移动项目时，QStandardItem未正确克隆

Question

如下面的代码所示，当您拖放一个项(使用clone()方法从QStandardItem派生出的子类(时，您会得到一个QStandardItem，而不是一个子类。此外，存储在类中或作为setData一部分的数据将丢失。我怀疑这是因为无法"序列化"数据。但我不知道如何"保存"数据或元数据。如何保存QObject？以下代码工作正常，但一旦移动分支节点，分支和分支中的所有节点都将成为QStandardItem的，而不是myItem的，并丢失数据(如果有(。

# -*- coding: utf-8 -*-
"""
Created on Mon Nov  4 09:10:16 2019
Test of Tree view with subclassed QStandardItem and Drag and Drop
enabled.  When you move a parent the parent looses the subclass and thus
the meta - however, it also looses the data:  This is likely because
the data cannot be serialized.  How to fix?
@author: tcarnaha
"""
import sys
from PyQt5 import QtGui, QtWidgets, QtCore

class myData():
def __init__(self, title):
self._title = title
self._stuff = dict()
self._obj = QtCore.QObject()
@property
def obj(self):
return self._obj
@obj.setter
def obj(self, value):
self._obj = value
@property
def title(self):
return self._title
@title.setter
def title(self, value):
self._title = value

class myItem(QtGui.QStandardItem):
def __init__(self, parent=None):
super(myItem, self).__init__(parent)
self._meta = None
@property
def meta(self):
return self._meta
@meta.setter
def meta(self, value):
self._meta = value
def clone(self):
print "My cloning"
old_data = self.data()
print "Old data [{}]".format(old_data)
old_meta = self.meta
obj = myItem()
obj.setData(old_data)
print "New data [{}]".format(obj.data())
obj.meta = old_meta
print "Clone is a ", obj.__class__
return obj
class mainWidget(QtWidgets.QMainWindow):
def __init__(self):
super(mainWidget, self).__init__()
self.model = QtGui.QStandardItemModel()
self.model.setItemPrototype(myItem())
self.view = QtWidgets.QTreeView()
self.view.setContextMenuPolicy(QtCore.Qt.CustomContextMenu)
self.view.customContextMenuRequested.connect(self.list_click)
self.view.setDragDropMode(QtWidgets.QAbstractItemView.InternalMove)
self.view.setDefaultDropAction(QtCore.Qt.MoveAction)
self.view.setDragDropOverwriteMode(False)
self.view.setAcceptDrops(True)
self.view.setDropIndicatorShown(True)
self.view.setDragEnabled(True)
self.view.setModel(self.model)
dataA = myData('A thing')
parentA = myItem()
parentA.setText('A')
parentA.setDragEnabled(True)
parentA.setDropEnabled(True)
parentA.setData(dataA)
parentA.meta = QtCore.QObject()
childa = myItem()
childa.setText('a')
childb = myItem()
childb.setText('b')
childc = myItem()
childc.setText('c')
parentA.appendRows([childa, childb, childc])
dataB = myData('B thing')
parentB = myItem()
parentB.setText('B')
parentB.setDragEnabled(True)
parentB.setDropEnabled(True)
parentB.setData(dataB)
parentB.meta = QtCore.QObject()
childd = myItem()
childd.setText('d')
childe = myItem()
childe.setText('e')
childf = myItem()
childf.setText('f')
parentB.appendRows([childd, childe, childf])
self.model.appendRow(parentA)
self.model.appendRow(parentB)
classAct = QtWidgets.QAction('Class', self)
classAct.triggered.connect(self.classIs)
dataAct = QtWidgets.QAction('Data', self)
dataAct.triggered.connect(self.dataIs)
metaAct = QtWidgets.QAction('Meta', self)
metaAct.triggered.connect(self.metaIs)
self.menu = QtWidgets.QMenu("Item info")
self.menu.addAction(classAct)
self.menu.addAction(dataAct)
self.menu.addAction(metaAct)
self.setCentralWidget(self.view)
@QtCore.pyqtSlot(QtCore.QPoint)
def list_click(self, position):
self.menu.popup(self.view.viewport().mapToGlobal(position))
def classIs(self):
selected_indexes = self.view.selectedIndexes()
for index in selected_indexes:
item = self.model.itemFromIndex(index)
print "Item {} Class {} ".format(item.text(), item.__class__())
def dataIs(self):
selected_indexes = self.view.selectedIndexes()
for index in selected_indexes:
item = self.model.itemFromIndex(index)
try:
print "Item {} data {} Object {}".format(item.text(),
item.data().title,
item.data().obj)
except Exception as exc:
print "Data exception ", exc
def metaIs(self):
selected_indexes = self.view.selectedIndexes()
for index in selected_indexes:
item = self.model.itemFromIndex(index)
try:
print "Item {} meta {} ".format(item.text(), item.meta)
except Exception as exc:
print "Meta exception ", exc

if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
main = mainWidget()
main.show()
app.exec_()

Answer 1

这里有几个问题与Qt和PyQt如何序列化对象有关。首先，在克隆QStandardItem时，只复制标志和数据，而忽略其他所有内容(包括动态python属性(。其次，无法直接复制QObject。这是因为它不能被强制转换为QVariant(Qt用于序列化(，也不能被pickle(PyQt用于串行化(。

为了解决第二个问题，我们需要保留对所有QObject实例的单独引用，然后使用间接密钥稍后再次访问它们。可能有很多不同的方法来实现这一点，但这里有一个非常简单的方法来说明基本思想：

objects = {}
class MyObject(QtCore.QObject):
def __init__(self, parent=None):
super(MyObject, self).__init__(parent)
self.setProperty('key', max(objects.keys() or [0]) + 1)
objects[self.property('key')] = self

因此，这会自动将每个实例添加到全局缓存中，并为其提供一个唯一的查找关键字，以便以后可以很容易地找到它。有了这一点，myData类现在需要适应使用MyObject类，以便正确处理酸洗：

class myData():
def __init__(self, title):
self._title = title
self._stuff = dict()
self._obj = MyObject()
def __setstate__(self, state):
self._obj = objects.get(state['obj'])
self._stuff = state['stuff']
self._title = state['title']
def __getstate__(self):
return {
'obj': self._obj and self._obj.property('key'),
'title': self._title,
'stuff': self._stuff,
}

解决第一个问题要简单得多：我们只需要确保任何动态python属性都使用自定义数据角色将其底层值存储在项的数据中。在这种特殊情况下，该值必须是项目的MyObject实例的键，以便可以在拖放操作后检索：

class myItem(QtGui.QStandardItem):
MetaRole = QtCore.Qt.UserRole + 1000
@property
def meta(self):
return objects.get(self.data(myItem.MetaRole))
@meta.setter
def meta(self, value):
self.setData(value.property('key'), myItem.MetaRole)
def clone(self):
print "My cloning"
obj = myItem(self)
print "Clone is a ", obj.__class__
return obj

以下是实现上述所有内容的原始脚本的工作版本。但请记住，您几乎肯定需要对此进行调整，以便与您的真实代码正常工作。这只是一个有效的概念证明，展示了如何处理上述两个问题。

# -*- coding: utf-8 -*-
import sys
from PyQt5 import QtGui, QtWidgets, QtCore
objects = {}
class MyObject(QtCore.QObject):
def __init__(self, parent=None):
super(MyObject, self).__init__(parent)
self.setProperty('key', max(objects.keys() or [0]) + 1)
objects[self.property('key')] = self
class myData():
def __init__(self, title):
self._title = title
self._stuff = dict()
self._obj = MyObject()
def __setstate__(self, state):
self._obj = objects.get(state['obj'])
self._stuff = state['stuff']
self._title = state['title']
def __getstate__(self):
return {
'obj': self._obj.property('key'),
'title': self._title,
'stuff': self._stuff,
}
@property
def obj(self):
return self._obj
@obj.setter
def obj(self, value):
self._obj = value
@property
def title(self):
return self._title
@title.setter
def title(self, value):
self._title = value
class myItem(QtGui.QStandardItem):
MetaRole = QtCore.Qt.UserRole + 1000
@property
def meta(self):
return objects.get(self.data(myItem.MetaRole))
@meta.setter
def meta(self, value):
self.setData(value.property('key'), myItem.MetaRole)
def clone(self):
print "My cloning"
obj = myItem(self)
print "Clone is a ", obj.__class__
return obj
class mainWidget(QtWidgets.QMainWindow):
def __init__(self):
super(mainWidget, self).__init__()
self.model = QtGui.QStandardItemModel()
self.model.setItemPrototype(myItem())
self.view = QtWidgets.QTreeView()
self.view.setContextMenuPolicy(QtCore.Qt.CustomContextMenu)
self.view.customContextMenuRequested.connect(self.list_click)
self.view.setDragDropMode(QtWidgets.QAbstractItemView.InternalMove)
self.view.setDefaultDropAction(QtCore.Qt.MoveAction)
self.view.setDragDropOverwriteMode(False)
self.view.setAcceptDrops(True)
self.view.setDropIndicatorShown(True)
self.view.setDragEnabled(True)
self.view.setModel(self.model)
dataA = myData('A thing')
parentA = myItem()
parentA.setText('A')
parentA.setDragEnabled(True)
parentA.setDropEnabled(True)
parentA.setData(dataA)
parentA.meta = MyObject()
childa = myItem()
childa.setText('a')
childb = myItem()
childb.setText('b')
childc = myItem()
childc.setText('c')
parentA.appendRows([childa, childb, childc])
dataB = myData('B thing')
parentB = myItem()
parentB.setText('B')
parentB.setDragEnabled(True)
parentB.setDropEnabled(True)
parentB.setData(dataB)
parentB.meta = MyObject()
childd = myItem()
childd.setText('d')
childe = myItem()
childe.setText('e')
childf = myItem()
childf.setText('f')
parentB.appendRows([childd, childe, childf])
self.model.appendRow(parentA)
self.model.appendRow(parentB)
classAct = QtWidgets.QAction('Class', self)
classAct.triggered.connect(self.classIs)
dataAct = QtWidgets.QAction('Data', self)
dataAct.triggered.connect(self.dataIs)
metaAct = QtWidgets.QAction('Meta', self)
metaAct.triggered.connect(self.metaIs)
self.menu = QtWidgets.QMenu("Item info")
self.menu.addAction(classAct)
self.menu.addAction(dataAct)
self.menu.addAction(metaAct)
self.setCentralWidget(self.view)
@QtCore.pyqtSlot(QtCore.QPoint)
def list_click(self, position):
self.menu.popup(self.view.viewport().mapToGlobal(position))
def classIs(self):
selected_indexes = self.view.selectedIndexes()
for index in selected_indexes:
item = self.model.itemFromIndex(index)
print "Item {} Class {} ".format(item.text(), item.__class__())
def dataIs(self):
selected_indexes = self.view.selectedIndexes()
for index in selected_indexes:
item = self.model.itemFromIndex(index)
try:
print "Item {} data {} Object {}".format(item.text(),
item.data().title,
item.data().obj)
except Exception as exc:
print "Data exception ", exc
def metaIs(self):
selected_indexes = self.view.selectedIndexes()
for index in selected_indexes:
item = self.model.itemFromIndex(index)
try:
print "Item {} meta {} ".format(item.text(), item.meta)
except Exception as exc:
print "Meta exception ", exc

if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
main = mainWidget()
main.show()
app.exec_()

Answer 2

您不是在克隆您的类，而是一个正常的QStandardItem:

obj = super(myItem, self).clone()

这实际上意味着"调用基类的clone()方法">
当从单个类进行子类化时，super()的行为与调用以子类实例为第一个参数的类方法完全相同，因此在这种情况下，它的行为非常糟糕：

obj = QtGui.QStandardItem.clone(self)

super()最常见的优点是简单性和可维护性(如果您更改要继承的基类，则只需在子类声明中进行更改(；除此之外，它最重要的好处来自多重继承，即当您从继承多个基类时，但由于这在PyQt中是罕见的情况，因此情况并非如此；此外，多继承是不可能与一个以上的Qt类。

如setItemPrototype()(强调矿(中所述：

要提供您自己的原型，子类QStandardItem，请重新实现QStandardItem:：clone((，并将原型设置为自定义类。

实际上，clone()所做的是使用QStandardItem(other)构造函数，该构造函数创建其他项的副本。

因此，您可以通过以下操作获得正确的克隆：

def clone(self):
obj = myItem(self)
obj.setData(self.data())
obj.meta = self.meta
return obj