Qt Script function wrapping - qt

Question

I am going through the documentation of Qt Scripting and came up to it is totally confusing and full if mis guiding text. Could some please explain in simple English how to wrap a function and access it in script code after wrapping. I have included my example below.
Wrapper function. This is a simple wrapper which I need to return the string that is passed as the parameter. following is the code.
#include <QApplication>
#include <QtScript/QScriptEngine>
#include <QtScript/QScriptContext>
#include <QDebug>
QScriptValue returnProperty(QScriptContext *context , QScriptEngine *engine)
{
qDebug() << "running returnValues Function "<< context->argument(0).toString();
return context->thisObject().property("returnValue");
}
int main(int argc, char *argv[])
{
QApplication app(argc,argv);
QScriptEngine engine;
//Evaluating a simple expression
qDebug() << engine.evaluate("1+2").toNumber();
QScriptValue func = engine.globalObject();
func.setProperty("foo",engine.newFunction(returnProperty),QScriptValue::PropertyGetter);
engine.evaluate("var v= foo('name') ; print( 'This prints values from addValues function :',v) ;");
}
And the output is as follows
3
Running returnValues Function "undefined"
If I am understanding this correctly this is what I should do and if I call engine.newObject() as it is mentioned in the doc function does not even get called.
what I do not get here is that in what is the property I am assigning in func.setproperty line and what can I do with the property foo once I set it. How can I set a value in the function.
I appreciate if someone explain what I am doing wrong here.

Answer 1

You are already on the right track. QScriptEngine::newFunction() brings the function into the engine. Now, you need a way to access this function from the script. A "function" is just a property of the global object and you can add a new property with setProperty(). The code
QScriptValue globalObject = engine.globalObject();
QScriptValue func = engine.newFunction(returnProperty);
globalObject.setProperty("foo", func);
produces the output
3
running returnValues Function "name"
This prints values from addValues function : name
The flags QScriptValue::PropertyGetter and QScriptValue::PropertySetter are only needed, when you want to create a property, which has to call a function upon access. It is similar to the properties of QObject. Consider this example:
class MyObject : public QObject
{
Q_PROPERTY(QString name READ getName WRITE setName)
};
MyObject* obj = new MyObject;
When you do a obj->setProperty("name", "Sam"); you call MyObject::setName("Sam") in the background and obj->getProperty("name") is a wrapper for MyObject::getName(). A small example:
QScriptValue getName(QScriptContext* ctx, QScriptEngine* eng)
{
// Return the value of the internal '_name_' property.
qDebug() << "Getter 'getName' called";
return ctx->thisObject().property("_name_");
}
QScriptValue setName(QScriptContext* ctx, QScriptEngine* eng)
{
// Do some processing and store the name in an internal '_name_' property.
qDebug() << "Setter 'setName' called";
ctx->thisObject().setProperty("_name_",
ctx->argument(0).toString().toUpper());
return QScriptValue::UndefinedValue;
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QScriptEngine engine;
QScriptValue globalObject = engine.globalObject();
// Create a new object.
QScriptValue obj = engine.newObject();
// Bring the functions into the engine.
QScriptValue getNameFunc = engine.newFunction(getName);
QScriptValue setNameFunc = engine.newFunction(setName);
// Create a 'name' property, which calls the getter and setter from above.
obj.setProperty("name", getNameFunc, QScriptValue::PropertyGetter);
obj.setProperty("name", setNameFunc, QScriptValue::PropertySetter);
// Make the new object known as 'person'.
globalObject.setProperty("person", obj);
// Test our construct.
engine.evaluate("print('Set the name to fitzgerald');");
engine.evaluate("person.name = 'fitzgerald';");
engine.evaluate("print('And the name is... ' + person.name)");
}
Finally the output:
Set the name to fitzgerald
Setter 'setName' called
Getter 'getName' called
And the name is... FITZGERALD