在PyQt QTreeWidget中移动节点位置

Question

当用户按下按钮时，我正试图在其父级中向上移动节点。我给孩子们拍了一张快照，对他们重新排序，然后把他们都加回来。然而，最初选择的节点从未被takeChild（）方法删除，所以我最终在父节点中有3个节点，而不是两个。请尝试以下示例，方法是选择类型B节点，然后单击"上移节点"按钮。基本的树代码取自另一个so qq，并在下面引用。

import sys
from PyQt4 import QtCore, QtGui
from PyQt4.QtCore import Qt
#see http://stackoverflow.com/questions/12737721/developing-pyqt4-tree-widget/13563375#13563375
class Window(QtGui.QWidget):
    def __init__(self):
        QtGui.QWidget.__init__(self)
        self.treeWidget = QtGui.QTreeWidget()
        self.treeWidget.setHeaderHidden(True)
        self.addItems(self.treeWidget.invisibleRootItem())
        self.treeWidget.itemChanged.connect (self.handleChanged)
        layout = QtGui.QVBoxLayout()
        layout.addWidget(self.treeWidget)
        self.upPushButton = QtGui.QPushButton("Move node up")
        layout.addWidget(self.upPushButton)
        self.setLayout(layout)
        self.connectSlot()
    def addItems(self, parent):
        column = 0
        clients_item = self.addParent(parent, column, 'Clients', 'data Clients')
        vendors_item = self.addParent(parent, column, 'Vendors', 'data Vendors')
        time_period_item = self.addParent(parent, column, 'Time Period', 'data Time Period')
        self.addChild(clients_item, column, 'Type A', 'data Type A')
        self.addChild(clients_item, column, 'Type B', 'data Type B')
        self.addChild(vendors_item, column, 'Mary', 'data Mary')
        self.addChild(vendors_item, column, 'Arnold', 'data Arnold')
        self.addChild(time_period_item, column, 'Init', 'data Init')
        self.addChild(time_period_item, column, 'End', 'data End')
    def addParent(self, parent, column, title, data):
        item = QtGui.QTreeWidgetItem(parent, [title])
        item.setData(column, QtCore.Qt.UserRole, data)
        item.setChildIndicatorPolicy(QtGui.QTreeWidgetItem.ShowIndicator)
        item.setExpanded (True)
        return item
    def addChild(self, parent, column, title, data):
        item = QtGui.QTreeWidgetItem(parent, [title])
        item.setData(column, QtCore.Qt.UserRole, data)
        item.setCheckState (column, QtCore.Qt.Unchecked)
        return item
    def handleChanged(self, item, column):
        if item.checkState(column) == QtCore.Qt.Checked:
            print ("checked", item, item.text(column))
        if item.checkState(column) == QtCore.Qt.Unchecked:
            print ("unchecked", item, item.text(column))
    def upPushButtonClicked(self):
        '''Moves order within parent'''
        selectedTreeItems = self.treeWidget.selectedItems()
        if selectedTreeItems and len(selectedTreeItems) == 1:
            item = selectedTreeItems[0]
            itemData =  item.data(0, Qt.UserRole)
            parent = item.parent()
            #get children
            location = 0
            siblings = []
            if parent.childCount()>1:
                for i in range(parent.childCount()):
                    sibling = parent.child(i)
                    if sibling == item:
                        location = i
                    siblings.append(sibling)
            #switch position
            a, b = siblings.index(parent.child(location-1)), siblings.index(parent.child(location))
            siblings[b], siblings[a] = siblings[a], siblings[b]
            #clear the branch
            for j in range(parent.childCount()): 
                #This runs but the child is not removed when j == childCount-1
                parent.takeChild(j)
            #add all children back
            for node in siblings:
                self.addChild(parent, 0, node.text(0), node.data(0,     Qt.UserRole))            
    def connectSlot(self):
        self.upPushButton.clicked.connect(self.upPushButtonClicked)
if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    window = Window()
    window.show()
    sys.exit(app.exec_())

Answer 1

出现问题的原因是，一旦删除了索引为0的项（第一次迭代时为parent.takechild(j)），那么现在唯一剩下的项就在索引0处。但是下一次迭代尝试删除索引为1的子项，该子项现在不存在！

简而言之，当您修改树视图时（在本例中是通过删除项），用于跟踪树视图中某个位置的任何索引都将变得毫无意义。

您可以通过使用parent.takeChildren()一次删除所有项目或使用for j in range(parent.childCount()-1,-1,-1)向后遍历列表来解决您的特定问题。

请注意，在使用树视图进行其他操作时，应该记住这类问题。您必须仔细考虑更改树视图将如何影响用于访问树视图的任何整数！