python - 移动项目时，QStandardItem 无法正确克隆

Question

如以下代码所示，当您拖放一个项目(使用 clone() 方法从 QStandardItem 子类化)时，您将获得一个 QStandardItem 而不是子类。此外，存储在类中或作为 setData 一部分的数据会丢失。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。如何保留QObject？下面的代码工作正常，但是一旦移动分支节点，分支和分支中的所有节点都会变成 QStandardItem 的而不是 myItem 并丢失数据(如果他们有任何)。

# -*- 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

这里有几个与 Qt 和 PyQt 如何序列化对象相关的问题。首先，当克隆 QStandardItem 时，仅复制标志和数据 - 其他所有内容都将被忽略(包括动态 python 属性)。其次，没有办法直接复制QObject。这是因为它无法转换为 QVariant(Qt 用于序列化)并且无法进行 pickle(PyQt 用于序列化)。

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，然后使用间接键稍后再次访问它们。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，并为其提供唯一的查找键，以便以后可以轻松找到它。完成此操作后，现在需要调整 myData 类以使用 MyObject 类，以便 pickling is handled correctly :

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 属性使用自定义数据角色将其基础值存储在项目的数据中。在这种特殊情况下，该值必须是项目的 MyObject 实例的键，以便在拖放操作后可以检索它:

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

下面是原始脚本的工作版本，它实现了上述所有内容。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验证，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_()