Qt DoubleSpin Box value changed slot has called twice

Sowmiya R

I have created a sample application, it contains only QtdoubleSpinbox.
I have not overridden any methods.

below is my CPP code

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "qdebug.h"
#include <qspinbox.h>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{

    ui->setupUi(this);
    connect(ui->doubleSpinBox, SIGNAL(valueChanged(QString)), this, SLOT(on_doubleSpinBox_valueChanged1(QString)));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_doubleSpinBox_valueChanged1(const QString &arg1)
{
    qDebug()<<"doubleSpinBox value changed: "<<arg1;
}

mrjj

@Sowmiya-R
Must be something in your Qt/compiler I guess ??
Can you try this test
https://www.dropbox.com/s/9eftxqghndn2bhw/myspinbox.zip?dl=0

Vinod Kuntoji

@Sowmiya-R ,
Hi,
You can use Qt::UniqueConnection in Connect statement.

Sowmiya R

@mrjj

I have tested your code.

I am able to reproduce the same in debug mode.
Can you please put a break point in slot function and run it in debug mode and see.

mrjj

@Sowmiya-R
Ahh, now i see.
Yes the debugger seems to interfere with event loop so it does indeed call it twice on one click
if u place break point there. Else Not.

void MainWindow::on_doubleSpinBox_valueChanged(const QString &arg1)
{
   static int hmm=0;
    qDebug() << arg1;
    hmm++;
    qDebug() << hmm;
}

"1,00"
1
"2,00"
2

I would guess that pausing it triggers the repeat feature and since it dont get an mouse release event its why.

Sowmiya R

I have developed a application using Qt, there regardless of debug mode or release mode value changed slot has called twice only on spinbox box up/down controls.
I try to reproduce the same in sample application, but its happening only in debug mode.

There is something missing in my application. I will check it out.
Thank you guys for you suggestions.

mrjj

@Sowmiya-R

But it ONLY happens for me if i set break point.
Never, ever else.

Do it happen for you if yo have NO break points ?

Sowmiya R

@mrjj

yeah!

Without break point also its calling twice.

mrjj

@Sowmiya-R
Ok, that does not happen for me.
Without break point it works correctly here.

I have no idea what could be wrong with your Qt.

Since you are using a clean project to test, i assume is something with your pc or Qt.

Wael11

The double call to slot happened in my case only with a breakpoint in the slot function, otherwise it is called once only. The second call was triggered by a timer event

JonB

@Wael11
For anyone reading this: This is known behaviour, which I stumbled across a long time ago and it was infuriating.

With a QSpinbox Qt Internal code uses a timer on clicks/presses. If you step through in debugger you exceed the timeout and get bad/double behaviour.

Simplest: change all connect() to QSpinbox click/key to pass Qt::QueuedConnection as last parameter for connection type, not default Qt::DirectConnection. Now you can use debugger breakpoints and all will be well. I wrote a method to connect all my spinboxes like this.