Qt / PyQt / PySide：重新实现QLineEdit子类的撤销框架时遇到麻烦

问题描述

我创建了一个自定义行编辑小部件，以便我可以将undo / redo命令合并到我的应用程序的一般撤消堆栈中（而不是使用QLineEdit小部件附带的内置撤消/重做工具）。 撤消/重做逻辑非常简单：当行编辑窗口小部件获得焦点时，其内容立即分配给实例变量（self.init_text）; 当行编辑窗口小部件失去焦点时，如果文本内容与self.init_text中存储的文本内容不同，则会创建新的QUndoCommand对象。 undo（）方法会将内容重新设置为self.init_text中的内容，而redo（）方法会将内容重新设置为行编辑窗口小部件失去焦点时捕获的内容。 （在任一方法中，行编辑将再次获得焦点，以便用户明白撤消或重做命令实际受到什么影响。）

它似乎工作正常，但有一个例外：如果用户通过QPushButtons快速循环撤消或重做命令，那么框架就会中断。 我无法描述它，因为我不确定Qt引擎盖下发生了什么，但是，例如，QUndoStack的count（）可能会完全改变。 应用程序继续运行，终端上没有报告错误，但它仍然是一个损坏的撤消堆栈。

我创建了一个小QDialog应用程序，因此您可以尝试重新创建该问题。 （使用Python 2.7.3 / PySide 1.2.1 ...如果你安装了最近的PyQt绑定，我认为除了前两个import语句之外你不需要替换任何东西。）例如，在第一个选项卡的QLineEdit中，如果你输入'hello'，然后选择标签，然后点击返回并键入'world'，然后再次标签，尝试非常快速地点击撤销按钮（向下和超出撤销堆栈的底部）和重做按钮（直到和超出撤销堆栈的顶部）。 对我来说，这足以打破它。

#!/usr/bin/python
#coding=utf-8
from PySide.QtCore import *
from PySide.QtGui import *
import sys

class CustomRightClick(QObject):

    customRightClicked = Signal()

    def __init__(self, parent=None):
        QObject.__init__(self, parent)

    def eventFilter(self, obj, event):
        if event.type() == QEvent.ContextMenu:
            # emit signal so that your widgets can connect a slot to that signal
            self.customRightClicked.emit()
            return True
        else:
            # standard event processing
            return QObject.eventFilter(self, obj, event)

class CommandLineEdit(QUndoCommand):

    def __init__(self, line_edit, init_text, tab_widget, tab_index, description):
        QUndoCommand.__init__(self, description)
        self._line_edit = line_edit
        self._current_text = line_edit.text()
        self._init_text = init_text
        self._tab_widget = tab_widget
        self._tab_index = tab_index

    def undo(self):
        self._line_edit.setText(self._init_text)
        self._tab_widget.setCurrentIndex(self._tab_index)
        self._line_edit.setFocus(Qt.OtherFocusReason)

    def redo(self):
        self._line_edit.setText(self._current_text)
        self._tab_widget.setCurrentIndex(self._tab_index)
        self._line_edit.setFocus(Qt.OtherFocusReason)

class CustomLineEdit(QLineEdit):

    def __init__(self, parent, tab_widget, tab_index):
        super(CustomLineEdit, self).__init__(parent)
        self.parent = parent
        self.tab_widget = tab_widget
        self.tab_index = tab_index
        self.init_text = self.text()
        self.setContextMenuPolicy(Qt.CustomContextMenu)

        undoAction=QAction("Undo", self)
        undoAction.triggered.connect(self.parent.undo_stack.undo)

        self.customContextMenu = QMenu()
        self.customContextMenu.addAction(undoAction)

        custom_clicker = CustomRightClick(self)
        self.installEventFilter(custom_clicker)
        self.right_clicked = False
        custom_clicker.customRightClicked.connect(self.menuShow)

    def menuShow(self):
        self.right_clicked = True   # set self.right_clicked to True so that the focusOutEvent won't push anything to the undo stack as a consequence of right-clicking
        self.customContextMenu.popup(QCursor.pos())
        self.right_clicked = False

    # re-implement focusInEvent() so that it captures as an instance variable the current value of the text *at the time of the focusInEvent(). This will be utilized for the undo stack command push below
    def focusInEvent(self, event):
        self.init_text = self.text()
        QLineEdit.focusInEvent(self, event)

    # re-implement focusOutEvent() so that it pushes the current text to the undo stack.... but only if there was a change!
    def focusOutEvent(self, event):
        if self.text() != self.init_text and not self.right_clicked:
            print "Focus out event. (self.text is %s and init_text is %s). Pushing onto undo stack. (Event reason is %s)" % (self.text(), self.init_text, event.reason())
            command = CommandLineEdit(self, self.init_text, self.tab_widget, self.tab_index, "editing a text box")
            self.parent.undo_stack.push(command)
        QLineEdit.focusOutEvent(self, event)

    def keyPressEvent(self, event):
        if event.key() == Qt.Key_Z:
            if event.modifiers() & Qt.ControlModifier:
                self.parent.undo_stack.undo()
            else:
                QLineEdit.keyPressEvent(self, event)
        elif event.key() == Qt.Key_Y:
            if event.modifiers() & Qt.ControlModifier:
                self.parent.undo_stack.redo()
            else:
                QLineEdit.keyPressEvent(self, event)
        else:
            QLineEdit.keyPressEvent(self, event)

class Form(QDialog):

    def __init__(self, parent=None):
        super(Form, self).__init__(parent)

        self.undo_stack = QUndoStack()

        self.tab_widget = QTabWidget()

        self.line_edit1 = CustomLineEdit(self, self.tab_widget, 0)
        self.line_edit2 = CustomLineEdit(self, self.tab_widget, 1)
        self.undo_counter = QLineEdit()

        tab1widget = QWidget()
        tab1layout = QHBoxLayout()
        tab1layout.addWidget(self.line_edit1)
        tab1widget.setLayout(tab1layout)

        tab2widget = QWidget()
        tab2layout = QHBoxLayout()
        tab2layout.addWidget(self.line_edit2)
        tab2widget.setLayout(tab2layout)

        self.tab_widget.addTab(tab1widget, "Tab 1")
        self.tab_widget.addTab(tab2widget, "Tab 2")

        self.undo_button = QPushButton("Undo")
        self.redo_button = QPushButton("Redo")
        layout = QGridLayout()
        layout.addWidget(self.tab_widget, 0, 0, 1, 2)
        layout.addWidget(self.undo_button, 1, 0)
        layout.addWidget(self.redo_button, 1, 1)
        layout.addWidget(QLabel("Undo Stack Counter"), 2, 0)
        layout.addWidget(self.undo_counter)
        self.setLayout(layout)

        self.undo_button.clicked.connect(self.undo_stack.undo)
        self.redo_button.clicked.connect(self.undo_stack.redo)
        self.undo_stack.indexChanged.connect(self.changeUndoCount)

    def changeUndoCount(self, index):
        self.undo_counter.setText("%s / %s" % (index, self.undo_stack.count()))

app = QApplication(sys.argv)
form = Form()
form.show()
app.exec_()

这是一个Qt错误吗？ 一个PySide错误？ 或者我的重新实施有问题吗？ 任何帮助表示赞赏！

（在审查我的代码时我刚想到我可能会重新实现contextMenuEvent而不是安装事件过滤器，但我认为这与此问题无关。）