python - QListWidget 处理来自点击和 itemSelectionChanged 的​​多个信号

Question

我有两个列表小部件，它们本质上是项目选择器。当我在任一列表中选择一个项目时，我需要它来触发一个方法。这里只有一个程序有问题。我需要在选择更改或单击某个项目时发生该过程，但我不希望这种情况发生两次，这是我遇到的问题

它有点难以描述，但请看下面的代码。

场景一:两个列表都只连接“itemSelectionChanged” 点击“奶酪” 点击“否” 两者现在都已选中，当您交替单击它们时，没有任何反应，因为没有选择发生变化，但是当我从不同的列表中选择一个项目时，我需要调用 something_happened 方法。

场景 2:两个列表都只连接“已点击” 单击时会发生一些事情，但是当我单击并拖动以更改选择时，不会触发任何事件，因为“单击”没有发生并且 itemSelectionChanged 未连接到任何东西。 I need the something_happened method to be called when the selection changes in this manner also.

场景 3:两个列表都连接“itemSelectionChanged”和“clicked” 单击并拖动以更改选择会发生某些事情(好)，但是当我在新项目上单击“单击”时，会发送两个信号，并且我想要发生的事件会发生两次(坏)。

鉴于上述情况，我想同时实现以下所有目标:

• 当我点击一个新项目时处理只有一个事件(同时发出 itemSelectionChanged 和 itemClicked 导致两个事件)
• 在我点击一个已选择的项目(它发出 itemClicked 信号)时处理一个事件
• 在我通过单击和拖动更改选择时处理一个事件(这会发出 itemSelectionChagned 信号)

示例代码如下:

from PyQt4 import QtGui
QtWidgets = QtGui
# from PyQt5 import QtWidgets
import sys
import time


def something_happened():
    print(time.time())

app = QtWidgets.QApplication(sys.argv)

widget = QtWidgets.QWidget(None)
vlay = QtWidgets.QVBoxLayout(widget)

list_widget1 = QtWidgets.QListWidget(None)
list_widget1.setSelectionMode(QtWidgets.QAbstractItemView.ExtendedSelection)
list_widget1.addItems(("Cheese", "Whiz", "tastes", "great"))
list_widget1.itemSelectionChanged.connect(something_happened)
list_widget1.clicked.connect(something_happened)

list_widget2 = QtWidgets.QListWidget(None)
list_widget2.setSelectionMode(QtWidgets.QAbstractItemView.ExtendedSelection)
list_widget2.addItems(("No", "it", "tastes", "bad"))
list_widget2.itemSelectionChanged.connect(something_happened)
# list_widget2.clicked.connect(something_happened)

vlay.addWidget(list_widget1)
vlay.addWidget(list_widget2)

widget.show()

app.exec_()

Answer 1

在这个例子中，我继承了 QListWidget。这不是必需的，但我认为如果将选择更改的决定封装在小部件本身中，它会使代码更清晰。我制作了两种类型的小部件，每种小部件在决定选择是否更改方面都有自己的行为。您可以尝试使用 mousePress/mouseRelease/selectionChanged 组合，希望这段代码能为您提供所需的工具。 运行该程序，并注意两个小部件之间的差异。

class SomeFrame(object):
    """A container to place all the widgets, and control
       present the output from the selections.
    """
    def __init__(self):
        self.frame = QtWidgets.QFrame()

        # Creating content
        list_widget1 = MyQListWidgetA()
        list_widget1.setSelectionMode(QtWidgets.QAbstractItemView.ExtendedSelection)
        list_widget1.addItems(("Cheese", "Whiz", "tastes", "great"))

        list_widget2 = MyQListWidgetB()
        list_widget2.setSelectionMode(QtWidgets.QAbstractItemView.ExtendedSelection)
        list_widget2.addItems(("No", "it", "tastes", "bad"))

        # Creating Layout
        layout = QtWidgets.QHBoxLayout()
        layout.addWidget(list_widget1)
        layout.addWidget(list_widget2)

        self.frame.setLayout(layout)

        # Connections
        from functools import partial
        list_widget1.selection_changed.connect(partial(self.selectionChangedCB, 'list_1'))
        list_widget2.selection_changed.connect(partial(self.selectionChangedCB, 'list_2'))

        self.frame.show()

    def selectionChangedCB(self, list_name, selected_items):
        print(list_name + ' changed: ' + str(selected_items))


from PyQt5 import QtWidgets, QtCore
class MyQListWidgetA(QtWidgets.QListWidget):
    """This widget emits selection_changed whenever its
       itemSelectionChanged signal is emitted, AND there
       was an actual change in the selected items.
    """
    selection_changed = QtCore.pyqtSignal(object)

    def __init__(self):
        QtWidgets.QListWidget.__init__(self)

        self.selected_items = set()

        self.itemSelectionChanged.connect(self.something_happened)

    def something_happened(self):
        # Create a set of the newly selected items, so we can compare
        # to the old selected items set
        newly_selected_items = set([item.text() for item in self.selectedItems()])
        if newly_selected_items != self.selected_items:
            # Only emit selection_changed signal if a change was detected.
            self.selected_items = newly_selected_items
            self.selection_changed.emit(self.selected_items)


class MyQListWidgetB(QtWidgets.QListWidget):
    """This widget emits selection_changed whenever it is pressed
       (mimic "clicked" signal) and again when the user is done
       selecting the items (mouse release) IFF the selection
       has changed.
    """
    selection_changed = QtCore.pyqtSignal(object)

    def __init__(self):
        QtWidgets.QListWidget.__init__(self)

        self.selected_items = set()

    def something_happened(self, initial_click=False):
        # Create a set of the newly selected items, so we can
        # compare to the old selected items set
        newly_selected_items = set([item.text() for item in self.selectedItems()])
        if newly_selected_items != self.selected_items:
            # Only emit selection_changed signal if a change was detected
            self.selected_items = newly_selected_items
            self.selection_changed.emit(self.selected_items)

    def mousePressEvent(self, event):
        QtWidgets.QListWidget.mousePressEvent(self, event)
        self.something_happened()

    def mouseReleaseEvent(self, event):
        QtWidgets.QListWidget.mouseReleaseEvent(self, event)
        self.something_happened()


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)         
    theFrame = SomeFrame()
    sys.exit(app.exec_())

编辑:我意识到我从来没有考虑过“当我点击一个已经选择的项目(它发出 itemClicked 信号)时处理一个事件”。 我把它看作是同一个单项点击，但它也可以解决同一个多项目点击(使用 mouseReleaseEvent，并比较旧列表和新列表)。 只需添加 MyQListWidgetC，并将其连接到它的两个信号。 B 和 C 之间的主要区别在于，在 mousePressEvent 中，我们检查是否按下了单个项目，以及它是否是同一项目。

class MyQListWidgetC(QtWidgets.QListWidget):
    """This widget emits selection_changed whenever it is pressed
       (mimic "clicked" signal) and again when the user is done
       selecting the items (mouse release) IFF the selection
       has changed. If a single item was clicked, AND it is the
       same item, the widget will emit same_item_clicked, which
       the owner can listen to and decide what to do.
    """
    selection_changed = QtCore.pyqtSignal(object)
    same_item_clicked = QtCore.pyqtSignal(object)

    def __init__(self):
        QtWidgets.QListWidget.__init__(self)

        self.selected_items = set()

    def something_happened(self, initial_click=False):
        # Create a set of the newly selected items, so we can
        # compare to the old selected items set
        newly_selected_items = set([item.text() for item in self.selectedItems()])
        if newly_selected_items != self.selected_items:
            # Only emit selection_changed signal if a change was detected
            self.selected_items = newly_selected_items
            self.selection_changed.emit(self.selected_items)

    def mousePressEvent(self, event):
        QtWidgets.QListWidget.mousePressEvent(self, event)
        newly_selected_items = set([item.text() for item in self.selectedItems()])
        if len(newly_selected_items) == 1 and newly_selected_items == self.selected_items:
            self.same_item_clicked.emit(self.selected_items)
        else:
            self.something_happened()

    def mouseReleaseEvent(self, event):
        QtWidgets.QListWidget.mouseReleaseEvent(self, event)
        self.something_happened()