[PyQt] Inconsistent behavior with multiple inheritance and ConvertToSubClassCode

[Phil Thompson]

On 25 Sep 2018, at 8:10 am, Nyall Dawson <nyall.dawson at gmail.com> wrote:
> 
> Hi list,
> 
> I've been struggling for a while with some inconsistent behavior
> relating to ConvertToSubClassCode and a multiple inherited class.
> 
> The definition currently looks something like:
> 
> 
> class LayoutItem : LayoutObject, QGraphicsRectItem
> {
> %TypeHeaderCode
> #include "layoutitem.h"
> #include "layoutitempicture.h"
> #include "layoutitemlabel.h"
> %End
> %ConvertToSubClassCode
>    // the conversions have to be static, because they're using
> multiple inheritance
>    // (seen in PyQt4 .sip files for some QGraphicsItem classes)
>    switch ( sipCpp->type() )
>    {
>      case QGraphicsItem::UserType + 104:
>        sipType = sipType_LayoutItemPicture;
>        *sipCppRet = static_cast<LayoutItemPicture *>( sipCpp );
>        break;
>      case QGraphicsItem::UserType + 105:
>        sipType = sipType_LayoutItemLabel;
>        *sipCppRet = static_cast<LayoutItemLabel *>( sipCpp );
>        break;
>      default:
>        sipType = 0;
>    }
> %End
>  public:
>     ...
> 
> 
> While this... sometimes... works correctly, most often LayoutItem
> subclasses are not automatically cast to the subclass, and remain as
> LayoutItems only. Is the ConvertToSubClassCode incorrect here?

There is nothing obviously wrong. You probably need to put in debug statements to work out exactly what is happening.

Phil