pyQT QNetworkManager和ProgressBars

我试图编写一些代码,从Web服务器下载一个文件并保存它,在QProgressBar中显示下载进度。 现在,有很多方法可以在常规Python中实现这一点,而且很简单。问题是它会锁定progressBar的刷新。解决方案是使用PyQT的QNetworkManager类。我可以很好地下载东西,只是无法在进度栏上显示进度。举个例子:

class Form(QDialog):

    def __init__(self,parent=None):
        super(Form,self).__init__(parent)
        self.progressBar = QProgressBar()
        self.reply = None
        layout = QHBoxLayout()
        layout.addWidget(self.progressBar)
        self.setLayout(layout)
        self.manager = QNetworkAccessManager(self)
        self.connect(self.manager,SIGNAL("finished(QNetworkReply*)"),self.replyFinished)
        self.Down()

    def Down(self):

        address = QUrl("http://stackoverflow.com") #URL from the remote file.
        self.manager.get(QNetworkRequest(address))
    def replyFinished(self, reply):
        self.connect(reply,SIGNAL("downloadProgress(int,int)"),self.progressBar, SLOT("setValue(int)"))
        self.reply = reply
        self.progressBar.setMaximum(reply.size())
        alltext = self.reply.readAll()
        #print alltext
        #print alltext
    def updateBar(self, read,total):
        print "read", read
        print "total",total
        #self.progressBar.setMinimum(0)
        #self.progressBar.setMask(total)
        #self.progressBar.setValue(read)

在这种情况下,我的方法“updateBar”永远不会被调用。。。有什么想法吗?