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Thread: ActiveQt : Setting Currency properties of a QAxObject

  1. #1
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    Default ActiveQt : Setting Currency properties of a QAxObject

    I'm accessing some third-party COM objects that have Currency/Decimal properties. ActiveQt supports the Currency (CY) type of COM, which is simply an int64, using qlonglong. For instance, an amount of $1.23 is saved as 12300. Reading such a currency property in a QAxObject is not a problem -- I simply divide by 10000 to get the real amount. However, setting such a property is a problem since the input is taken "at face value". Floating point numbers are converted to qlonglongs and cents are omitted in the conversion:
    Qt Code:
    1. double value1 = 1.23;
    2. qaxobject->setProperty("Amount", value1);
    3. // property("Amount") returns 10000 = $1
    4.  
    5. // Multiplying by 10,000 beforehand therefore doesn't work either
    6. qlonglong value2 = 12300; // trying again for $1.23
    7. qaxobject->setProperty("Amount", value2);
    8. // property("Amount") returns 123000000 = $12300
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    Is this because of the conversion to QVariant? If so, does anybody know a way around setProperty/dynamicCall to set the property in its native type? Or are the third-party components at fault? Thanks a lot.
    (Using Qt4.8.2, Visual Studio 2010)

  2. #2
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    Default Re: ActiveQt : Setting Currency properties of a QAxObject

    Try:
    Qt Code:
    1. qlonglong value2 = 12300;
    2. qaxobject->setProperty("Amount", QVariant(value2));
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    I suspect you are getting a QVariant(int) (because the value will fit) instead of QVariant(qlonglong) inside the ActiveQt marhsalling code which then fails to match it to the CY field properly.

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    Default Re: ActiveQt : Setting Currency properties of a QAxObject

    I tried that. Unfortunately, it still returns 123000000.

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    Default Re: ActiveQt : Setting Currency properties of a QAxObject

    Digging a bit deeper, I found the following in Qt's qaxtypes.cpp, in the method QVariantToVARIANT(..., bool out = false). QVariantToVARIANT is used by QAxBase in its method internalProperty to convert QVariants to the Microsoft VARIANT format when setting properties.
    Qt Code:
    1. case QVariant::LongLong:
    2. // arg.vt is set by QAxBase to VT_ERROR and out == false, so the first two if-cases are skipped
    3. if (out && arg.vt == (VT_CY|VT_BYREF)) {
    4. arg.pcyVal->int64 = qvar.toLongLong();
    5. // this checks for VisualStudio 2005 or higher
    6. #if !defined(Q_OS_WINCE) && defined(_MSC_VER) && _MSC_VER >= 1400
    7. } else if (out && arg.vt == (VT_I8|VT_BYREF)) {
    8. *arg.pllVal = qvar.toLongLong();
    9. } else {
    10. arg.vt = VT_I8; // method jumps here because I use VisualStudio 2010 on Win7Pro
    11. arg.llVal = qvar.toLongLong(); // here it sets an integer value, not a currency value
    12. if (out) {
    13. arg.pllVal = new LONGLONG(arg.llVal);
    14. arg.vt |= VT_BYREF;
    15. }
    16. }
    17. #else
    18. } else {
    19. arg.vt = VT_CY; // if it jumped here everything would be fine.
    20. arg.cyVal.int64 = qvar.toLongLong();
    21. if (out) {
    22. arg.pcyVal = new CY(arg.cyVal);
    23. arg.vt |= VT_BYREF;
    24. }
    25. }
    26. #endif
    27. break;
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    Why does it check for _MSC_VER >= 1400 (Visual Studio 2005)? If I used something older or no VisualStudio at all, then there wouldn't be a problem. This basically removes support for the Currency type from VisualStudio/Qt.

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    Default Re: ActiveQt : Setting Currency properties of a QAxObject

    This might seem familiar: https://bugreports.qt-project.org/browse/QTBUG-3828

    Why do you think arg.vt == VT_ERROR? That seems an odd thing.

  6. The following user says thank you to ChrisW67 for this useful post:

    drfitz (27th July 2012)

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    Default Re: ActiveQt : Setting Currency properties of a QAxObject

    Thanks for the link. We were about to write a Qt bug report. Good to know it's been hanging around there since 2009. Well, we'll probably have write our own fix if they don't.
    Quote Originally Posted by ChrisW67 View Post
    Why do you think arg.vt == VT_ERROR? That seems an odd thing.
    It's just an initial value. This is what QAxBase does when it calls the method:
    Qt Code:
    1. int QAxBase::internalProperty(QMetaObject::Call call, int index, void **v)
    2. {
    3. ....
    4. case QMetaObject::WriteProperty:
    5. {
    6. .....
    7. arg.vt = VT_ERROR;
    8. .....
    9. QVariantToVARIANT(qvar, arg, proptype);
    10. if (arg.vt == VT_EMPTY || arg.vt == VT_ERROR) {
    11. qWarning("QAxBase::setProperty: Unhandled property type %s", prop.typeName());
    12. break;
    13. }
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