在Qt与Http通信的时候,会根据不同的情况使用同步或者异步的方式进行数据请求。
同步,即发送Http请求之后,会一直等待服务器返回的数据,接收到数据之前,程序一直阻塞。
异步,即发送Http请求之后,程序可以继续往下执行,接收到服务器返回的数据时自动调用其对应的槽函数处理数据。
同步需要在发送请求之后,放置一个QEnentLoop,而异步只需要绑定对应的槽函数即可。
同步Demo:
QUrl url(myurl);
QNetworkReply *reply = quitmanager->get(QNetworkRequest(QUrl(url)));
QEventLoop eventLoop;
connect(quitmanager, SIGNAL(finished(QNetworkReply*)), &eventLoop, SLOT(quit()));
eventLoop.exec(); //block until finish
//reply->readall()
reply->deleteLater();
reply = nullptr;
return true;
异步Demo:
QNetworkAccessManager *manager = new QNetworkAccessManager;
QNetworkRequest *request = new QNetworkRequest;
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(finishedSlot(QNetworkReply*)));//绑定槽函数
//get post请求二选一
QUrl url(urlHead+"exam_start/"+studentId);
request->setUrl(url);
manager->get(*request);//发送get请求
QByteArray postData = document.toJson(QJsonDocument::Compact);
request->setUrl(url);
request->setHeader(QNetworkRequest::ContentTypeHeader,QVariant("application/json"));
manager->post(*request, postData);//发送post请求
槽函数
void MainWindow::finishedSlot(QNetworkReply *reply)
{
qDebug() << "进入函数: " << __FUNCTION__;
QString json = reply->readAll();//这个返回的JSON包所携带的所有信息
QJsonParseError jsonerror;
QJsonDocument doc = QJsonDocument::fromJson(json.toUtf8(), &jsonerror);
if (!doc.isNull() && jsonerror.error == QJsonParseError::NoError)
{
QJsonObject object = doc.object();
if(object.contains("type"))
{
switch (object.value("type").toInt())
{
case 1:parseLogJason(object);break;
case 2:parseParameterJason(object);break;
case 3:parseExamStartJason(object);break;
case 4:parseExamEndJason(object);break;
default:return;
}
}
}
}
异步也可以将槽函数写在函数内 依然是异步
QNetworkAccessManager* manager6 = new QNetworkAccessManager(this);
// 准备工作 - 初始化一个QNetworkRequest
QNetworkRequest res6;
//设置头 - 浏览器
res6.setHeader(QNetworkRequest::UserAgentHeader,
"Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/59.0.3071.115 Safari/537.36");
res6.setUrl(QUrl("http://" + IP + "/version"));
QNetworkReply* reply6 = manager6->get(res6);
reply6->attribute(QNetworkRequest::HttpStatusCodeAttribute);
reply6->attribute(QNetworkRequest::RedirectionTargetAttribute);
// 读服务器回写的数据
connect(reply6, &QNetworkReply::readyRead, this, [=]()
{
//QVariant str = reply6->header(QNetworkRequest::LocationHeader);
QByteArray data = reply6->readAll();
//qDebug() << "version "<< data ;
QString str = QString(data);
int pos = str.indexOf('-');
version[node_id] = str.mid(pos + 3, 2) + "."+ str.mid(0, pos ) ;
reply6->abort();
reply6->close();
reply6->deleteLater();
manager6->deleteLater();
});