在 QComboBox 激活时获取上一个和新选择的项目

Question

在我的程序中，一些组合框 (QComboBox) 用于进行多项设置。有时不仅需要知道用户选择的项目，还需要知道先前在组合框中选择的项目。 好吧，转移新的选择很容易：

self.MyCombobox.activated[str].connect(self.ComboChange)

但是，当索引更改时，我如何不仅将新选择的项目传递给函数，还将前一个项目传递给函数？

我的折衷解决方案是为每个组合框手动设置一个变量，该变量存储最后选择的值，以便在选择更改时可以访问它。但是考虑到我有很多组合框，这很容易出错，直到可以以不同的方式更新某些框。

提前感谢您的帮助

一个最小的工作示例：

import sys

from PyQt5.QtWidgets import (   QApplication, QWidget, QGridLayout, QComboBox,
                                QLabel)

class BaseWidget(QWidget):
    def __init__(self):
        super(BaseWidget, self).__init__()
        self.setGeometry(300, 300, 300, 200)

        # 2 Labels to display the new and the old item after selection
        self.LabelOldItem = QLabel(self)
        self.LabelNewItem = QLabel(self)

        self.MyCombobox = QComboBox(self)
        self.MyCombobox.addItems(['Item 1', 'Item 2', 'Item 3', 'Item 4'])
        self.MyCombobox.activated[str].connect(self.ComboChange)


        grid = QGridLayout()
        grid.addWidget(self.MyCombobox, 0, 0, 1, 1)
        grid.addWidget(self.LabelOldItem, 1, 0, 1, 1)
        grid.addWidget(self.LabelNewItem, 2, 0, 1, 1)

        self.setLayout(grid)

    def ComboChange(self, newitem):
        self.LabelOldItem.setText('Previous Selection: ') # <- crucial point
        # How can i transfer both, not only the new item but also the previous
        # item of the combobox when it gets activated?
        self.LabelNewItem.setText('New Selection: <b>' + newitem + '</b>')


if __name__ == '__main__':

    app = QApplication(sys.argv)

    pyqtComboExample = BaseWidget()
    pyqtComboExample.show()
    sys.exit(app.exec_())

Answer 1

一种可能的解决方案是创建一个自定义 QComboBox：

import sys
from PyQt5 import QtCore, QtWidgets


class ComboBox(QtWidgets.QComboBox):
    new_signal = QtCore.pyqtSignal(str, str)

    def __init__(self, parent=None):
        super(ComboBox, self).__init__(parent)
        self.lastSelected = ""
        self.activated[str].connect(self.onActivated)

    def onActivated(self, text):
        self.new_signal.emit(self.lastSelected, text)
        self.lastSelected = text


class BaseWidget(QtWidgets.QWidget):
    def __init__(self):
        super(BaseWidget, self).__init__()
        self.setGeometry(300, 300, 300, 200)

        # 2 Labels to display the new and the old item after selection
        self.LabelOldItem = QtWidgets.QLabel()
        self.LabelNewItem = QtWidgets.QLabel()

        self.MyCombobox = ComboBox()
        self.MyCombobox.addItems(['Item 1', 'Item 2', 'Item 3', 'Item 4'])
        self.MyCombobox.new_signal.connect(self.ComboChange)

        grid = QtWidgets.QGridLayout(self)
        grid.addWidget(self.MyCombobox, 0, 0, 1, 1)
        grid.addWidget(self.LabelOldItem, 1, 0, 1, 1)
        grid.addWidget(self.LabelNewItem, 2, 0, 1, 1)

    def ComboChange(self, lastitem, newitem):
        self.LabelOldItem.setText('Previous Selection: <b>{}</b>'.format(lastitem))
        self.LabelNewItem.setText('New Selection: <b>{}</b>'.format(newitem))


if __name__ == '__main__':

    app = QtWidgets.QApplication(sys.argv)
    pyqtComboExample = BaseWidget()
    pyqtComboExample.show()
    sys.exit(app.exec_())

另一种可能的解决方案是使用sender() 获取使用的QComboBox，并将旧项目保存在属性中：

import sys
from PyQt5 import QtCore, QtWidgets


class BaseWidget(QtWidgets.QWidget):
    def __init__(self):
        super(BaseWidget, self).__init__()
        self.setGeometry(300, 300, 300, 200)

        # 2 Labels to display the new and the old item after selection
        self.LabelOldItem = QtWidgets.QLabel()
        self.LabelNewItem = QtWidgets.QLabel()

        self.MyCombobox = QtWidgets.QComboBox()
        self.MyCombobox.addItems(['Item 1', 'Item 2', 'Item 3', 'Item 4'])
        self.MyCombobox.activated[str].connect(self.ComboChange)

        grid = QtWidgets.QGridLayout(self)
        grid.addWidget(self.MyCombobox, 0, 0, 1, 1)
        grid.addWidget(self.LabelOldItem, 1, 0, 1, 1)
        grid.addWidget(self.LabelNewItem, 2, 0, 1, 1)

    def ComboChange(self, newitem):
        combo = self.sender()
        lastitem = combo.property("lastitem")
        self.LabelOldItem.setText('Previous Selection: <b>{}</b>'.format(lastitem))
        self.LabelNewItem.setText('New Selection: <b>{}</b>'.format(newitem))
        combo.setProperty("lastitem", newitem)


if __name__ == '__main__':

    app = QtWidgets.QApplication(sys.argv)
    pyqtComboExample = BaseWidget()
    pyqtComboExample.show()
    sys.exit(app.exec_())