QT下用QTcpSocket传输文件， 调用了QTcpSocket:write()但是如何没有bytesWritten信号上来

QT下用QTcpSocket传输文件， 调用了QTcpSocket::write()但是怎么没有bytesWritten信号上来
最近看Qt 的网络编程关于Tcp传输文件的问题， （按照这个文章实现的[url]http://www.yafeilinux.com/?p=806[/url]), 
但是我很郁闷的是为什么我的tcpSender中的bytesWritten(quint64)信号没有上来， 刚开始的连接都是正常的。 望高手指点。
  
tcpsender.cpp 

#include <qfiledialog.h> 
#include "tcpsender.h"

tcpSender::tcpSender(QWidget *parent, Qt::WFlags flags)
 : QMainWindow(parent, flags)
{
 loadSize = 4 * 1024;
 totalBytes = 0;
 bytesWrittenAA = 0;
 bytesToWrite = 0;
 tcpClient = new QTcpSocket(this);
 connect(tcpClient, SIGNAL(connected()), this, SLOT(startTransfer()));
 connect(tcpClient, SIGNAL(bytesWritten(quint64)), this, SLOT(updateClientProgress(qint64)));
 connect(tcpClient, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(displayError(QAbstractSocket::SocketError)));
 
 ui.setupUi(this);
 ui.sendButton->setEnabled(false); 
 
}
tcpSender::~tcpSender()
{
}

void tcpSender::OpenFile()
{
 fileName = QFileDialog::getOpenFileName(this);
 if (!fileName.isEmpty())
 {
  ui.sendButton->setEnabled(true);
  ui.clientStatusLabel->setText(tr("打开文件 %1成功!").arg(fileName));
 }
}
void tcpSender::send()
{
 ui.sendButton->setEnabled(false);
 bytesWrittenAA = 0;
 ui.clientStatusLabel->setText(tr("连接中..."));
 tcpClient->connectToHost(ui.hostLineEdit->text(), ui.portLineEdit->text().toInt());
}
void tcpSender::startTransfer()
{
 localFile = new QFile(fileName);
 if (!localFile->open(QFile::ReadOnly))
 {
  qDebug() << "open file error!";
  return;
 }
 totalBytes = localFile->size();
 QDataStream sendOut(&outBlock, QIODevice::WriteOnly);
 sendOut.setVersion(QDataStream::Qt_4_6);
 QString currentFileName = fileName.right(fileName.size() - fileName.lastIndexOf("/") - 1);
 sendOut << qint64(0) << qint64(0) << currentFileName;
 totalBytes += outBlock.size();
 sendOut.device()->seek(0);
 sendOut << totalBytes << qint64((outBlock.size() - sizeof(qint64) * 2));
 bytesToWrite = totalBytes - tcpClient->write(outBlock);
 ui.clientStatusLabel->setText(tr("已连接"));
 outBlock.resize(0); 
}

void tcpSender::updateClientProgress(qint64 numBytes)
{
 bytesWrittenAA += numBytes;
 if (bytesWrittenAA > 0)
 {
  outBlock = localFile->read(qMin(bytesToWrite, loadSize));
  bytesToWrite -= (int)tcpClient->write(outBlock);
  outBlock.resize(0);
 }
 else
 {
  localFile->close();
 }
 ui.clientProgressBar->setMaximum(totalBytes);
 ui.clientProgressBar->setValue(bytesWrittenAA);
 if (bytesWrittenAA == totalBytes)
 {
  ui.clientStatusLabel->setText(tr("传输文件 %1成功").arg(fileName));
  localFile->close();
  tcpClient->close();
 }
}

void tcpSender::displayError(QAbstractSocket::SocketError)
{
 qDebug() << tcpClient->errorString();
 tcpClient->close();
 ui.clientProgressBar->reset();
 ui.clientStatusLabel->setText(tr("客户端就绪"));
 ui.sendButton->setEnabled(true);
}

void tcpSender::on_openButton_clicked() 
{
 OpenFile();
}
void tcpSender::on_sendButton_clicked()
{
 send(); 
}
 

//tcpreceiver.cpp
#include "tcpreceiver.h"