C++ builder: How to convert TRectF to Variant

Question

I am using C++ Builder 10.2.3 (Rad Studio 10.2.3) I am trying to convert a TRectF to a Variant. But it seems not to be working:

• 1st Solution: using TValue::From(rect).AsVariant() or AsType(). I am getting the error message: Invalid Class TypeCast
• 2e Solution: Using TValue::Make() with ExtractRawData. But I cannot use it because __delphirtti() cannot work with TRectF.

This is an example of code from Qt I am trying to adapt:

void File::appendRects(const QList<QRectF> &rects)
{
    QList<QVariant> newRects = m_metadata["Rects"].toList();
    foreach (const QRectF &rect, rects)
        newRects.append(rect);
    m_metadata["Rects"] = newRects;
} 

The code line newRects.append(rect); adds a QRectF to a QVariant list. Which means that the conversion is done automatically.

Any solution which works?

Answer 1

TRectF is not a type that Variant supports natively, which is why your "solutions" do not work.

To store a TRectF in a Variant, you would have to either:

• store the TRectF data as a dynamic byte array, eg:

TRectF rect = ...;
int bounds[] = {0, sizeof(rect)-1}; 
Variant v = VarArrayCreate(EXISTINGARRAY(bounds), varByte);
// alternatively:
// Variant v = VarArrayCreate(OPENARRAY(int, (0, sizeof(rect)-1)), varByte);
void *p = VarArrayLock(v);
memcpy(p, &rect, sizeof(rect));
VarArrayUnlock(v);

• implement TCustomVariantType to represent the TRectF data inside a Variant, per Defining Custom Variants:

  By default, variants cannot hold values that are records, sets, static arrays, files, classes, class references, or pointers. You can, however, extend the Variant type to work with any particular example of these types. All you need to do is create a descendant of the TCustomVariantType class that indicates how the Variant type performs standard operations.

  But, be aware of this caveat:

  Note: C++ can use Custom Variant types, but TCustomVariantType descendants must be implemented in Delphi.