QML simple extension doesn't work

Question

I'm trying to extend QML with a C++ class. I've started by creating a simple class Line. It calls setters, but doesn't call getters and the paint method. Any ideas why? In QtQuick 1.x I should call setFlag(QGraphicsItem::ItemHasNoContents, false); in the constructor. Probably I should call something similar?

Here is the code:

Line.h

#ifndef LINE_H
#define LINE_H

#include <QQuickPaintedItem>

class Line : public QQuickPaintedItem
{
    Q_OBJECT

    Q_PROPERTY(int x1 READ x1 WRITE setx1 NOTIFY x1Changed)
    Q_PROPERTY(int y1 READ y1 WRITE sety1 NOTIFY y1Changed)
    Q_PROPERTY(int x2 READ x2 WRITE setx2 NOTIFY x2Changed)
    Q_PROPERTY(int y2 READ y2 WRITE sety2 NOTIFY y2Changed)
    Q_PROPERTY(QColor color READ color WRITE setColor NOTIFY colorChanged)
    Q_PROPERTY(int penWidth READ penWidth WRITE setPenWidth NOTIFY penWidthChanged)

public:
    Line(QQuickItem *parent = nullptr);
    ~Line();

    void paint(QPainter *painter) override;

    int x1() const;
    ...

signals:
    void x1Changed(int arg);
    ...

public slots:
    void setx1(int arg);
    ...

private:
    int m_x1;
    ...
};

#endif // LINE_H

Line.cpp

#include "Line.h"

#include <QPen>
#include <QPainter>

Line::Line(QQuickItem *parent) : QQuickPaintedItem(parent)
{

}

Line::~Line()
{

}

void Line::paint(QPainter *painter)
{
    QPen pen(m_color, m_penWidth);
    painter->setPen(pen);
    int x = qMin(m_x1, m_x2) - m_penWidth/2;
    int y = qMin(m_y1, m_y2) - m_penWidth/2;
    painter->drawLine(m_x1 - x, m_y1 - y, m_x2 - x, m_y2 - y);
}

int Line::x1() const
{
    return m_x1;
}
...

void Line::setx1(int arg)
{
    if (m_x1 == arg)
        return;

    m_x1 = arg;
    emit x1Changed(arg);
}
...

Also it is obvious that I've added registration of my class in main: qmlRegisterType("extentiongui", 1, 0, "Line");

My QML code:

    Line {
        id: lineDelimiter
        x1: 863
        x2: 863
        y1: 660
        y2: 800
        penWidth: 8000
        color: "#c2c2c2"
    }

Meefte Meefte · Accepted Answer · 2015-02-04T08:25:25

If your item has visual content, you should set QQuickItem::ItemHasContents flag.

setFlag(QQuickItem::ItemHasContents, true);

Also, you should call update() in setters functions to redraw your item.

void Line::setx1(int arg)
{
    if (m_x1 == arg)
        return;

    m_x1 = arg;
    emit x1Changed(arg);
    update();
}

QML simple extension doesn't work

1 Answers