官方解析

Fortune Client Example
以使用QTcpSocket为例子，服务端可以配合Fortune Server或Threaded Fortune Server。
本例把QDataStream作为传输协议，从服务端获取字符串。
从下面对QTcpSocket的介绍，官方给出了2种比较好的调用方法：
一种使用信号与槽达到异步的效果（个人是非常推荐这个的）；
一种是使用多线程，在非GUI线程进行阻塞（估计是留给老一辈程序员，个人觉得这个程序结构性会更为通用些）。

  class Client : public QDialog{Q_OBJECTpublic:explicit Client(QWidget *parent = Q_NULLPTR);private slots:void requestNewFortune();void readFortune();void displayError(QAbstractSocket::SocketError socketError);void enableGetFortuneButton();void sessionOpened();private:QComboBox *hostCombo;QLineEdit *portLineEdit;QLabel *statusLabel;QPushButton *getFortuneButton;QTcpSocket *tcpSocket;QDataStream in;QString currentFortune;QNetworkSession *networkSession;};

这里的QDataStream对象是给QTcpSocket这个指针使用的。

下面new了一个QTcpSocket，并且设置了parent，这样就不用程序员自己释放了。

  Client::Client(QWidget *parent): QDialog(parent), hostCombo(new QComboBox), portLineEdit(new QLineEdit), getFortuneButton(new QPushButton(tr("Get Fortune"))), tcpSocket(new QTcpSocket(this)), networkSession(Q_NULLPTR){setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);...in.setDevice(tcpSocket);in.setVersion(QDataStream::Qt_4_0);

这里是基于QDataStream，这个文档里面说，要把客户端和服务器都设置为同一个版本的流协议（这里目前先这个记着，个人觉得应该是网络传输序列
化的问题，后期将会给出QDataStream的详细讲解）

当接收到数据时候会触发QTcpSocket::readyRead()信号，当有错误的的时候，会触发QTcpSocket::error()信号。

...connect(tcpSocket, &QIODevice::readyRead, this, &Client::readFortune);connect(tcpSocket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error),...}

按下Get Fortune按钮后会进入requestNewFortune这个槽函数：

  void Client::requestNewFortune(){getFortuneButton->setEnabled(false);tcpSocket->abort();tcpSocket->connectToHost(hostCombo->currentText(),portLineEdit->text().toInt());}

使用abort()函数，终止以前的连接，使用connectToHost()来创建一个新连接。

下面来看下错误提示的函数：

  void Client::displayError(QAbstractSocket::SocketError socketError){switch (socketError) {case QAbstractSocket::RemoteHostClosedError:break;case QAbstractSocket::HostNotFoundError:QMessageBox::information(this, tr("Fortune Client"),tr("The host was not found. Please check the ""host name and port settings."));break;case QAbstractSocket::ConnectionRefusedError:QMessageBox::information(this, tr("Fortune Client"),tr("The connection was refused by the peer. ""Make sure the fortune server is running, ""and check that the host name and port ""settings are correct."));break;default:QMessageBox::information(this, tr("Fortune Client"),tr("The following error occurred: %1.").arg(tcpSocket->errorString()));}getFortuneButton->setEnabled(true);}

下面是readyRead()函数：

  void Client::readFortune(){in.startTransaction();QString nextFortune;in >> nextFortune;if (!in.commitTransaction())return;if (nextFortune == currentFortune) {QTimer::singleShot(0, this, &Client::requestNewFortune);return;}currentFortune = nextFortune;statusLabel->setText(currentFortune);getFortuneButton->setEnabled(true);}

上这个代码是重点中的重点，各种tcp面试和项目中都会用到的思路。不能想当然的认为可以一次性接收到数据包，然后展示，在网络传输中，可能被
路由器或其他设备分成小包，特别是网络比较慢的时候，可能是几个碎片接收。但在Qt中当readyRead()信号被触发时候，所有的碎片都被整合了，我
们直接用就可以了，但我个人觉得，至少得搞清楚Qt为开发者做了什么。至于他是怎么做到的，以后有机会再去研究吧。

QString nextFortune;
in >> nextFortune;if (!in.commitTransaction())return;

这个代码，就是在读取没有完整的时候进行回滚，如果读取完整，就不回滚了。

实例代码

这里我把官方代码上的版权去掉了，方面看，在此说明下

client.h

#ifndef CLIENT_H
#define CLIENT_H#include <QDialog>
#include <QTcpSocket>
#include <QDataStream>QT_BEGIN_NAMESPACE
class QComboBox;
class QLabel;
class QLineEdit;
class QPushButton;
class QTcpSocket;
class QNetworkSession;
QT_END_NAMESPACE//! [0]
class Client : public QDialog
{Q_OBJECTpublic:explicit Client(QWidget *parent = Q_NULLPTR);private slots:void requestNewFortune();void readFortune();void displayError(QAbstractSocket::SocketError socketError);void enableGetFortuneButton();void sessionOpened();private:QComboBox *hostCombo;QLineEdit *portLineEdit;QLabel *statusLabel;QPushButton *getFortuneButton;QTcpSocket *tcpSocket;QDataStream in;QString currentFortune;QNetworkSession *networkSession;
};
//! [0]#endif

client.cpp

#include <QtWidgets>
#include <QtNetwork>#include "client.h"//! [0]
Client::Client(QWidget *parent): QDialog(parent), hostCombo(new QComboBox), portLineEdit(new QLineEdit), getFortuneButton(new QPushButton(tr("Get Fortune"))), tcpSocket(new QTcpSocket(this)), networkSession(Q_NULLPTR)
{setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
//! [0]hostCombo->setEditable(true);// find out name of this machineQString name = QHostInfo::localHostName();if (!name.isEmpty()) {hostCombo->addItem(name);QString domain = QHostInfo::localDomainName();if (!domain.isEmpty())hostCombo->addItem(name + QChar('.') + domain);}if (name != QLatin1String("localhost"))hostCombo->addItem(QString("localhost"));// find out IP addresses of this machineQList<QHostAddress> ipAddressesList = QNetworkInterface::allAddresses();// add non-localhost addressesfor (int i = 0; i < ipAddressesList.size(); ++i) {if (!ipAddressesList.at(i).isLoopback())hostCombo->addItem(ipAddressesList.at(i).toString());}// add localhost addressesfor (int i = 0; i < ipAddressesList.size(); ++i) {if (ipAddressesList.at(i).isLoopback())hostCombo->addItem(ipAddressesList.at(i).toString());}portLineEdit->setValidator(new QIntValidator(1, 65535, this));QLabel *hostLabel = new QLabel(tr("&Server name:"));hostLabel->setBuddy(hostCombo);QLabel *portLabel = new QLabel(tr("S&erver port:"));portLabel->setBuddy(portLineEdit);statusLabel = new QLabel(tr("This examples requires that you run the ""Fortune Server example as well."));getFortuneButton->setDefault(true);getFortuneButton->setEnabled(false);QPushButton *quitButton = new QPushButton(tr("Quit"));QDialogButtonBox *buttonBox = new QDialogButtonBox;buttonBox->addButton(getFortuneButton, QDialogButtonBox::ActionRole);buttonBox->addButton(quitButton, QDialogButtonBox::RejectRole);//! [1]in.setDevice(tcpSocket);in.setVersion(QDataStream::Qt_4_0);
//! [1]connect(hostCombo, &QComboBox::editTextChanged,this, &Client::enableGetFortuneButton);connect(portLineEdit, &QLineEdit::textChanged,this, &Client::enableGetFortuneButton);connect(getFortuneButton, &QAbstractButton::clicked,this, &Client::requestNewFortune);connect(quitButton, &QAbstractButton::clicked, this, &QWidget::close);
//! [2] //! [3]connect(tcpSocket, &QIODevice::readyRead, this, &Client::readFortune);
//! [2] //! [4]connect(tcpSocket, QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error),
//! [3]this, &Client::displayError);
//! [4]QGridLayout *mainLayout = Q_NULLPTR;if (QGuiApplication::styleHints()->showIsFullScreen() || QGuiApplication::styleHints()->showIsMaximized()) {QVBoxLayout *outerVerticalLayout = new QVBoxLayout(this);outerVerticalLayout->addItem(new QSpacerItem(0, 0, QSizePolicy::Ignored, QSizePolicy::MinimumExpanding));QHBoxLayout *outerHorizontalLayout = new QHBoxLayout;outerHorizontalLayout->addItem(new QSpacerItem(0, 0, QSizePolicy::MinimumExpanding, QSizePolicy::Ignored));QGroupBox *groupBox = new QGroupBox(QGuiApplication::applicationDisplayName());mainLayout = new QGridLayout(groupBox);outerHorizontalLayout->addWidget(groupBox);outerHorizontalLayout->addItem(new QSpacerItem(0, 0, QSizePolicy::MinimumExpanding, QSizePolicy::Ignored));outerVerticalLayout->addLayout(outerHorizontalLayout);outerVerticalLayout->addItem(new QSpacerItem(0, 0, QSizePolicy::Ignored, QSizePolicy::MinimumExpanding));} else {mainLayout = new QGridLayout(this);}mainLayout->addWidget(hostLabel, 0, 0);mainLayout->addWidget(hostCombo, 0, 1);mainLayout->addWidget(portLabel, 1, 0);mainLayout->addWidget(portLineEdit, 1, 1);mainLayout->addWidget(statusLabel, 2, 0, 1, 2);mainLayout->addWidget(buttonBox, 3, 0, 1, 2);setWindowTitle(QGuiApplication::applicationDisplayName());portLineEdit->setFocus();QNetworkConfigurationManager manager;if (manager.capabilities() & QNetworkConfigurationManager::NetworkSessionRequired) {// Get saved network configurationQSettings settings(QSettings::UserScope, QLatin1String("QtProject"));settings.beginGroup(QLatin1String("QtNetwork"));const QString id = settings.value(QLatin1String("DefaultNetworkConfiguration")).toString();settings.endGroup();// If the saved network configuration is not currently discovered use the system defaultQNetworkConfiguration config = manager.configurationFromIdentifier(id);if ((config.state() & QNetworkConfiguration::Discovered) !=QNetworkConfiguration::Discovered) {config = manager.defaultConfiguration();}networkSession = new QNetworkSession(config, this);connect(networkSession, &QNetworkSession::opened, this, &Client::sessionOpened);getFortuneButton->setEnabled(false);statusLabel->setText(tr("Opening network session."));networkSession->open();}
//! [5]
}
//! [5]//! [6]
void Client::requestNewFortune()
{getFortuneButton->setEnabled(false);tcpSocket->abort();
//! [7]tcpSocket->connectToHost(hostCombo->currentText(),portLineEdit->text().toInt());
//! [7]
}
//! [6]//! [8]
void Client::readFortune()
{in.startTransaction();QString nextFortune;in >> nextFortune;if (!in.commitTransaction())return;if (nextFortune == currentFortune) {QTimer::singleShot(0, this, &Client::requestNewFortune);return;}currentFortune = nextFortune;statusLabel->setText(currentFortune);getFortuneButton->setEnabled(true);
}
//! [8]//! [13]
void Client::displayError(QAbstractSocket::SocketError socketError)
{switch (socketError) {case QAbstractSocket::RemoteHostClosedError:break;case QAbstractSocket::HostNotFoundError:QMessageBox::information(this, tr("Fortune Client"),tr("The host was not found. Please check the ""host name and port settings."));break;case QAbstractSocket::ConnectionRefusedError:QMessageBox::information(this, tr("Fortune Client"),tr("The connection was refused by the peer. ""Make sure the fortune server is running, ""and check that the host name and port ""settings are correct."));break;default:QMessageBox::information(this, tr("Fortune Client"),tr("The following error occurred: %1.").arg(tcpSocket->errorString()));}getFortuneButton->setEnabled(true);
}
//! [13]void Client::enableGetFortuneButton()
{getFortuneButton->setEnabled((!networkSession || networkSession->isOpen()) &&!hostCombo->currentText().isEmpty() &&!portLineEdit->text().isEmpty());}void Client::sessionOpened()
{// Save the used configurationQNetworkConfiguration config = networkSession->configuration();QString id;if (config.type() == QNetworkConfiguration::UserChoice)id = networkSession->sessionProperty(QLatin1String("UserChoiceConfiguration")).toString();elseid = config.identifier();QSettings settings(QSettings::UserScope, QLatin1String("QtProject"));settings.beginGroup(QLatin1String("QtNetwork"));settings.setValue(QLatin1String("DefaultNetworkConfiguration"), id);settings.endGroup();statusLabel->setText(tr("This examples requires that you run the ""Fortune Server example as well."));enableGetFortuneButton();
}

main.cpp

#include <QApplication>
#include "client.h"int main(int argc, char *argv[])
{QApplication app(argc, argv);QGuiApplication::setApplicationDisplayName(Client::tr("Fortune Client"));Client client;client.show();return app.exec();
}

博主增加解析

本实例中还有QNetworkConfigurationManager、QNetworkConfiguration、QNetworkSession目前暂时这么理解，对网络进行某种配置，这里要当把服务器看完之后，将会给出这些管理的详细介绍。

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Qt文档阅读笔记-Fortune Client Example实例解析

官方解析

实例代码

博主增加解析

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