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，转移新选择非常简单：

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

但是，当索引更改时，我如何设法不仅将新选择的项目而且将上一个项目传递给函数？

我的折衷解决方案是为每个存储最后选择的值的组合框手动设置一个变量，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，直到某些框可以以不同的方式更新。

在此先感谢您的帮助

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

一个可能的解决方案是创建自定义 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:

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_())

在 QComboBox 激活时获取上一个和新选择的项目

Get previous and newly selected item on activation in QComboBox

python

pyqt

qcombobox

pyqt5