1、简介

此示例演示一个简单的HTTP客户端如何从远程主机获取文件。

2、使用类

QUrl：url抽象类
QUrl::fromUserInput：从QString转换成QUrl
QNetworkAccessManager：网络访问API围绕一个QNetworkAccessManager对象构造，该对象保存其发送的请求的通用配置和设置。创建QNetworkAccessManager对象后，应用程序可以使用它通过网络发送请求。提供了一组标准函数，这些函数接受一个请求和可选数据，并且每个函数都返回一个QNetworkReply对象。返回的对象用于获取响应于相应请求而返回的任何数据。
QNetworkRequest：发送的请求
QNetworkReply：收到的回应

QNetworkAccessManager、QNetworkRequest、QNetworkReply一组简单的用法如下：

QNetworkRequest request;
request.setUrl(QUrl("http://qt-project.org"));
request.setRawHeader("User-Agent", "MyOwnBrowser 1.0");

QNetworkReply *reply = manager->get(request);
connect(reply, &QIODevice::readyRead, this, &MyClass::slotReadyRead);
connect(reply, &QNetworkReply::errorOccurred,
        this, &MyClass::slotError);
connect(reply, &QNetworkReply::sslErrors,
        this, &MyClass::slotSslErrors);

本例中主要用法如下，重点关注QNetworkReply的各种信号的使用，
如：QNetworkReply::finished、QIODevice::readyRead、QNetworkReply::downloadProgress、QNetworkReply::finished

	// QNetworkAccessManager qnam；
    QNetworkReply *reply = qnam.get(QNetworkRequest(url));
    connect(reply, &QNetworkReply::finished, this, &HttpWindow::httpFinished);
    connect(reply, &QIODevice::readyRead, this, &HttpWindow::httpReadyRead);

    ProgressDialog *progressDialog = new ProgressDialog(url, this);
    connect(reply, &QNetworkReply::downloadProgress, progressDialog, &ProgressDialog::networkReplyProgress);
    connect(reply, &QNetworkReply::finished, progressDialog, &ProgressDialog::hide);
    progressDialog->show();