The function CheckSite() is called with an url like http://example.com, it initializes a QNetworkAccessManager object and connect() slots and signals.
The manger->get() call seems work (it generates http traffic) but does not call the slot replyFinished() at the request end.
What's wrong with this code?
#include <QtCore>
#include <QtNetwork>
class ClientHandler : public QObject
{
Q_OBJECT
QNetworkAccessManager *manager;
private slots:
void replyFinished(QNetworkReply *);
public:
void CheckSite(QString url);
};
void ClientHandler::replyFinished(QNetworkReply *reply) { qDebug() << "DONE"; }
void ClientHandler::CheckSite(QString url) {
QUrl qrl(url);
manager = new QNetworkAccessManager(this);
connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
manager->get(QNetworkRequest(qrl));
}
Nothing. I wrapped it so it was fully functional and it works fine:
// placed in client.cpp
#include <QtDebug>
#include <QCoreApplication>
/* YOUR CODE */
int main(int argc, char *argv[])
{
QCoreApplication app(argc, argv);
ClientHandler handler;
handler.CheckSite("www.google.com");
return app.exec();
}
#include "client.moc"
It output "DONE" as expected. Maybe the site you're checking really isn't returning? Maybe it needs authentication or is producing ssl errors?
What code do you have around that? Do you spin an event loop somewhere? e.g. qapp.exec() ?
Related
I am trying to connect a QThread::finished on another thread with an event loop in order to request a quit()
Consider this code :
#include <QApplication>
#include <QDebug>
#include <QThread>
class DummyThread : public QThread
{
public:
DummyThread::DummyThread(QObject *parent = nullptr) : QThread(parent){}
protected:
virtual void run() override{
QThread::sleep(1);
qDebug()<<"Work done!";
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QThread masterThread;
DummyThread childThread;
// This connection is Queued but doesn't work, you can force direct connection but this is not what I want...
QObject::connect(&childThread, &QThread::finished, &masterThread, &QThread::quit /*, Qt::ConnectionType::DirectConnection*/);
childThread.start();
masterThread.start(); //do a exec()
masterThread.wait();
return 0; //No need for an event loop here
}
This is a dummy exemple just to understand the problem here, the connection should be queued and the quit() executed in the masterThread event loop.
But nothing happens here :-(
What am I doing wrong here ?
I've wrote this code looking at examples online of how I'm supposed to run a console program that doesn't just run and quit and one that does. Based on a Qt console application. This one here, I wanted it to quit. I've understood pretty much everthing excepth the QTimer::singleShot line. If the line is commented out, the application will run but will not quit. If it is left, the application will run and quit as expected. Can anyone explain to me why?
dostuff.h
#ifndef DOSTUFF_H
#define DOSTUFF_H
#include <QObject>
#include <iostream>
class DoStuff: public QObject
{
Q_OBJECT
public :
DoStuff(QObject *parent = 0);
public slots:
void run();
signals:
void finished();
};
#endif // DOSTUFF_H
And the implementation dostuff.cpp
#include "dostuff.h"
DoStuff::DoStuff(QObject *parent):QObject(parent)
{
}
void DoStuff::run(){
for (int i = 0; i < 10000; i++){
std::cout << "Processing " << i << std::endl;
}
emit(finished());
}
My main.cpp
#include <QCoreApplication>
#include <QTimer>
#include "dostuff.h"
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
DoStuff *dostuff = new DoStuff(&a);
QObject::connect(dostuff,SIGNAL(finished()),&a,SLOT(quit()));
dostuff->run();
// WHY THIS??
QTimer::singleShot(10,dostuff,SLOT(run()));
return a.exec();
}
QTimer is not required to exit properly; You just need to provide a way to get your application to break the event loop at some point. In GUI application, Qt does that automatically when the last window is closed.
In Console applications, you can:
Either run your application without an event loop (if you have a straight-forward simple control flow in your application).
Or (if you require an event loop to handle some events or cross thread signal/slots) you need to have some event that makes your application break the event loop and quit. This event should only be triggered when the application has finished its job.
The code sample you have in your question is really simple, and does not require an event loop to run properly. The only effect the QTimer has in your code is that it delays execution for 10 ms. Here is the same code sample without running an event loop:
#include <QtCore>
class DoStuff: public QObject
{
Q_OBJECT
public :
DoStuff(QObject *parent = 0) : QObject(parent) {}
public slots:
void run() {
for (int i = 0; i < 10000; i++){
qInfo() << "Processing " << i;
}
emit finished();
}
signals:
void finished();
};
int main(int argc, char *argv[]) {
QCoreApplication a(argc, argv);
DoStuff dostuff;
QObject::connect(&dostuff, &DoStuff::finished,
&a, &QCoreApplication::quit);
dostuff.run();
return 0; //no event loop required
}
#include "main.moc"
If you start an event loop, you may notice that the quit slot does not work when not using QTimer::singleShot. The reason for this is that quit is called before the event loop is even started (and the call has no effect at all). That's why according to the docs, it is recommended to connect to quit using a queued connection:
It's good practice to always connect signals to this slot using a QueuedConnection. If a signal connected (non-queued) to this slot is emitted before control enters the main event loop (such as before "int main" calls exec()), the slot has no effect and the application never exits. Using a queued connection ensures that the slot will not be invoked until after control enters the main event loop.
So, if you want to have an event loop in your code above, you just need to connect using a Qt::QueuedConnection:
#include <QtCore>
class DoStuff: public QObject
{
Q_OBJECT
public :
DoStuff(QObject *parent = 0) : QObject(parent) {}
public slots:
void run() {
for (int i = 0; i < 10000; i++){
qInfo() << "Processing " << i;
}
emit finished();
}
signals:
void finished();
};
int main(int argc, char *argv[]) {
QCoreApplication a(argc, argv);
DoStuff dostuff;
QObject::connect(&dostuff, &DoStuff::finished,
&a, &QCoreApplication::quit,
Qt::QueuedConnection);
// ^^^^^^^^^^^^^^^^
// use a queued connection
dostuff.run();
return a.exec(); //start an event loop
}
#include "main.moc"
Timer is needed to postpone execution. Since you want to have a running event loop, a.exec() has to be called, then the timer executes your code. When your code finishes running, it triggers finished signal, that is tied to QCoreApplication::quit - that's the needed exit for event loop running inside a.exec().
Btw, you have to remove: dostuff->run(); from your code.
I'm trying to do a simple GET request (with modified User-Agent), return response to QML and do a JSON parsing.
Actually it only returns page content when loading is complete but it doesn't return it to QML.
Sorry for the noob question. I'm new to this language and I'm trying to learn it :)
Here's my code:
Home.qml
function getRequest() {
[...]
console.log('Request...')
var jsonResult = JSON.parse(connectNet.connectUrl("http://myURL.com/index.php").toString())
lbOutput.text = jsonResult.predictions[0].description.toString()
}
}
connectnet.cpp
#include "connectnet.h"
#include "stdio.h"
#include <QDebug>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QNetworkAccessManager>
#include <QUrl>
connectNet::connectNet(QObject *parent) : QObject(parent)
{
}
void connectNet::connectUrl(QString url)
{
QNetworkAccessManager *manager = new QNetworkAccessManager();
QNetworkRequest request;
QNetworkReply *reply = NULL;
request.setUrl(QUrl(url));
request.setRawHeader( "User-Agent" , "FAKE USER AGENT HERE" );
reply = manager->get(request);
connect(manager, SIGNAL(finished(QNetworkReply*)), this,
SLOT(replyFinished(QNetworkReply*)));
}
QString connectNet::replyFinished(QNetworkReply *reply)
{
return reply->readAll();
}
appname.cpp
#ifdef QT_QML_DEBUG
#include <QtQuick>
#endif
#include <sailfishapp.h>
#include "connectnet.h"
int main(int argc, char *argv[])
{
//INIT SETTINGS
QGuiApplication *app = SailfishApp::application(argc, argv);
QQuickView *view = SailfishApp::createView();
connectNet ConnectNet;
view->rootContext()->setContextProperty("connectNet", &ConnectNet);
view->setSource(SailfishApp::pathTo("qml/APPNAME.qml"));
view->showFullScreen();
app->exec();
}
Hope I've well explained what I'm looking for. Thanks for your help.
====================================================
EDIT 20/08/2015: added updated connectnet.h
#ifndef CONNECTNET_H
#define CONNECTNET_H
#include <QObject>
#include <QNetworkReply>
#include <QDebug>
#include <QNetworkRequest>
#include <QNetworkReply>
#include <QNetworkAccessManager>
#include <QUrl>
class ConnectNet : public QObject
{
Q_OBJECT
QNetworkAccessManager m_manager;
public:
ConnectNet(QObject * parent = 0) : QObject(parent) {
connect(&m_manager, &QNetworkAccessManager::finished,
[this](QNetworkReply * reply) {
if (reply->error() == QNetworkReply::NoError)
emit replyAvailable(QString::fromUtf8(reply->readAll()));
});
}
signals:
void replyAvailable(const QString & reply);
public slots:
void sendRequest(const QString url) {
QNetworkRequest request;
request.setUrl(QUrl(url));
request.setRawHeader("User-Agent", "MyLittleAgent");
m_manager.get(request);
}
};
#endif // CONNECTNET_H
this part of code gives a lot of errors :( (screenshot below)
connect(&m_manager, &QNetworkAccessManager::finished,
[this](QNetworkReply * reply) {
if (reply->error() == QNetworkReply::NoError)
emit replyAvailable(QString::fromUtf8(reply->readAll()));
});
compiling erros: http://i.stack.imgur.com/30vWn.jpg
Your problem is that you think synchronously. The connectUrl cannot return a value (and it doesn't), since when it runs the result is not available. What you must do, instead, is for the ConnectNet class to emit a signal when the data is available.
It'd be a horrible idea if you tried to make a synchronous wrapper that did return the value: the QML engine would be stuck as long as it took for the result to be received. You could freeze your application by pulling the network cable at the right moment, or if the server was down. Users hate that, and it's a horrible antipattern that must be expediently eliminated and discouraged.
Here's how your ConnectNet (please, not connectNet, lowercase names are for members!) class could look. Note that the QNetworkAccessManager instance doesn't need to be a pointer.
class ConnectNet : public QObject {
Q_OBJECT
QNetworkAccessManager m_manager;
public:
ConnectNet(QObject * parent = 0) : QObject(parent) {
connect(&m_manager, &QNetworkAccessManager::finished,
[this](QNetworkReply * reply) {
if (reply->error() == QNetworkReply::NoError)
emit replyAvailable(QString::fromUtf8(reply->readAll()));
});
}
Q_SLOT void sendRequest(const QString & url) {
auto request = QNetworkRequest(QUrl(url));
request.setRawHeader("User-Agent", "MyLittleAgent");
m_manager.get(request);
}
Q_SIGNAL void replyAvailable(const QString & reply);
};
Since connectNet instance instance is exposed as a property in the global QML context, you can connect to its signals as follows:
function getRequest() {
connectNet.sendRequest("http://myURL.com/index.php")
}
function resultHandler(result) {
var jsonResult = JSON.parse(result.toString())
lbOutput.text = jsonResult.predictions[0].description.toString()
}
Rectangle { // or any other item
Component.onCompleted: {
connectNet.replyAvailable.connect(resultHandler)
}
...
}
I tried declaring a signal in a prototype and then connecting it is script funcition for some reason it does not work as I hoped. My code is as follows. Could some one help me in this.
What I expected was, once I called p.setText('New String') in the script code, since setText emits the textChanged signal it should invoke the slot which is catchSignal(text) already connected in the script code.
Prototype header
#ifndef SCRIPTACTION_H
#define SCRIPTACTION_H
#include <QObject>
#include <QtScript>
class ScriptAction : public QObject , public QScriptable
{
Q_OBJECT
public:
ScriptAction(QObject *parent = 0);
signals:
void textChanged(const QString changedString);
};
#endif // SCRIPTACTION_H
Class
#include "scriptaction.h"
#include <QAction>
Q_DECLARE_METATYPE(QAction*)
ScriptAction::ScriptAction(QObject *parent) : QObject(parent)
{
}
Main Class
#include <QApplication>
#include <QDebug>
#include <QAction>
#include "scriptaction.h"
#include <QPushButton>
Q_DECLARE_METATYPE(QAction*)
QScriptValue qAction_Constructor(QScriptContext *ctx, QScriptEngine *eng)
{
qDebug() << "QAction is called";
if(ctx->isCalledAsConstructor())
{
QObject *parent = ctx->argument(0).toQObject();
QAction *action = new QAction("Test",parent);
return eng->newQObject(action, QScriptEngine::ScriptOwnership);
} else {
return QString("invalid call. Use new Constructor");
}
}
int main(int argc, char *argv[])
{
QApplication app(argc,argv);
QScriptEngine engine;
//Evaluating a simaple expresssion
qDebug() << engine.evaluate("1+2").toNumber();
QPushButton button;
QScriptValue buttonScript= engine.newQObject(&button);
engine.globalObject().setProperty("button", buttonScript);
engine.evaluate("button.text ='Hello Text'; button.show()");
//QAction Prototype
ScriptAction qsAction ;
QScriptValue script_proto = engine.newQObject(&qsAction);
engine.setDefaultPrototype(qMetaTypeId<QAction*>(), script_proto);
QScriptValue ctor = engine.newFunction(qAction_Constructor , script_proto);
QScriptValue metaObject = engine.newQMetaObject(&QObject::staticMetaObject, ctor);
engine.globalObject().setProperty("QSAction" , metaObject);
engine.evaluate("var p = new QSAction(button);p.textChanged.connect(catchSignal);");
engine.evaluate("function catchSignal(text) { print ('PROTOTYPE SIGNAL IS CALLED ',text); } p.setText('New String'); " );
return app.exec();
}
I got rid of the issue, and now I see the signal is being triggered and slot is called properly.
All I did was moving the code to a separate script file and start using the QScriptDebugger to see its output. Then I figured there was an error and the code is edited to work.
Anyone who wants an example prototype class, this will hopefully be a good guideline.
I know similar question to this have been asked, but I haven't found an answer that fixes my problem.
I'm adapting some existing Qt code to add server functionality to a program my company uses. To that end I added a QTcpServer object to the existing dialog, call listen() and connect a slot to the newConnection emitter, like:
.h
class QConsole : public QDialog
{
Q_OBJECT
public:
void init();
public slots:
void new_Connection();
private:
QTcpServer m_Server;
}
.cpp
void QConsole::init()
{
m_Server.listen(QHostAddress::Any, 12346);
QDialog::connect(&m_Server, SIGNAL(newConnection()), this, SLOT(new_Connection()));
}
Main is:
int main( int argc, char *argv[] )
{
QApplication app(argc, argv);
QConsole * _output_window = new QConsole(desktopRect);
_output_window->init();
_output_window->show();
return app.exec();
}
new_Connection() never gets called so I can't see the relevance, but here it is:
void QConsole::new_Connection()
{
}
This works fine in that my program starts listening on the port specified and if I telnet to it a connection of sorts it made, but new_Connection() is never ever ever called!
I've seen posts on this problem dating back to 2005 so it's obviously not a new thing, but what I haven't found is a satisfactory answer to the problem (or any answer actually). This has got everyone at work stumped, even the person that has written a Qt server program. I'm guessing that there is something fundamentally wrong with the existing framework, but I have no idea what it might be.
I have been tearing my hair out for a day and a half over this, and the closes I got to success was using waitForNewConnection() which would actually return me a socket, but when I connected to the readReady() emitter, that was never fired either. So what would prevent these signals never getting called?
Please spare my sanity and help me as much as you can.
Here is a complete working example, tested using MSVC++ 2010.
This listens for a connection on port 12346, replies with "HELLO WORLD" and logs the connection to a list on the dialog.
main.cpp
#include <QtGui>
#include "console.hpp"
int main(int argc, char** argv)
{
QApplication app(argc, argv);
Console con;
con.show();
return app.exec();
}
console.hpp
#include <QtCore>
#include <QtGui>
#include <QtNetwork>
class Console : public QDialog
{
Q_OBJECT
public:
Console();
public slots:
void connection();
private:
QTcpServer mServer;
QListWidget* mConnList;
};
console.cpp
#include "console.hpp"
Console::Console() :
QDialog(),
mServer(),
mConnList(new QListWidget())
{
if (!mServer.listen(QHostAddress::Any, 12346))
qDebug() << "Error during 'listen'" << mServer.errorString();
connect(&mServer, SIGNAL(newConnection()), this, SLOT(connection()));
QVBoxLayout* mainLayout = new QVBoxLayout();
mainLayout->addWidget(mConnList);
setLayout(mainLayout);
}
void Console::connection()
{
qDebug() << "CONNECTION";
QTcpSocket* skt = mServer.nextPendingConnection();
if (!skt)
return;
mConnList->addItem(QString("%1:%2").arg(skt->peerAddress().toString()).arg(skt->peerPort()));
skt->write("HELLO WORLD!\r\n");
skt->close();
}
test.pro
TEMPLATE=app
CONFIG+=console debug
QT=core gui network
HEADERS=console.hpp
SOURCES=main.cpp console.cpp
Another working example, again on Linux, although I have coded a program using QTcpServer to run on both Linux and Windows before without a problem. If this doesn't work, surely it must be either a Qt installation or OS configuration problem. Either that or a bug in the Qt version.
~/tcp_test$ qmake --version
QMake version 2.01a
Using Qt version 4.8.6 in /usr/lib/x86_64-linux-gnu
~/tcp_test$ for file in qconsole.{h,cpp} main.cpp tcp_test.pro ; do echo -e "$file:\n"; cat $file; echo; echo; done
qconsole.h:
#include <QDialog>
#include <QTcpServer>
class QConsole : public QDialog
{
Q_OBJECT
public:
QConsole();
public slots:
void connection();
private:
QTcpServer server;
};
qconsole.cpp:
#include "qconsole.h"
QConsole::QConsole()
{
server.listen(QHostAddress::Any, 12346);
QDialog::connect(&server, SIGNAL(newConnection()), this, SLOT(connection()));
}
void QConsole::connection()
{
qDebug("got connection");
}
main.cpp:
#include <QApplication>
#include "qconsole.h"
int main( int argc, char *argv[] )
{
QApplication app(argc, argv);
QConsole * window = new QConsole();
window->show();
return app.exec();
}
tcp_test.pro:
QT = core gui network
CONFIG += debug
TARGET = tcp_test
SOURCES = main.cpp qconsole.cpp
HEADERS = qconsole.h
~/tcp_test$ ./tcp_test &
[3] 9784
~/tcp_test$ nc localhost 12346
got connection
^C