PyQt：如何在dropEvent中获取QListWidget的listItem.data()

Question

这里有两个 QListWidget（列表控件）。每个列表项都通过 setData(QtCore.Qt.UserRole, myClassInstA) 这个方法，给它分配了一个 MyClass() 的实例。

当你点击下方的 QListWidget 中的某个列表项时，可以通过以下方式打印出被点击项的数据：

.data(QtCore.Qt.UserRole).toPyObject()

但是，如果你把上方 QListWidget 中的某个项拖到下方的 QListWidget 上，那个项的数据就会显示为 None（没有数据）。有趣的是，点击同一个项时却能打印出数据。我在想，是否可以在 droppedOnB() 这个函数中获取到存储在列表项中的数据（这样 droppedOnB() 就能打印出这个项中的数据）。

---

from PyQt4 import QtGui, QtCore
import sys, os

class MyClass(object):
        def __init__(self):
            super(MyClass, self).__init__()               

class ThumbListWidget(QtGui.QListWidget):
    _drag_info = []
    def __init__(self, type, name, parent=None):
        super(ThumbListWidget, self).__init__(parent)
        self.setObjectName(name)
        self.setIconSize(QtCore.QSize(124, 124))
        self.setDragDropMode(QtGui.QAbstractItemView.DragDrop)
        self.setSelectionMode(QtGui.QAbstractItemView.ExtendedSelection)
        self.setAcceptDrops(True)
        self._dropping = False

    def startDrag(self, actions):
        self._drag_info[:] = [str(self.objectName())]
        for item in self.selectedItems():
            self._drag_info.append(self.row(item))
        super(ThumbListWidget, self).startDrag(actions)

    def dragEnterEvent(self, event):
        if event.mimeData().hasUrls():
            event.accept()
        else:
            super(ThumbListWidget, self).dragEnterEvent(event)

    def dragMoveEvent(self, event):
        if event.mimeData().hasUrls():
            event.setDropAction(QtCore.Qt.CopyAction)
            event.accept()
        else:
            super(ThumbListWidget, self).dragMoveEvent(event)

    def dropEvent(self, event):
        if event.mimeData().hasUrls():
            event.setDropAction(QtCore.Qt.CopyAction)
            event.accept()
            links = []
            for url in event.mimeData().urls():
                links.append(str(url.toLocalFile()))
            self.emit(QtCore.SIGNAL("dropped"), links)
        else:
            # event.setDropAction(QtCore.Qt.MoveAction)
            self._dropping = True
            super(ThumbListWidget, self).dropEvent(event)
            self._dropping = False

    def rowsInserted(self, parent, start, end):
        if self._dropping:
            self._drag_info.append((start, end))
            self.emit(QtCore.SIGNAL("dropped"), self._drag_info)
        super(ThumbListWidget, self).rowsInserted(parent, start, end)


class Dialog_01(QtGui.QMainWindow):
    def __init__(self):
        super(QtGui.QMainWindow,self).__init__()
        self.listItems={}

        myQWidget = QtGui.QWidget()
        myBoxLayout = QtGui.QVBoxLayout()
        myQWidget.setLayout(myBoxLayout)
        self.setCentralWidget(myQWidget)

        self.listWidgetA = ThumbListWidget(self, 'MainTree')
        self.listWidgetB = ThumbListWidget(self, 'SecondaryTree')
        self.listWidgetB.setDragDropMode(QtGui.QAbstractItemView.DropOnly)

        for i in range(7):
            listItemA=QtGui.QListWidgetItem()
            listItemA.setText('A'+'%04d'%i)
            self.listWidgetA.addItem(listItemA)

            myClassInstA=MyClass()
            listItemA.setData(QtCore.Qt.UserRole, myClassInstA)

            listItemB=QtGui.QListWidgetItem()
            listItemB.setText('B'+'%04d'%i)
            self.listWidgetB.addItem(listItemB)

            myClassInstB=MyClass()
            listItemB.setData(QtCore.Qt.UserRole, myClassInstB)

        myBoxLayout.addWidget(self.listWidgetA)      

        myBoxLayout.addWidget(self.listWidgetB)   
        self.connect(self.listWidgetB, QtCore.SIGNAL("dropped"), self.droppedOnB)
        self.listWidgetB.clicked.connect(self.itemClicked)


    def droppedOnB(self, dropped_list):
        print '\n\t droppedOnB()', dropped_list, dropped_list[-1]

        destIndexes=dropped_list[-1]
        for index in range(destIndexes[0],destIndexes[-1]+1):
            dropedItem=self.listWidgetB.item(index)
            modelIndex=self.listWidgetB.indexFromItem(dropedItem)
            dataObject = modelIndex.data(QtCore.Qt.UserRole).toPyObject()
            print '\n\t\t droppedOnB()', type(modelIndex), type(dataObject)

    def itemClicked(self, modelIndex):      
        dataObject = modelIndex.data(QtCore.Qt.UserRole).toPyObject()
        print 'itemClicked(): ' ,type(modelIndex), type(dataObject)


if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    dialog_1 = Dialog_01()
    dialog_1.show()
    dialog_1.resize(720,480)
    sys.exit(app.exec_())

Answer 1

最终的目标是把MyClassA的实例data对象（和itemA关联）替换成MyClassB，这个替换发生在itemA被拖放到listWidgetB之后。

当itemA被放到目标listWidgetB时，它的data是空的。如果你试图用itemA.data(QtCore.Qt.UserRole).toPyObject()来获取它，会返回None（这个操作是在droppedOnB()方法中进行的，这个方法是拖放事件触发后第一个被调用的）。

尝试给刚刚放下的列表项赋值或重新赋值，甚至删除它，都会导致后面出现各种意想不到的问题。我使用了.setHidden(True)来隐藏它。

以下是步骤：

1. 获取源列表项及其数据。
2. 获取目标（被放下的）项并将其隐藏。
3. 声明一个MyClassB()的实例。
4. 创建一个新的列表项。使用.setData(QtCore.Qt.UserRole, myClassInstB)将上一步创建的MyClassB()实例对象分配给这个列表项。
5. 将新的列表项添加到ListWidget中。

下面是一个可运行的代码。再次强调，itemA在创建时被分配了ClassA的一个实例。
当itemA被放到listWidgetB上后，放下的项会被隐藏，并用另一个项替代，这个替代项分配了classB的实例。

from PyQt4 import QtGui, QtCore
import sys, os, copy

class MyClassA(object):
        def __init__(self):
            super(MyClassA, self).__init__()               

class MyClassB(object):
        def __init__(self):
            super(MyClassB, self).__init__()
            self.DataObjectCopy=None  

class ThumbListWidget(QtGui.QListWidget):
    _drag_info = []
    def __init__(self, type, name, parent=None):
        super(ThumbListWidget, self).__init__(parent)
        self.setObjectName(name)
        self.setIconSize(QtCore.QSize(124, 124))
        self.setDragDropMode(QtGui.QAbstractItemView.DragDrop)
        self.setSelectionMode(QtGui.QAbstractItemView.ExtendedSelection)
        self.setAcceptDrops(True)
        self._dropping = False

    def startDrag(self, actions):
        self._drag_info[:] = [str(self.objectName())]
        for item in self.selectedItems():
            self._drag_info.append(self.row(item))
        super(ThumbListWidget, self).startDrag(actions)

    def dragEnterEvent(self, event):
        if event.mimeData().hasUrls():
            event.accept()
        else:
            super(ThumbListWidget, self).dragEnterEvent(event)

    def dragMoveEvent(self, event):
        if event.mimeData().hasUrls():
            event.setDropAction(QtCore.Qt.CopyAction)
            event.accept()
        else:
            super(ThumbListWidget, self).dragMoveEvent(event)

    def dropEvent(self, event):
        if event.mimeData().hasUrls():
            event.setDropAction(QtCore.Qt.CopyAction)
            event.accept()
            links = []
            for url in event.mimeData().urls():
                links.append(str(url.toLocalFile()))
            self.emit(QtCore.SIGNAL("dropped"), links)
        else:
            # event.setDropAction(QtCore.Qt.MoveAction)
            self._dropping = True
            super(ThumbListWidget, self).dropEvent(event)
            self._dropping = False

    def rowsInserted(self, parent, start, end):
        if self._dropping:
            self._drag_info.append((start, end))
            self.emit(QtCore.SIGNAL("dropped"), self._drag_info)
        super(ThumbListWidget, self).rowsInserted(parent, start, end)


class Dialog_01(QtGui.QMainWindow):
    def __init__(self):
        super(QtGui.QMainWindow,self).__init__()
        self.listItems={}

        myQWidget = QtGui.QWidget()
        myBoxLayout = QtGui.QVBoxLayout()
        myQWidget.setLayout(myBoxLayout)
        self.setCentralWidget(myQWidget)

        self.listWidgetA = ThumbListWidget(self, 'MainTree')
        self.listWidgetB = ThumbListWidget(self, 'SecondaryTree')
        self.listWidgetB.setDragDropMode(QtGui.QAbstractItemView.DropOnly)

        for i in range(3):
            listItemA=QtGui.QListWidgetItem()
            listItemA.setText('A'+'%04d'%i)
            self.listWidgetA.addItem(listItemA)

            myClassInstA=MyClassA()
            listItemA.setData(QtCore.Qt.UserRole, myClassInstA)

            listItemB=QtGui.QListWidgetItem()
            listItemB.setText('B'+'%04d'%i)
            self.listWidgetB.addItem(listItemB)

            myClassInstB=MyClassB()
            listItemB.setData(QtCore.Qt.UserRole, myClassInstB)

        myBoxLayout.addWidget(self.listWidgetA)      

        myBoxLayout.addWidget(self.listWidgetB)   
        self.connect(self.listWidgetB, QtCore.SIGNAL("dropped"), self.droppedOnB)
        self.listWidgetB.clicked.connect(self.itemClicked)


    def droppedOnB(self, dropped_list):
        if not dropped_list or len(dropped_list)<3: return       

        srcIndexes=dropped_list[1:-1]
        destIndexes=dropped_list[-1]

        # build a list of corresponding src-to-dest indexes sets
        itemsIndxes=[]
        i=0
        for num in range(destIndexes[0], destIndexes[-1]+1):
            itemsIndxes.append((srcIndexes[i], num))
            i+=1 

        print '\n\t droppedOnB(): dropped_list =',dropped_list,'; srcIndexes =',srcIndexes,'; destIndexes =',destIndexes, '; itemsIndxes =',itemsIndxes

        for indexSet in itemsIndxes:
            srcNum = indexSet[0]
            destIndxNum = indexSet[-1]

            # Get source listItem's data object
            srcItem=self.listWidgetA.item(srcNum)
            if not srcItem: continue
            srcItemData = srcItem.data(QtCore.Qt.UserRole)
            if not srcItemData: continue
            srcItemDataObject=srcItemData.toPyObject()
            if not srcItemDataObject: continue
            # make a deepcopy of src data object
            itemDataObject_copy=copy.deepcopy(srcItemDataObject)

            # get dropped item
            droppedItem=self.listWidgetB.item(destIndxNum)
            # hide dropped item since removing it results to mess
            droppedItem.setHidden(True)
            # declare new ClassB instance
            myClassInstB=MyClassB()
            myClassInstB.DataObjectCopy=itemDataObject_copy

            # create a new listItem
            newListItem=QtGui.QListWidgetItem()
            newListItem.setData(QtCore.Qt.UserRole, myClassInstB)
            newListItem.setText(srcItem.text())
            self.listWidgetB.blockSignals(True)
            self.listWidgetB.addItem(newListItem)
            self.listWidgetB.blockSignals(False)


    def itemClicked(self, modelIndex):      
        dataObject = modelIndex.data(QtCore.Qt.UserRole).toPyObject()
        print 'itemClicked(): instance type:', type(dataObject)


if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    dialog_1 = Dialog_01()
    dialog_1.show()
    dialog_1.resize(720,480)
    sys.exit(app.exec_())