QT：用QWebSocket實現webchannel，實現C++與HTML通訊

CGWLMXUP發表於2019-02-18
QTWebC++HTML

基本原理是通過channel將C++物件暴露給HTML，在HTML中呼叫qwebchannel.js。前提是建立transport，QT只提供了一個抽象基類QWebChannelAbstractTransport，需要自己進行實現，官方建議用QWebSocket實現，並給出了例項。

1、實現Transport類，內建一個WebSocket套接字；

2、實現新的channel類，內建一個WebSocketServer;

3、利用新的channel註冊C++物件，從而HTML可以使用該物件；

4、通過以下三種方式進行C++與HTML的互動：

4.1 在HTML中l連線C++ signal與js函式的

object.signal.connect(function(){});

4.2 在HTML中呼叫C++ public slots函式；

4.3 在HTML中呼叫C++ Q_INVOKABLE修飾的函式；

 

下面給出例項程式碼

 

5.1 WebSocketTransport類

websockettransport.h

 1 #ifndef WEBSOCKETTRANSPORT_H
 2 #define WEBSOCKETTRANSPORT_H
 3 
 4 #include <QWebChannelAbstractTransport>
 5 
 6 QT_BEGIN_NAMESPACE
 7 class QWebSocket;
 8 QT_END_NAMESPACE
 9 
10 class WebSocketTransport : public QWebChannelAbstractTransport
11 {
12     Q_OBJECT
13 public:
14     explicit WebSocketTransport(QWebSocket *socket);
15     virtual ~WebSocketTransport();
16 
17     void sendMessage(const QJsonObject &message) override;
18 
19 private slots:
20     void textMessageReceived(const QString &message);
21 
22 private:
23     QWebSocket *m_socket;
24 };
25 
26 #endif // WEBSOCKETTRANSPORT_H

websockettransport.cpp

 1 #include "websockettransport.h"
 2 
 3 #include <QDebug>
 4 #include <QJsonDocument>
 5 #include <QJsonObject>
 6 #include <QWebSocket>
 7 
 8 
 9 /*!
10     Construct the transport object and wrap the given socket.
11 
12     The socket is also set as the parent of the transport object.
13 */
14 WebSocketTransport::WebSocketTransport(QWebSocket *socket)
15 : QWebChannelAbstractTransport(socket)
16 , m_socket(socket)
17 {
18     connect(socket, &QWebSocket::textMessageReceived,
19             this, &WebSocketTransport::textMessageReceived);
20     connect(socket, &QWebSocket::disconnected,
21             this, &WebSocketTransport::deleteLater);
22 }
23 
24 /*!
25     Destroys the WebSocketTransport.
26 */
27 WebSocketTransport::~WebSocketTransport()
28 {
29     m_socket->deleteLater();
30 }
31 
32 /*!
33     Serialize the JSON message and send it as a text message via the WebSocket to the client.
34 */
35 void WebSocketTransport::sendMessage(const QJsonObject &message)
36 {
37     QJsonDocument doc(message);
38     m_socket->sendTextMessage(QString::fromUtf8(doc.toJson(QJsonDocument::Compact)));
39 }
40 
41 /*!
42     Deserialize the stringified JSON messageData and emit messageReceived.
43 */
44 void WebSocketTransport::textMessageReceived(const QString &messageData)
45 {
46     QJsonParseError error;
47     QJsonDocument message = QJsonDocument::fromJson(messageData.toUtf8(), &error);
48     if (error.error) {
49         qWarning() << "Failed to parse text message as JSON object:" << messageData
50                    << "Error is:" << error.errorString();
51         return;
52     } else if (!message.isObject()) {
53         qWarning() << "Received JSON message that is not an object: " << messageData;
54         return;
55     }
56     emit messageReceived(message.object(), this);
57 }

5.2 WebSocketChannel類

websocketchannel.h

#ifndef WEBSOCKETCHANNEL_H
#define WEBSOCKETCHANNEL_H

#include <QWebChannel>

class QWebSocketServer;
class WebSocketTransport;

//繼承QWebchannel類，在內部建立socket server與transport中socket的連線

class WebSocketChannel : public QWebChannel
{
    Q_OBJECT
public:
    WebSocketChannel(QWebSocketServer *server);

signals:
    void clientConnected(WebSocketTransport *client);

private slots:
    void handleNewConnection();

private:
    QWebSocketServer *_server;
};

#endif // WEBSOCKETCHANNEL_H

 

websocketchannel.cpp

#include "websocketchannel.h"
#include <QWebSocketServer>
#include "websockettransport.h"

WebSocketChannel::WebSocketChannel(QWebSocketServer *server)
    :_server(server)
{
    connect(server, &QWebSocketServer::newConnection,
            this, &WebSocketChannel::handleNewConnection);

    connect(this, &WebSocketChannel::clientConnected,
            this, &WebSocketChannel::connectTo);//connectTo槽繼承自QWebchannel
}

void WebSocketChannel::handleNewConnection()
{
    emit clientConnected(new WebSocketTransport(_server->nextPendingConnection()));
}

 

main.cpp

#include <QApplication>
#include <QDesktopServices>
#include <QDialog>
#include <QDir>
#include <QFileInfo>
#include <QUrl>
#include <QWebChannel>
#include <QWebSocketServer>


int main(int argc, char** argv)
{
    QApplication app(argc, argv);
    
    //建立QWebSocketServer，url是ws://localhost:12345

    QWebSocketServer server(QStringLiteral("QWebChannel Standalone Example Server"), QWebSocketServer::NonSecureMode);
    if (!server.listen(QHostAddress::LocalHost, 12345)) {
        qFatal("Failed to open web socket server.");
        return 1;
    }
    
    //建立websocketchannl,該channel就可以用來通訊了
    WebSocketChannel channel(&server);

    // setup the UI
    Dialog dialog;

    // setup the core and publish it to the QWebChannel
    Core core(&dialog);
    
    //註冊C++物件，該類要繼承自QObject
    channel.registerObject(QStringLiteral("core"), &core);

    // open a browser window with the client HTML page
    QUrl url = QUrl::fromLocalFile(BUILD_DIR "/index.html");
    QDesktopServices::openUrl(url);

    dialog.displayMessage(Dialog::tr("Initialization complete, opening browser at %1.").arg(url.toDisplayString()));
    dialog.show();

    return app.exec();
}

index.html

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
         //使用qwebchannel.js
        <script type="text/javascript" src="./qwebchannel.js"></script>
        <script type="text/javascript">
            //BEGIN SETUP
            function output(message) {
                var output = document.getElementById("output");
                output.innerHTML = output.innerHTML + message + "\n";
            }
            window.onload = function() {
                var baseUrl = "ws://localhost:12345";

                output("Connecting to WebSocket server at " + baseUrl + ".");
                var socket = new WebSocket(baseUrl);

                socket.onclose = function() {
                    console.error("web channel closed");
                };
                socket.onerror = function(error) {
                    console.error("web channel error: " + error);
                };
                socket.onopen = function() {
                    output("WebSocket connected, setting up QWebChannel.");
                    new QWebChannel(socket, function(channel) {
                        // make core object accessible globally
                        window.core = channel.objects.core;


                        document.getElementById("send").onclick = function() {
                            var input = document.getElementById("input");
                            var text = input.value;
                            if (!text) {
                                return;
                            }

                            output("Sent message: " + text);
                            input.value = "";
                            
                            //呼叫C++公有槽函式
                            core.receiveText(text);
                            core.hello(text);
                        }
                        
                        //連線C++訊號與javascript函式
                        core.sendText.connect(function(message) {
                            output("Received message: " + message);
                        });

                        core.receiveText("Client connected, ready to send/receive messages!");
                        output("Connected to WebChannel, ready to send/receive messages!");
                    });
                }
            }
            //END SETUP
        </script>
        <style type="text/css">
            html {
                height: 100%;
                width: 100%;
            }
            #input {
                width: 400px;
                margin: 0 10px 0 0;
            }
            #send {
                width: 90px;
                margin: 0;
            }
            #output {
                width: 500px;
                height: 300px;
            }
        </style>
    </head>
    <body>
        <textarea id="output"></textarea><br />
        <input id="input" /><input type="submit" id="send" value="Send" onclick="javascript:click();" />
    </body>
</html>

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