From Gossip@caterpillar

Qt4 Gossip: QTcpServer

QTcpSocket 用來與遠端伺服器連線，如果您要接受客戶端連線，則使用QTcpServer，QTcpServer使用listen()方法開始傾開所指定的連接埠，您 可以使用isListening()方法測試是否正在傾聽連線，當連線發生時，QTcpServer會發出newConnection()的 Signal，您可以使用QTcpServer的nextPendingConnection()取得代表客戶端連線的QTcpSocket物件，接下來 就可以使用它來與客戶端進行資料傳輸。

配合 QTcpSocket 中的範例，以下製作一個ServerDialog來接受客戶端的檔案傳送，首先是ServerDialog的定義：
  • ServerDialog.h
#ifndef SERVERDIALOG_H
#define SERVERDIALOG_H

#include <QDialog>
#include <QTcpServer>

class QLabel;
class QFile;
class QTcpSocket;

class ServerDialog : public QDialog {
   Q_OBJECT
   
public:
    ServerDialog(QWidget *parent = 0);
    void setReceivedFileName(QString fileName);
    void listen(quint16 port);
    
public slots:
    void acceptConnection();
    void updateProgress();
    void displayError(QAbstractSocket::SocketError socketError);

private:
    QLabel *label;
    QTcpServer server;
    QTcpSocket *clientConnection;
    int bytesReceived;
    QFile *file;
};

#endif

當連線發生時，QTcpServer會發出newConnection()的 Signal，程式中將之連接至acceptConnection()，而每當有資料可以準備讀取時，代表客戶端連線的QTcpSocket會發出 readyRead()信號，這將之連接至updateProgress()，當中將進行檔案儲存與目前接受容量顯示，以下為實作內容：
  • ServerDialog.cpp
#include <QApplication>
#include <QProgressBar>
#include <QVBoxLayout>
#include <QHostAddress>
#include <QLabel>
#include <QAbstractSocket>
#include <QTcpSocket>
#include <QMessageBox>
#include <QFile>

#include <iostream>
using namespace std;

#include "ServerDialog.h"

ServerDialog::ServerDialog(QWidget *parent) : QDialog(parent) {
    label = new QLabel("Received:");
    QVBoxLayout *layout = new QVBoxLayout;
    layout->addWidget(label);
    this->setLayout(layout);
    
    connect(&server, SIGNAL(newConnection()), 
            this, SLOT(acceptConnection()));
}

void ServerDialog::setReceivedFileName(QString fileName) {
    file = new QFile(fileName);
}

void ServerDialog::listen(quint16 port) {
    server.listen(QHostAddress::Any, port);
}

void ServerDialog::acceptConnection() {
    if (!file->open(QIODevice::WriteOnly)) {
        cerr << "Unable to write the file" << endl;
        delete file;
        file = 0;
        return;
    }    
    
    clientConnection = server.nextPendingConnection();
    
    connect(clientConnection, SIGNAL(readyRead()), 
            this, SLOT(updateProgress()));
    connect(clientConnection, SIGNAL(error(QAbstractSocket::SocketError)),
            this, SLOT(displayError(QAbstractSocket::SocketError)));
    
    server.close();
    
    QApplication::setOverrideCursor(Qt::WaitCursor);
}

void ServerDialog::updateProgress() {
    bytesReceived += (int) clientConnection->bytesAvailable();
    file->write(clientConnection->readAll());
    
    QString txt = "Received %1MB";
    
    label->setText(txt.arg(bytesReceived / (1024 * 1024)));
}

void ServerDialog::displayError(QAbstractSocket::SocketError socketError) {
    file->close();
    
    if (socketError == QTcpSocket::RemoteHostClosedError) {
        QMessageBox::information(this, 
               "OK!", "Save file as " + file->fileName());
    }
    else {
        QMessageBox::information(this, "Network error",
           "The following error occurred: " + clientConnection->errorString());
    }
    
    delete file;
    file = 0;
    
    QApplication::restoreOverrideCursor();
}

您可以用以下方式來使用ServerDialog：
ServerDialog *server = new ServerDialog;
server->setReceivedFileName("f://received.dat");
server->listen(9393);
server->setWindowTitle("QTcpServer");
server->resize(200, 10);
server->show();

下圖為執行時的參考畫面：