，所以访问这些对象可能很危险，因为它们可能没有分配内存。正确的做法是反其道而行之，将QObject导出到QML并在QML中建立连接。

---

我们将把上面的概念应用到OP提供的代码中(我已经纠正了一些类型(。

• 首先，由于根是ApplicationWindow，因此应该使用QQmlApplicationEngine。

• 您可以使用setContextProperty将后端导出到QML，然后直接调用插槽，而不是在每个元素中创建"更改"信号。使用rootObjects((获取对象是危险的，因为有异步加载的qml，请使用objectCreated信号。

main.py

import os
from PyQt5 import QtCore, QtGui, QtQml
CURRENT_DIR = os.path.dirname(os.path.realpath(__file__))

class Backend(QtCore.QObject):
def __init__(self, parent=None):
super().__init__(parent)
self._engine = QtQml.QQmlApplicationEngine()
self._welcome = None
self._wallet = None
self.engine.objectCreated.connect(self.on_object_created)
self.engine.rootContext().setContextProperty("backend", self)
self.load_welcome()
@property
def engine(self):
return self._engine
@property
def welcome(self):
return self._welcome
@property
def wallet(self):
return self._wallet
@staticmethod
def create_url(qml):
return QtCore.QUrl.fromLocalFile(os.path.join(CURRENT_DIR, qml))
def load_welcome(self):
self.engine.load(self.create_url("welcome.qml"))
@QtCore.pyqtSlot(QtCore.QObject, QtCore.QUrl)
def on_object_created(self, obj, url):
if url == self.create_url("welcome.qml"):
self._welcome = obj
elif url == self.create_url("wallet.qml"):
self._wallet = obj
@QtCore.pyqtSlot()
def create_wallet(self):
self.welcome.close()
self.engine.load(self.create_url("wallet.qml"))
@QtCore.pyqtSlot()
def add_info(self):
print("add_info")

if __name__ == "__main__":
import sys
app = QtGui.QGuiApplication(sys.argv)
backend = Backend()
sys.exit(app.exec_())

欢迎。qml

import QtQuick 2.14
import QtQuick.Controls 2.14
ApplicationWindow {
id: root
width: 650; height: 390
opacity: 1
visible: true
minimumHeight: 232
minimumWidth:226
title: "open account"
flags: Qt.SplashScreen
Item {
id: element
x: 9
y: 88
width: 560
height: 300
anchors.horizontalCenter: parent.horizontalCenter
anchors.verticalCenter: parent.verticalCenter
Timer {
interval: 5000; running: true; repeat: false
onTriggered: backend.create_wallet()
}
Image {
id: image
x: 130
y: 60
width: 342
height: 188
anchors.verticalCenterOffset: -56
anchors.horizontalCenterOffset: 0
anchors.verticalCenter: parent.verticalCenter
anchors.horizontalCenter: parent.horizontalCenter
source: "neirons_logo.png"
fillMode: Image.PreserveAspectFit
}
AnimatedImage {
id: animatedImage
x: 236
y: 200
width: 100
height: 100
source: "loading.gif"
}
}
}

钱包.qml

import QtQuick 2.14
import QtQuick.Controls 2.14
import QtQuick.Layouts 1.14

ApplicationWindow {
id: root
visible: true
width: 210; height: 210
Rectangle {
id: rectangle
x: 70
y: 132
width: 200
height: 200
color: "#72ded8"
anchors.verticalCenterOffset: 0
anchors.horizontalCenterOffset: 0
anchors.horizontalCenter: parent.horizontalCenter
anchors.verticalCenter: parent.verticalCenter
ColumnLayout {
x: 60
y: 73
width: 109
height: 128
anchors.verticalCenter: parent.verticalCenter
anchors.horizontalCenter: parent.horizontalCenter
TextInput {
id: nameAccount1
text: qsTr("nameAccount")
Layout.fillWidth: true
Layout.alignment: Qt.AlignHCenter | Qt.AlignTop
Layout.preferredHeight: 20
Layout.preferredWidth: 80
verticalAlignment: Text.AlignVCenter
font.pixelSize: 12
}
TextInput {
id: nameAccount2
text: qsTr("Name Account")
Layout.fillWidth: true
Layout.alignment: Qt.AlignHCenter | Qt.AlignTop
Layout.preferredHeight: 20
Layout.preferredWidth: 80
font.pixelSize: 12
}
}
Button {
id: submitNameAccount
x: 50
y: 134
width: 81
height: 23
text: qsTr("Add")
font.bold: true
font.pointSize: 12
anchors.horizontalCenter: parent.horizontalCenter
onClicked: backend.add_info()
}
}
}