Den 25. mai 2012 02:35, skrev ext [email protected]:
> Hi,
>
>>> In QtQuick 2.0 (ie, Qt 5.0), we are thinking about using property var
>>> more often in the implementation (eg, of qobject-derived-type
>>> properties) to avoid some of those edge-cases, and providing more
>>> consistent (and useful) referencing semantics.
>> Can you say what 'var' is and why it would help?
> In QtQuick 1.x, you could not define a "JavaScript var-type property" in a
> QML item. The closest thing provided was "property variant" which,
> internally, is a QVariant. Assigning a JavaScript object to that property
> would result in it being converted to a QVariantMap. Accessing that property
> from JS would result in that QVariantMap being converted back into a JS
> object. You could not store a JS function reference, or any other "special"
> JS value in a "property variant" property (eg, null, undefined).
>
> In QtQuick 2.0, we deprecated "property variant" and added "property var".
> Internally, "property var" properties are JS values. Thus, you can store
> anything created in JS, including JS function references. This allows
> greater dynamicity and flexibility. Only when you access that property from
> C++ (via QObject::property() or QQmlProperty::read()) will it be converted to
> a QVariant (following the same conversion rules as for any other JS value to
> QVariant conversion).
>
Also note that when you implement types on the C++ side, you can use the
QJSValue class as a property or method parameter to transfer values
between C++ and QML/JS without type/data loss. This also includes JS
functions; for example, you can assign a function to a property from QML
and call it later from C++ using QJSValue::call().
There's also QJson{Value,Object,Array} integration.
Best regards,
Kent
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