Cyclic call between 2 QLineEdit and signals

[MaxiARG]

Hi guys, first post here.
I just did a simple km/h to m/s conversor. 2 QLineEdit triggered with textChanged. "calculadora" just means calculator. The problem is that when i write something in the left box, it triggers another event in the right box, then enters an infinite loop of signal calls. How should i avoid this?

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    calculadora= new Calculadora(ui->lineEdit_Kms, ui->lineEdit_ms);

    QObject::connect(ui->lineEdit_Kms,SIGNAL(textChanged(QString)),
                     calculadora, SLOT(kms2ms(QString))
                     );
    QObject::connect(ui->lineEdit_ms,SIGNAL(textChanged(QString)),
                     calculadora, SLOT(ms2kms(QString))
                     );
}

Calculadora::Calculadora(QLineEdit *_kms,QLineEdit *_ms){
    kms=_kms;
    ms=_ms;
}

void Calculadora::kms2ms(QString val)
{
   double res= val.toDouble()*3.6f;
   QString texto= QString::number(res);

   ms->setText("");
   ms->insert(texto);
}

void Calculadora::ms2kms(QString val)
{
     float div=0.27f;
    double res= val.toDouble()*div;
    QString texto= QString::number(res);
    kms->setText("");
    kms->insert(texto);
}

[mpergand]

Hi,

That's normal, when you do setText() on the second LineEdit, the signal is emitted.

Two options:

• call blockSignals(true) on the second LineEdit before setText and again with false. (never used this method, hopes it's work ...)
• use a Button and update the LineEdits when the user clicks it.

[EDIT] A better idea would be to use returnPressed() signal.

[aha_1980]

@MaxiARG: You can just use the textEdited(QString) signal instead textChanged and it should work.

[SGaist]

Hi and welcome to devnet,

To add to my fellows, why do you call setText and then insert ? Why not directly setText(texto) ?

On a side note, you should use const QString &val as slot parameters. That will avoid useless copies.

[MaxiARG]

@SGaist Thanks SGaist! it was my first 24 hours of QT so i am like a big sponge absorving lots of knowledge like yours. i really apreciate your sugestion. I will use const QString &val from now on i just wanted to keep it simple, but i will investigate ir further. At the other hand, when i tried to set a double or a float value to the QEditLine, it printed "inf" or really big numbers and thats why i splited a method that i could have done in 1 line, in 5 lines. this part was tricky.
After a couple of minutes i succed but i left the code just like that, without properly refactoring it hehe. Many thanks for your reply!

   double res= val.toDouble()*3.6f;
   QString texto= QString::number(res);
   ms->setText("");
   ms->insert(texto);

[MaxiARG]

@mpergand Many thanks mpergand! my first 24 hours with QT was a succed! i will try both options just to check how it works! many thanks again!

[MaxiARG]

@aha_1980 Many thanks sir! textEdited together with setText was a quick solution. i had to replace insert for setText. aparently insert emmits textEdited so i had to replace that sentence too. Many thanks!

[SGaist]

Again, remove the insert line and change the setText call to setText(texto). You'll avoid useless operations and your code will be cleaner.