在QHeaderView和QListWidget之间拖放列

Question

我在使用QHeaderView拖放功能时遇到了麻烦。当我子类一个QHeaderView时，我能够接受没有问题的下降。但是，当我单击QHeaderView并尝试从其中一个列中拖动时，似乎不会发生任何事情。

下面，我重新实现了几个拖动事件，以便在调用它们时简单地打印出来。然而，只有dragEnterEvent是成功的。从来没有调用过像startDrag这样的其他事件。我的最终目标是拥有一个QTableView，在这里我可以将列拖到QListWidget (实质上隐藏了该列)，然后如果用户希望该列及其数据再次可见，则可以将QListWidget项拖回QTableView。但是，除非我能够理解为什么QHeaderView不允许我拖动，否则我就无法继续前进。任何帮助都将不胜感激。

class MyHeader(QHeaderView):
    def __init__(self, parent=None):
        super().__init__(Qt.Horizontal, parent)
        self.setDragEnabled(True)
        self.setAcceptDrops(True)

    def startDrag(self, *args, **kwargs):
        print('start drag success')

    def dragEnterEvent(self, event):
        print('drag enter success')

    def dragLeaveEvent(self, event):
        print('drag leave success')

    def dragMoveEvent(self, event):
        print('drag move success')

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

        listWidget = QListWidget()
        listWidget.setDragEnabled(True)
        listWidget.setAcceptDrops(True)
        listWidget.addItem('item #1')
        listWidget.addItem('item #2')

        tableWidget = QTableWidget()
        header = MyHeader()
        tableWidget.setHorizontalHeader(header)
        tableWidget.setRowCount(5)
        tableWidget.setColumnCount(2)
        tableWidget.setHorizontalHeaderLabels(["Column 1", "Column 2"])

        splitter = QSplitter(Qt.Horizontal)
        splitter.addWidget(listWidget)
        splitter.addWidget(tableWidget)
        layout = QHBoxLayout()
        layout.addWidget(splitter)
        self.setLayout(layout)

if __name__=='__main__':
    import sys
    app = QApplication(sys.argv)
    form= Form()
    form.show()
    sys.exit(app.exec_())

Answer 1

QHeaderView类不使用从QAbstractItemView继承的拖放方法，因为它从不需要启动拖动操作。拖放只用于重新排列列，并且没有必要为此使用QDrag机制。

有鉴于此，必须实现自定义拖放处理(使用mousePressEvent、mouseMoveEvent和dropEvent)，并提供编码和解码Qt用于在视图之间传递项的mime数据格式的功能。表小部件需要一个事件筛选器，以便在隐藏所有列时仍然可以删除；对于列表小部件，也需要停止将项复制到自身。

下面的演示脚本实现了所有这些。也许还需要更多的改进，但这应该足以让您开始：

import sys
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *

class MyHeader(QHeaderView):
    MimeType = 'application/x-qabstractitemmodeldatalist'
    columnsChanged = pyqtSignal(int)

    def __init__(self, parent=None):
        super().__init__(Qt.Horizontal, parent)
        self.setDragEnabled(True)
        self.setAcceptDrops(True)
        self._dragstartpos = None

    def encodeMimeData(self, items):
        data = QByteArray()
        stream = QDataStream(data, QIODevice.WriteOnly)
        for column, label in items:
            stream.writeInt32(0)
            stream.writeInt32(column)
            stream.writeInt32(2)
            stream.writeInt32(int(Qt.DisplayRole))
            stream.writeQVariant(label)
            stream.writeInt32(int(Qt.UserRole))
            stream.writeQVariant(column)
        mimedata = QMimeData()
        mimedata.setData(MyHeader.MimeType, data)
        return mimedata

    def decodeMimeData(self, mimedata):
        data = []
        stream = QDataStream(mimedata.data(MyHeader.MimeType))
        while not stream.atEnd():
            row = stream.readInt32()
            column = stream.readInt32()
            item = {}
            for count in range(stream.readInt32()):
                key = stream.readInt32()
                item[key] = stream.readQVariant()
            data.append([item[Qt.UserRole], item[Qt.DisplayRole]])
        return data

    def mousePressEvent(self, event):
        if event.button() == Qt.LeftButton:
            self._dragstartpos = event.pos()
        super().mousePressEvent(event)

    def mouseMoveEvent(self, event):
        if (event.buttons() & Qt.LeftButton and
            self._dragstartpos is not None and
            (event.pos() - self._dragstartpos).manhattanLength() >=
            QApplication.startDragDistance()):
            column = self.logicalIndexAt(self._dragstartpos)
            data = [column, self.model().headerData(column, Qt.Horizontal)]
            self._dragstartpos = None
            drag = QDrag(self)
            drag.setMimeData(self.encodeMimeData([data]))
            action = drag.exec(Qt.MoveAction)
            if action != Qt.IgnoreAction:
                self.setColumnHidden(column, True)

    def dropEvent(self, event):
        mimedata = event.mimeData()
        if mimedata.hasFormat(MyHeader.MimeType):
            if event.source() is not self:
                for column, label in self.decodeMimeData(mimedata):
                    self.setColumnHidden(column, False)
                event.setDropAction(Qt.MoveAction)
                event.accept()
            else:
                event.ignore()
        else:
            super().dropEvent(event)

    def setColumnHidden(self, column, hide=True):
        count = self.count()
        if 0 <= column < count and hide != self.isSectionHidden(column):
            if hide:
                self.hideSection(column)
            else:
                self.showSection(column)
            self.columnsChanged.emit(count - self.hiddenSectionCount())

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

        self.listWidget = QListWidget()
        self.listWidget.setAcceptDrops(True)
        self.listWidget.setDragEnabled(True)
        self.listWidget.viewport().installEventFilter(self)

        self.tableWidget = QTableWidget()
        header = MyHeader(self)
        self.tableWidget.setHorizontalHeader(header)
        self.tableWidget.setRowCount(5)
        self.tableWidget.setColumnCount(4)

        labels = ["Column 1", "Column 2", "Column 3", "Column 4"]
        self.tableWidget.setHorizontalHeaderLabels(labels)
        for column, label in enumerate(labels):
            if column > 1:
                item = QListWidgetItem(label)
                item.setData(Qt.UserRole, column)
                self.listWidget.addItem(item)
                header.hideSection(column)

        header.columnsChanged.connect(
            lambda count: self.tableWidget.setAcceptDrops(not count))
        self.tableWidget.viewport().installEventFilter(self)

        splitter = QSplitter(Qt.Horizontal)
        splitter.addWidget(self.listWidget)
        splitter.addWidget(self.tableWidget)
        layout = QHBoxLayout()
        layout.addWidget(splitter)
        self.setLayout(layout)

    def eventFilter(self, source, event):
        if event.type() == QEvent.Drop:
            if source is self.tableWidget.viewport():
                self.tableWidget.horizontalHeader().dropEvent(event)
                return True
            else:
                event.setDropAction(Qt.MoveAction)
        return super().eventFilter(source, event)

if __name__=='__main__':

    app = QApplication(sys.argv)
    form = Form()
    form.setGeometry(600, 50, 600, 200)
    form.show()
    sys.exit(app.exec_())