[Development] Behaviour change in QML in Qt 5.8 regarding null

Thiago Macieira thiago.macieira at intel.com
Wed Sep 28 17:37:34 CEST 2016

On quarta-feira, 28 de setembro de 2016 08:54:10 PDT Simon Hausmann wrote:
> Hi,
> Ok, let me clarify: When the JavaScript engine wants to map a JS null value
> to a QVariant, it used to use
>     QVariant(QMetaType::VoidStar, (void *)0);
> and now uses
>     QVariant::fromValue(nullptr);

Neither is isNull() == true.

> If a string is to be converted to a QVariant, it will naturally use
> QVariant(thatString). I think if that
> string happens to be a null QString, then QVariant isNull() will return
> true, right?

Right. he question was whether QML strings were guaranteed to be non-null. If 
you can't guarantee that, then we can't rely on QVariant::isNull().

> If that is unsufficient for the pim code here (or generally any other code),
> then my recommendation
> would be to change the signature to take a QJSValue instead of a QVariant.
> The engine supports that
> transparently and the QJSValue API allows distinguishing between a
> JavaScript null and a string, etc.

Are we deprecating the QVariant interface?

Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center

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