I am developing an TCP server application. I have the newDataReceived slot and I emit a signal in it like this:
void myclass::newDataReceived()
{
char data_received[1024] = {0};
client->read(data_received, client->bytesAvailable());
QString msg = data_received;
QString client_ip = client->peerAddress().toString();
emit dataReceived(msg,client_ip);
}
I have catched the signal from MainWindow, there is no problem. But, I have another class which is a QThread and I want this class to catch this signal too. But it does not do it. I connected the signal to my slot like,
srv_thread = new myclass();
connect(srv_thread, SIGNAL(dataReceived(QString,QString)), this, SLOT(incoming_message(QString,QString)));
What am I missing?
Thanks in advance!
Related
In the documentation of QTimer there is a Properties-section, containing the active-property.
This made me believe, there might be something like a activeChanged-signal, I could connect to.
For IMHO unapparent reasons
QObject::connect(m_timer, &QTimer::activeChanged, this, &MyObject::mySlot);
failes, stating activeChanged is no member of QTimer.
Basically, I want to do something, when the timer gets initially started (so not on restart) or finally stopped. When the signal activeChanged does not exist, has anyone knowledge:
Why it is a property at all?
If there are some other signals to connect to, to do this?
Any way to hook in, and do something when the timer is started or stopped?
test in main.cpp
QTimer* tim = new QTimer;
QObject::connect(tim, &QTimer::activeChanged, qApp, [tim](){qDebug() << "Active changed" << tim->isActive(); });
tim->start(40000); // I want to get a signal
tim->start(100); // I don't want to get a signal
tim->stop(); // I want to get a signal
Create your own timer class and encapsulate QTimer:
class Timer : public QObject
{
Q_OBJECT
QTimer m_timer;
public:
Timer ()
{
connect(&m_timer, &QTimer::timeout, this, &Timer::timeout);
}
void start(int msec)
{
if (m_timer.isActive())
{
// Restart detected -> block signal
m_timer.blockSignals(true);
m_timer.start(msec);
m_timer.blockSignals(false);
}
else
{
m_timer.start(msec);
}
}
}
Since the class Timer has the full control and knowledge of the QTimer, you can have any apparent behavior you want.
I am trying to connect mainwindow and dialog using signal and slot. I am very new to qt. I have a lineEdit and a pushButton in mainwindow.ui, a lineEdit in dialog.ui. And I have those very basic code:
mainwindow.h:
signals:
void sendString(QString);
mainwindow.cpp:
void MainWindow::on_pushButton_clicked()
{
Dialog *mDialog = new Dialog(this);
emit sendString(ui->lineEdit->text());
connect(this, SIGNAL(sendString(QString)), mDialog, SLOT(showString(QString)));
mDialog->show();
}
dialog.h:
private slots:
void showString(QString);
dialog.cpp:
void Dialog::showString(QString str)
{
ui->lineEdit->setText(str);
}
But after I clicked the pushButton, the dialog showed, but nothing changed in the lineEdit.I hope I explain this clearly enough?
Can someone explain to me why and how to solve this? Thanks.
emit signal after connect
void MainWindow::on_pushButton_clicked()
{
Dialog *mDialog = new Dialog(this);
connect(this, SIGNAL(sendString(QString)), mDialog, SLOT(showString(QString)));
mDialog->show();
emit sendString(ui->lineEdit->text());
}
You have to create the connection before the emit.
But in your case you dont need the signal of the of the mainwindow at all. You invoke the showString method directly.
I am trying to put the data passed to a mainwindow.cpp function on the screen with the typical ui->control->setText(message) without success. The same line works if it is in a timer loop or a button function but not from display_that_data function
"MainWindow::display_that_data()" is called from myudp.cpp with the following lines
MainWindow show_tlm;
show_tlm.display_that_data(data_source, buf_copy);
mainwindow.cpp (updated to include emitting a signal for a SIGNAL/SLOT connection)
The SIGNAL/SLOT connection is set up in the constructor with the following line
connect (this, SIGNAL (showdata_signal()), this, SLOT(showdata_slot()));
void MainWindow::display_that_data(QByteArray data_source, QByteArray tlmBuf){
QString msg ;
msg = " in display_that_data";
qDebug() << msg ;
ui->tlm_vals->setText(msg);
//generate a signal which will trigger showdata_slot
emit showdata_signal();
msg = " in display_that_data after emit showdata_signal()";
qDebug() << msg ;
}
void MainWindow::showdata_slot() {
QString msg = "showdata_slot called";
qDebug() << msg ;
ui->tlm_vals->setText(msg);
}
Runtime debug messages show that code is making it to the showdata_slot but it is still not writing to the ui->tlm_vals
" in display_that_data"
"showdata_slot called"
" in display_that_data after emit showdata_signal()"
but.... neither one of the ui->tlm_vals->setText(msg) lines are putting text on the ui
"MainWindow::realtimeDataSlot()" is called by at timer timout signal as follows:
void MainWindow::setupRealtimeDataDemo(QCustomPlot *customPlot) {
// setup a timer that repeatedly calls MainWindow::realtimeDataSlot
connect(&dataTimer, SIGNAL(timeout()), this, SLOT(realtimeDataSlot()));
dataTimer.start(1000);
}
void MainWindow::realtimeDataSlot(){
QString temp = QString("%1").arg(epochTime, 10, 10, QChar('0'));
ui->tlm_vals->setText(temp);
}
And this works perfectly (of course I have to disable it to see if showdata_slot is writing to the ui)
I thought the problem was a needed SIGNAL and SLOT connection to trigger the write to the ui but generating a SIGNAL/SLOT connection (which debug shows as working) still does not write to the ui from the slot function.
For completeness mainwindow.h contains the following
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
void setupRealtimeDataDemo(QCustomPlot *customPlot);
void display_that_data (QByteArray data_source, QByteArray tlmBuf);
private slots:
void realtimeDataSlot();
void showdata_slot();
private:
Ui::MainWindow *ui;
QTimer dataTimer;
What am I missing/doing wrong?
Somewhere deeply embedded in Qt there is a difference between gui mouse click generated event and code generated event and this somehow caues Qt behavior to vary with the same lines of code. I will repost a more more "root level" question on this topic.
I am using RtMidi library to handle midi message in my Qt application and I am facing problem with slot trigger:
My PhMidiInput object is emiting signal from the RtMidi callback upon specific midi message but the slots are not always triggered.
Here is a part of the PhMidiInput class:
class PhMidiInput : QObject
{
Q_OBJECT
public:
void PhMidiInput() {}
signals:
void quarterFrame(unsigned char data);
private:
static void callback(double, std::vector< unsigned char > *message, void *userData ) {
PhMidiInput *midiInput = (PhMidiInput*)userData;
if(midiInput)
midiInput->onMessage(message);
}
void onMessage(std::vector<unsigned char> *message) {
...
emit quarterFrame(data);
...
}
}
Connecting to a lambda functor works:
PhMidiInput midiIn;
int quarterFrameCount;
connect(&midiIn, &PhMidiInput::quarterFrame, [&](unsigned char data) {
quarterFrameCount++;
});
Connecting to my application window works to:
// MyWindow inherits from QMainWindow
connect(_midiIn, &PhMidiInput::quarterFrame, this, &MyWindow::onQuarterFrame);
When trying to connect to a custom class (MidiTest) inheriting from QObject it does'nt trigger:
connect(_midiIn, &PhMidiInput::quarterFrame, this, &MidiTest::onQuarterFrame);
I was wondering if there was something around QObject::moveToThread() but since I don't create the thread myself (the signal is sent from a callback) I don't know if I need to use it or not.
It is as simple as calling emit obj->quarterFrame(data); from the callback. If the connection type is default then this will be perfectly thread safe.
Though you should create a QByteArray from data to pass around as data will likely not be valid by the time the slots get called.
void callback(..., void* user){
//user is the standard void* in most callbacks passed as reinterpret_cast<void*>(this)
unsigned char* data = ...;
QByteArray bytes(data);
emit reinterpret_cast<PhMidiInput>(user)->quarterFrame(bytes);//calling the signal which will behave as you'd expect
}
In the last connect() call you pass this and MidiTest::onQuarterFrame as the receiver object and method. I bet this is not an instance of MidiTest, is it?
The problem here is that you're passing SLOT method from MidiTest, while the receiver object is this, which is not instance of MidiTest. Change receiver from this to some instance of MidiTest.
I'm surprised this code doesn't crash your application when running.
I have a class looking like this:
class FakeRunner : public QObject
{
Q_OBJECT
private:
QProcess* proc;
public:
FakeRunner();
int run()
{
if (proc)
return -1;
proc = new QProcess();
QStringList args;
QString programName = "fake.exe";
connect(comp, SIGNAL(started()), this, SLOT(procStarted()));
connect(comp, SIGNAL(error(QProcess::ProcessError)), this,
SLOT(procError(QProcess::ProcessError)));
connect(comp, SIGNAL(finished(int, QProcess::ExitStatus)), this,
SLOT(procFinished(int, QProcess::ExitStatus)));
proc->start(programName, args);
return 0;
};
private slots:
void procStarted() {};
void procFinished(int, QProcess::ExitStatus) {};
void procError(QProcess::ProcessError);
}
Since "fake.exe" does not exist on my system, proc emits the error() signal. If I handle it like following, my program crashes:
void FakeRunner::procError(QProcess::ProcessError rc)
{
delete proc;
proc = 0;
}
It works well, though, if I don't delete the pointer. So, the question is how (and when) should I delete the pointer to QProcess? I believe I have to delete it to avoid a memory leak. FakeRunner::run() can be invoked many times, so the leak, if there is one, will grow.
Thanks!
You can't delete QObject instance inside slot which is connected to a signal in this instance using normal delete operator. This is due to the fact that if signal and slot connected using direct connection then the slot actually called from the signal implementation made by moc. This is like attempt to delete this; from inside the member of a class. There is a solution QObject::deleteLater(). Object will be deleted by Qt event loop inside events processing function. So you need to call proc->deleteLater() in your case.
And you don't need to disconnect signal from slot since Qt do it automatically when QObject is deleted.