QQmlListProperty constructor doesn't accept my arguments

themts

Hi,

I'm doing my first steps with QQmlListProperty.
Unfortunately I'm not able to create such list :-(

header:

class TestClass : public QQuickFramebufferObject    
{
    Q_OBJECT
    Q_PROPERTY(QQmlListProperty<TestItem> lstTestItems READ lstTestItems)

private:
    static int count_lstTestItems(QQmlListProperty<TestItem> *list);
    static TestItem* at_lstTestItems(QQmlListProperty<TestItem> *list, int index);

public:
    QQmlListProperty<TestItem> lstTestItems() const;
}

source:

QQmlListProperty<TestItem> TestClass::lstTestItems() const
{              
    return QQmlListProperty<TestItem>(this, 0, &TestClass::count_lstTestItems, &TestClass::at_lstTestItems);
}

Error:
error: C2665: "QQmlListProperty<TestItem>::QQmlListProperty": Durch keine der 5 Überladungen konnten alle Argumenttypen konvertiert werden.

What am I missing here?

Thanks!
mts

P.S. how can I mark parts of my post as code?

[edit: Added missing coding tags three back sticks to start and three to end SGaist]

dasRicardo

OK, i did nearly the same as you here an working example.

// declare
Q_PROPERTY(QQmlListProperty<QObject> fields READ fields)
//getter
QQmlListProperty<QObject> fields();
//member to fill with data
QList<QObject*> m_fields;

//implementation of the getter
QQmlListProperty<Object> YourClass::fields() {
        return QQmlListProperty<Object>(this, this->m_fields);
      }

Thats all for me. I have to replace MyCustomClass with QObject but my custom class derived from QObject this is needed see documentation of QQmlListProperty

[edit: updated coding tags SGaist]

themts

@SGaist: Thanks

@dasRicardo:
so you say I have to replace

QQmlListProperty<TestItem>

with

QQmlListProperty<QObject>

even if TestItem is derived from QObject? Why?

mts

dasRicardo

Hmm,

my biggest misstake was my CustomClass have a namespace so if you use namespace also u need to do this:

Q_PROPERTY(QQmlListPropertyfull::namespace::CustomClass fields READ fields)

themts

I don't use a namespace in my class.

dasRicardo

No i dont want to say u need to replace your custom class with QObject sorry my english is horrible. I did this for this example because in my production code i have to use my custom class so this doesn't make sense here to post.

Not enough info to help you, i doesn't know how your TestItem class looks like

themts

TestItemClass:

class TestItem : public NChartRenderItem
{
    Q_OBJECT    
private:
    QOpenGLBuffer *m_vertexBuffer = NULL;

public:
    TestItem();
    ~TestItem();

    // NChartRenderItem interface
public:
    bool createVertexBuffer(int bufferSize);
    bool renderItem();
};

NChartRenderItem-Class:

class NChartRenderItem : public QObject
{
    Q_OBJECT
public:
    explicit NChartRenderItem(QObject *parent = 0);
    ~NChartRenderItem();

    virtual bool createVertexBuffer(int bufferSize) = 0;
    virtual bool renderItem() = 0;

signals:

public slots:
};

dasRicardo

Hmm can u show me the constructor implementation?

themts

At this moment the constructors are just empty.

TestItem::TestItem()
{
}

dasRicardo

@themts said:

QQmlListProperty<TestItem> TestClass::lstTestItems() const
{
return QQmlListProperty<TestItem>(this, 0, &TestClass::count_lstTestItems, &TestClass::at_lstTestItems);
}

Why this?

In my impelentation it looks diffrent.

<pre><code>
//implementation of the getter
QQmlListProperty<Object> YourClass::fields() {
return QQmlListProperty<Object>(this, this->m_fields);
}
</code></pre>

themts

QQmlListProperty has 3 constructor. I'm using this one:
http://doc.qt.io/qt-5/qqmllistproperty.html#QQmlListProperty-4

That way I can use it as a "virtual" list.
Anyway, even if I use it your way - which is not recommended - it shows the same error.
"Generally this constructor should not be used in production code, as a writable QList violates QML's memory management rules. However, this constructor can be very useful while prototyping."

QList<TestItem*> m_lstTestItems;

return QQmlListProperty<TestItem>(this, this->m_lstTestItems);

dasRicardo

OK, thanks for your hints. I will definitely change this. I saw this in different sample codes. But my c++ and QT knowledge is very nooby :) Sorry that i can't help u. Not really an idea.

dasRicardo

Can u show me the constructor implementation of your NChartRenderItem class?

themts

I really don't understand why it's not working.
I even tried to use Q_PROPERTY(QQmlListProperty<QObject> ... -> same result

I don't get it. The error-message (C2665) seems to be wrong as well: it says 5 overloads.
Actually there are only 4.

Does anyone has an idea?
Btw. I want to use QQmlListProperty as a datamodel for a listview.

swegmann

Can you show us the full error message of the compiler for the case where you give it the count and at functions? I think there might be some helpfull information about this issue.

themts

solved :-)
no one saw it ;-)

public:
    QQmlListProperty<TestItem> lstTestItems() const;

this can't be const. Thats it.