Convert between a custom data type wrapped in a QVariant

[darkadept]

I have a custom class called Money that I want stored in a QVariant. I then want to take that QVariant and convert it to and from a QVariant of type double.

Here is my custom Money class:

class Money {
public:
  Money(double value = 0.00) {
    _val = value;
  }
  ~Money() { }
  double toDouble() {
    return _val;
  }
  operator Double() {
    return toDouble();
  }
private:
  double _val;
};
 
Q_DECLARE_METATYPE(Money);

class Money {
public:
  Money(double value = 0.00) {
    _val = value;
  }
  ~Money() { }
  double toDouble() {
    return _val;
  }
  operator Double() {
    return toDouble();
  }
private:
  double _val;
};

Q_DECLARE_METATYPE(Money);

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I'm using Qt's property system (which stores QVariants) but I'll just simplify everything here:

//Create a QVariant of type double
double myDouble = 2.345;
QVariant doubleVariant;
doubleVariant.setValue(myDouble);
 
//Create a QVariant of type Money
QVariant moneyVariant;
moneyVariant.setValue(Money(0.00));
 
/*This is where I'm bogged down. 
I have a QVariant of type double that holds the real value. 
I also have an empty QVariant of type Money. 
I want to be able to transfer the value from doubleVariant to
moneyVariant without knowing about the Money class or double type.
I also want to preserve what type the destination QVariant is.*/
 
//Attempt to convert from the double variant to the money variant
moneyVariant = QVariant::fromValue(doubleVariant);
Money myMoneyValue = moneyVariant.value<Money>();
 
//Obviously the above two lines doesn't work. 
//Instead of moneyVariant being a QVariant of type Money it is now
//a QVariant of type double. Also the conversion back to Money doesn't work.

//Create a QVariant of type double
double myDouble = 2.345;
QVariant doubleVariant;
doubleVariant.setValue(myDouble);

//Create a QVariant of type Money
QVariant moneyVariant;
moneyVariant.setValue(Money(0.00));

/*This is where I'm bogged down. 
I have a QVariant of type double that holds the real value. 
I also have an empty QVariant of type Money. 
I want to be able to transfer the value from doubleVariant to
moneyVariant without knowing about the Money class or double type.
I also want to preserve what type the destination QVariant is.*/

//Attempt to convert from the double variant to the money variant
moneyVariant = QVariant::fromValue(doubleVariant);
Money myMoneyValue = moneyVariant.value<Money>();

//Obviously the above two lines doesn't work. 
//Instead of moneyVariant being a QVariant of type Money it is now
//a QVariant of type double. Also the conversion back to Money doesn't work.

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Any ideas? I will try to clarify what I'm trying to do if that doesn't make sense.

Thanks,
Mike

[wysota]

I don't think this is possible. If your Money structure is equivalent to double, why not use double in the first place?

[pckoster]

Shouldn't you register it first with a call to qRegisterMetaType (http://doc.trolltech.com/4.1/qmetaty...gisterMetaType)

What are the results of calls to canConvert() and convert() or toDouble() functions?