关于QFtp下载的有关问题

#include "widget.h"#include "ui_widget.h"Widget::Widget(QWidget *parent) :    QWidget(parent),    ui(new Ui::Widget){    ui->setupUi(this);    ftp = new QFtp(this);    ftp->connectToHost("ftp.qt.nokia.com"); //连接到服务器    ftp->login();   //登录    ftp->cd("qt");   //跳转到“qt”目录下    QFile *file = new QFile("INSTALL");    if (!file->open(QIODevice::WriteOnly))    {        delete file;        return;    }    ftp->get("INSTALL", file);    connect(ftp,SIGNAL(commandStarted(int)),this,SLOT(ftpCommandStarted(int)));    connect(ftp,SIGNAL(commandFinished(int,bool)),this,SLOT(ftpCommandFinished(int,bool)));    ftp->close();   //关闭连接}Widget::~Widget(){    delete ui;}void Widget::changeEvent(QEvent *e){    QWidget::changeEvent(e);    switch (e->type()) {    case QEvent::LanguageChange:        ui->retranslateUi(this);        break;    default:        break;    }}void Widget::ftpCommandStarted(int){    if(ftp->currentCommand() == QFtp::ConnectToHost)    {        ui->label->setText(tr("正在连接到服务器..."));    }    if(ftp->currentCommand() == QFtp::Login)    {        ui->label->setText(tr("正在登录..."));    }    if(ftp->currentCommand() == QFtp::Get)    {        ui->label->setText(tr("正在下载..."));    }    else if(ftp->currentCommand() == QFtp::Close)    {        ui->label->setText(tr("正在关闭连接..."));    }}void Widget::ftpCommandFinished(int,bool error){    if(ftp->currentCommand() == QFtp::ConnectToHost)    {        if(error)            ui->label->setText(tr("连接服务器出现错误：%1").arg(ftp->errorString()));        else            ui->label->setText(tr("连接到服务器成功"));        return;    }    if(ftp->currentCommand() == QFtp::Login)    {        if(error)            ui->label->setText(tr("登录出现错误：%1").arg(ftp->errorString()));        else        {            ui->label->setText(tr("登录成功"));        }    }    if(ftp->currentCommand() == QFtp::Get)    {        if(error)            ui->label->setText(tr("下载出现错误：%1").arg(ftp->errorString()));        else        {            ui->label->setText(tr("已经完成下载"));            ui->textBrowser->setText(ftp->readAll());        }    }    else if (ftp->currentCommand() == QFtp::Close)    {        ui->label->setText(tr("已经关闭连接"));    }}