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.