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

Question

There are two QListWidgets. Every list item was assigned MyClass()'s instance using setData(QtCore.Qt.UserRole, myClassInstA) .

Clicking a lower QListWidget's listItem prints out a clicked listItem's data retrieved using:

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

Any itemA dragged and dropped from top QListWidget onto a lower shows None for data. Interesting that clicking the same item prints there is a data. I wonder if it is possible to retrieve a data stored in listItem within droppedOnB() function (so droppedOnB() is able to print out the data stored in a item).

---

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

The ultimate goal was to replace MyClassA 's instance data -object (attached to itemA) with MyClassB after itemA is dropped onto listWidgetB.

When itemA is dropped onto the destination listWidgetB the itemA arrives with no data stored. It returns None if you try to retrieve it with itemA.data(QtCore.Qt.UserRole).toPyObject() (if done inside of droppedOnB() - a method triggered first onDrop event).

Trying to assign, reassign a data to just dropped listItem... or even removing it causes all kind of surprises later. I am using .setHidden(True).

Those are the steps:

1. Get source listItem and its data.
2. Get destination (dropped) item and hide it.
3. Declare MyClassB() instance
4. Create new list item. Assign created in previous step MyClassB() instance object to listItem using .setData(QtCore.Qt.UserRole, myClassInstB)
5. Add new listItem to ListWidget.

Here is a functional code. Once again, itemA is assign an instance of ClassA on creation. After itemA is dropped onto listWidgetB a dropped item is hidden and 'substituted' with another item to which classB instance is assigned.

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_())