QLineEdit and QComboBox have unrelated behavior - c++11

Question

I have a user interface with a lot of controls. However I have a problem with a QLineEdit and a QComboBox that are not responding properly.
I am basically converting from pixel measurements to millimeters/centimeters/decimeters and meters with a QComboBox and showing the result on a QLineEdit.
For the conversion table I used this page.
When I choose fromPixelToMillimeters() it does the conversion, but when I choose fromPixelToCentimeters() I think it is using the present value after the first conversion of fromPixelToMillimeters(). And if I go back choosing fromPixelToMillimeters() I get a different result too. This happens continuously, I get different measures each time.
See the code below:
void MainWindow::on_cBoxMeasures_currentIndexChanged(const QString &arg1)
{
if(arg1 == "Select Conversion(s)") {
return ui->leftLineEditDist->setText(QString("%1").arg(ui->leftLineEditDist->text().toDouble()));
} else if(arg1 == "pixel") {
return ui->leftLineEditDist->setText(QString("%1").arg(ui->leftLineEditDist->text().toDouble()));
} else if(arg1 == "mm") {
return fromPixelToMillimeters();
} else if(arg1 == "dm") {
return fromPixelToDecimeters();
} else if(arg1 == "cm") {
return fromPixelToCentimeters();
} else if(arg1 == "m") {
return fromPixelToMeters();
}
}
void MainWindow::fromPixelToMillimeters()
{
double mm = ui->leftLineEditDist->text().toDouble();
double dpi = 300;
double totalDistanceInMillimeter = (mm*25.4)/dpi;
ui->leftLineEditDist->setText(QString("%1").arg(totalDistanceInMillimeter));
ui->leftLineEditDist->show();
}
void MainWindow::fromPixelToCentimeters()
{
double mm = ui->leftLineEditDist->text().toDouble();
double dpi = 300;
double totalDistanceInCm = ((mm*25.4)/dpi)*0.1;
ui->leftLineEditDist->setText(QString("%1").arg(totalDistanceInCm));
ui->leftLineEditDist->show();
}
void MainWindow::fromPixelToDecimeters()
{
double mm = ui->leftLineEditDist->text().toDouble();
double dpi = 300;
double totalDistanceInDcm = ((mm*25.4)/dpi)*0.01;
ui->leftLineEditDist->setText(QString("%1").arg(totalDistanceInDcm));
ui->leftLineEditDist->show();
}
void MainWindow::fromPixelToMeters()
{
double mm = ui->leftLineEditDist->text().toDouble();
double dpi = 300;
double totalDistanceInM = ((mm*25.4)/dpi)*0.001;
ui->leftLineEditDist->setText(QString("%1").arg(totalDistanceInM));
ui->leftLineEditDist->show();
}
void MainWindow::on_cBoxMeasures_currentIndexChanged(int index)
{
switch (index) {
case(0):
break;
case(1):
break;
case(2):
fromPixelToMillimeters();
break;
case(3):
fromPixelToCentimeters();
break;
case(4):
fromPixelToDecimeters();
break;
case(5):
fromPixelToMeters();
break;
}
}
Please advise on what the problem might be.

Answer 1

I think these slots
on_cBoxMeasures_currentIndexChanged(const QString &arg1)
on_cBoxMeasures_currentIndexChanged(int index)
are connected the onIndexChange signal.
When the combo value will be changed, these two slots will be called simultaneously.
So that your code wont work well.
I recommend you to remove one of these slots.