[Interest] QObject-derived default property read-only

[Brian Dentino]

Thanks for the suggestion, Marian.

It turns out the problem was that not all of the classes in my hierarchy were registered with qml. The type within the QQmlListProperty was a subclass of another custom QObject-derived type which I didn't register because it's an abstract class. But registering it as an uncreatable-type did the trick and got rid of the "read-only" errors.

Brian

On Oct 13, 2014, at 2:33 AM, Marian Beermann <public at enkore.de> wrote:

> The QQmlListProperty you return from attachments() doesn't have an
> AppendFunction I guess? You need all four operations (Count, At, Clear,
> Append) defined on a list property that's also a default property.
> 
> The "backing store" is usually owned by the object the property belongs
> to, which is the most convenient solution, as it must remain valid as
> long as the property can be accessed.
> 
> On 13.10.2014 03:33, Brian Dentino wrote:
>> I'm working on a qml plugin in which I register a QObject-derived type
>> for use within qml. I've set the default property on this item to be a
>> QQmlListProperty<(other qobject derived type)>, and I've setup a READ
>> function for this property. For some reason the qml engine will not load
>> my application, complaining that this default property is read-only. 
>> 
>> I understand you typically have to define a WRITE function in order to
>> make properties writeable from qml, but the example that comes with Qt
>> regarding default properties does not do this, and it compiles fine:
>> http://qt-project.org/doc/qt-5/qtqml-referenceexamples-default-example.html
>> 
>> Here's the class definition I'm using:
>> 
>> class DefaultContent : public QObject
>> 
>> {
>> 
>>    Q_OBJECT
>> 
>> 
>>    Q_PROPERTY(QQmlListProperty<ShareableItem> attachments READ attachments)
>> 
>>    Q_CLASSINFO("DefaultProperty", "attachments")
>> 
>> 
>> public:
>> 
>>    explicit DefaultContent(QObject* parent = 0);
>> 
>> 
>>    QQmlListProperty<ShareableItem> attachments();
>> 
>> 
>> signals:
>> 
>> 
>> public slots:
>> 
>> 
>> private:
>> 
>>    QList<ShareableItem*> m_attachments;
>> 
>> 
>> };
>> 
>> 
>> And the qml...
>> 
>> *import* QtQuick.2.2
>> *import* QtQuick.Window 2.1
>> *import* Qtino.SharingKit 1.0 //This is my plugin that registers
>> 'DefaultContent'
>> 
>> Window {
>> 
>>    DefaultContent {
>> 
>>        id: defaultContentItem
>> 
>>        ImageItem { source: rootScreenGrab.url }
>> 
>>    }
>> 
>> }
>> 
>> 
>> The error I get is "Invalid property assignment: "attachments" is a read-only property"
>> 
>> 
>> Am I doing something obviously wrong here? If I absolutely must have a
>> WRITE method on this property, how would that work with a
>> QQmlListProperty type if the backing model is a QList? Would the list be
>> owned by js or cpp? And how is that the provided Qt example can work
>> without a WRITE method?
>> 
>> Any help would be much appreciated,
>> Brian
>> 
>> 
>> 
>> 
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