PySide QFtp下载0字节文件

Question

我正在使用PySide制作一个小型FTP客户端，我正试图在下载文件时获取进度条以进行更新。我告诉qftp对象监听dataTransferProgress信号，这样当进行一个方法时，会调用一个设置progressBar值的方法。但是，每次调用该方法时，实际存在的文件的最大值为-1。有什么我做错了吗？

来源：

import os
import platform
import sys
import threading
from ftplib import FTP

from PySide.QtCore import *
from PySide.QtGui import *
from PySide.QtNetwork import *
import ui_FTPWindow

class FtpWindow(QDialog, ui_FTPWindow.Ui_Dialog):
    def __init__(self, parent=None): 
        super(FtpWindow, self).__init__(parent)
        self.connected = False
        self.username = None
        #self.fileTree.itemActivated.connect(self.processItem)
        #self.fileTree.currentItemChanged.connect(self.enableDownloadButton)
        self.password = None    
        self.server = None
        self.port = None
        self.ftp = None
        self.qftp = QFtp(self)
        self.url = None
        self.folderIcon = None
        self.fileIcon = None
        self.currentDir = None
        self.count = 0

        #self.fileTree.setEnabled(False)
        self.setupUi(self)

        self.connectButton.clicked.connect(self.connectOrDisconnect)
        self.mkdirButton.clicked.connect(self.makedir)
        self.downloadButton.clicked.connect(self.download)

        self.updateUi()

    def updateUi(self):
        self.serverEdit.setText('ftpserverhere')
        self.progressBar.setValue(0);
        if self.serverEdit.text() is not None:
            self.connectButton.setEnabled(True)
        else:
            self.connectButton.setEnabled(False)

    def populateTree(self):
        self.fileTree.clear()
        self.consoleLabel.setText("Loading file tree..")
        root = QTreeWidgetItem(self.ftp.pwd())
        self.fileTree.addTopLevelItem(root)
        for item in self.ftp.nlst():
            child = QTreeWidgetItem()
            child.setText(0, item)
            root.addChild(child)
            root.setExpanded(True)
            if not "." in item:
                self.count = 1
                self.goDeeper(item, child)
            print item

    def connectOrDisconnect(self):
        self.url = QUrl(self.serverEdit.text());
        self.qftp = QFtp(self)
        self.qftp.commandFinished.connect(self.commandFinished)
        self.qftp.dataTransferProgress.connect(self.updateDataTransferProgress)
        print "ftp listeners set"
        if  "ftp" in self.url.scheme().lower():
            if self.url.userName():
                self.ftp = FTP(self.url.host(), self.url.userName(), self.url.password()) 
                self.currentDir = self.ftp.nlst()
                self.qftp.connectToHost(self.url.host())
                print self.qftp.currentCommand()

    def goDeeper(self, s, parent):
        for item in self.ftp.nlst(s):
            if item is None:
                return
            deeperChild = QTreeWidgetItem()
            deeperChild.setText(0, item)
            parent.addChild(deeperChild)
            if not "." in item:
                self.goDeeper(item, deeperChild)

    def download(self):
        fileName = self.fileTree.currentItem().text(0)

        if QFile.exists(fileName):
            QMessageBox.information(self, "FTP",
                    "There already exists a file called %s in the current "
                    "directory." % fileName)
            return

        self.outFile = QFile(fileName)
        if not self.outFile.open(QIODevice.WriteOnly):
            QMessageBox.information(self, "FTP",
                    "Unable to save the file %s: %s." % (fileName, self.outFile.errorString()))
            self.outFile = None
            return

        self.qftp.get(self.fileTree.currentItem().text(0), self.outFile)

        self.consoleLabel.setText("Downloading %s..." % fileName)
        self.downloadButton.setEnabled(False)

    def updateDataTransferProgress(self, readBytes, totalBytes):
        self.progressBar.setMaximum(totalBytes)
        self.progressBar.setValue(readBytes)
        print self.qftp.currentCommand()
        print totalBytes
        print readBytes

    def makedir(self):
        foldername = unicode(self.commandEdit.text())
        if self.commandEdit.text() != "":
            #self.qftp.rawCommand(unicode("mkdir " + foldername))

            self.qftp.mkdir(foldername )
            print self.qftp.currentCommand()
            self.consoleLabel.setText("Creating directory %s" % (foldername))

    def executeCommand(self):
        if self.commandEdit.text() == "":
            return
        else:
            command = self.commandEdit.text()
            self.qftp.rawCommand(command)

    def commandFinished(self, error):
        if str(self.qftp.currentCommand()) == 'PySide.QtNetwork.QFtp.Command.Mkdir':
            self.populateTree()
            self.consoleLabel.setText("Directory %s created" % self.commandEdit.text())
            self.commandEdit.setText("")

        if str(self.qftp.currentCommand()) == 'PySide.QtNetwork.QFtp.Command.ConnectToHost':
            self.qftp.login(unicode(self.url.userName), unicode(self.url.password))
            self.consoleLabel.setText("Connected to server: %s" % self.url.host())
            self.qftp.get('')
            print "Invisible file got"
            print "completed"

        if str(self.qftp.currentCommand()) == 'PySide.QtNetwork.QFtp.Command.Login':
            self.populateTree()
            self.consoleLabel.setText("Logged in as %s" % self.url.userName())


        if str(self.qftp.currentCommand()) == 'Pyside.QtNetwork.QFtp.Get':
            if error:
                self.consoleLabel.setText("Canceled download of %s." % self.outFile.fileName())
                self.outFile.close()
                self.outFile.remove()
            else:
                self.consoleLabel.setText("Downloaded %s to current directory." % self.outFile.fileName())
                self.outFile.close()

def main():
    app = QApplication(sys.argv)
    app.setOrganizationName("Qtrac Ltd.")
    app.setOrganizationDomain("qtrac.eu")
    app.setApplicationName("Image Changer")
    form = FtpWindow()
    form.show()
    app.exec_()

main()

非常感谢！