[Qt-interest] QScript Newbie Question

[Sean Harmer]

Hi,

On Monday 08 February 2010 11:59:38 Alexander Carôt wrote:
> Hello Kent,
> 
> thanks for the reply ! However, my problem is possibly more "newby" than it
>  appears: I am still on 4.5.3, where the "bracket"-problem doesn't exist. I
>  simply wonder why my code actually does nothing:
> 
> I am connecting a line-edit-signal to the a script-slot as follows:
> 
> QScriptEngine engine;
> QLineEdit *edit = new QLineEdit("",this);
> edit->setGeometry(0,0,50,23);
> edit->show();
> QScriptValue handler = engine.evaluate("function (text){print('text was
>  changed to',text);}"); qScriptConnect(edit, SIGNAL(textChanged(const
>  QString &)), QScriptValue(), handler); qDebug() << handler.toString();
> 
> but whenever I type anything into the edit field nothing happens. I am
>  expecting the script to print the changed text into the terminal but
>  neither a text output nor an error message appears. Nevertheless, the last
>  qDebug-call plots the following into the terminal:
> 
> "function(text) {
>     print("text was changed to", text);
> }"
> 
> Since these are my first steps with QScript I am still unsure how to verify
>  this in order to achieve the desired script-print-action. Hence, any help
>  appreciated of course.

I may be being really dumb as I have only just scratched the surface of 
QtScript. However, I think that your QScriptEngine and QScriptValue objects 
could be going out of scope and getting destroyed. I think this because of the 
"this" pointer that you pass to the QLineEdit c'tor.

The following application works for me (Qt 4.6.1):

#include <QApplication>
#include <QDebug>
#include <QLineEdit>
#include <QScriptEngine>

int main( int argc, char* argv[] )
{
    QApplication app( argc, argv );

    QLineEdit* edit = new QLineEdit();
    edit->setGeometry( 0, 0, 150, 23 );
    edit->show();

    QScriptEngine engine;
    QScriptValue handler = engine.evaluate( "(function myFunc( text ) { print( 
'Text changed to:', text ); })" );
    qScriptConnect( edit, SIGNAL( textChanged( const QString& ) ), 
QScriptValue(), handler );
    qDebug() << handler.toString();  

    return app.exec();
}

To embed this within another object as will likely be the case, just create 
the QScriptEngine object on the heap so that it is not destroyed.

HTH,

Sean