今天关于Q_m_l 的研究

Q——ML的开发流程（结合C++）：

新建一个C++类，通过 Q_PROPERTY宏设置Q_ML_对象属性，(QString name READ name WRITE setName)

Q_PROPERTY(QColor color READ color WRITE setColor)，

其中 qmlRegisterType<PieChart>("Charts", 1, 0, "PieChart"); 用于注册Qml对象，版本为1.0

A common task when extending QML is to provide a new QML type that supports some custom functionality beyond what is provided by the built-in Qt Quick types. For example, this could be done to implement particular data models, or provide types with custom
painting and drawing capabilities, or access system features like network programming that are not accessible through built-in QML features.

In this tutorial, we will show how to use the C++ classes in the Qt Quick module to extend QML. The end result will be a simple Pie Chart display implemented by several custom QML types connected together through QML features like bindings and signals, and
made available to the QML runtime through a plugin.

To begin with, let's create a new QML type called "PieChart" that has two properties: a name and a color. We will make it available in an importable type namespace called "Charts", with a version of 1.0.

We want this PieChart type to be usable from QML like this:

import Charts 1.0

PieChart {

width: 100; height: 100

name: "A simple pie chart"

color: "red"

}

To do this, we need a C++ class that encapsulates this PieChart type and its two properties. Since QML makes extensive use of Qt's meta object system, this new class must:

Inherit from QObject

Declare its properties using the Q_PROPERTY macro

Here is our PieChart class, defined in piechart.h:

#include <QtQuick/QQuickPaintedItem>

#include <QColor>

class PieChart : public QQuickPaintedItem

{

Q_OBJECT

Q_PROPERTY(QString name READ name WRITE setName)

Q_PROPERTY(QColor color READ color WRITE setColor)

public:

PieChart(QQuickItem *parent = 0);

QString name() const;

void setName(const QString &name);

QColor color() const;

void setColor(const QColor &color);

void paint(QPainter *painter);

private:

QString m_name;

QColor m_color;

};

The class inherits from QQuickPaintedItem because we want to override QQuickPaintedItem::paint() in perform drawing operations with the QPainter API. If the class just represented some data type and was not an item that actually needed to be displayed, it could
simply inherit from QObject. Or, if we want to extend the functionality of an existing QObject-based class, it could inherit from that class instead. Alternatively, if we want to create a visual item that doesn't need to perform drawing operations with the
QPainter API, we can just subclass QQuickItem.

The PieChart class defines the two properties, name and color, with the Q_PROPERTY macro, and overrides QQuickPaintedItem::paint(). The class implementation in piechart.cpp simply sets and returns the m_name and m_color values as appropriate, and implements
paint() to draw a simple pie chart. It also turns off the QGraphicsItem::ItemHasNoContents flag to enable painting:

PieChart::PieChart(QQuickItem *parent)

: QQuickPaintedItem(parent)

{

}

...

void PieChart::paint(QPainter *painter)

{

QPen pen(m_color, 2);

painter->setPen(pen);

painter->setRenderHints(QPainter::Antialiasing, true);

painter->drawPie(boundingRect().adjusted(1, 1, -1, -1), 90 * 16, 290 * 16);

}

Now that we have defined the PieChart type, we will use it from QML. The app.qml file creates a PieChart item and display the pie chart's details using a standard QML Text item:

import Charts 1.0

import QtQuick 2.0

Item {

width: 300; height: 200

PieChart {

id: aPieChart

anchors.centerIn: parent

width: 100; height: 100

name: "A simple pie chart"

color: "red"

}

Text {

anchors { bottom: parent.bottom; horizontalCenter: parent.horizontalCenter; bottomMargin: 20 }

text: aPieChart.name

}

}

Notice that although the color is specified as a string in QML, it is automatically converted to a QColor object for the PieChart color property. Automatic conversions are provided for various other basic types; for example, a string like "640x480" can be automatically
converted to a QSize value.

We'll also create a C++ application that uses a QQuickView to run and display app.qml. The application must register the PieChart type using the qmlRegisterType() function, to allow it to be used from QML. If you don't register the type, app.qml won't be able
to create a PieChart.

Here is the application main.cpp:

#include "piechart.h"

#include <QtQuick/QQuickView>

#include <QGuiApplication>

int main(int argc, char *argv[])

{

QGuiApplication app(argc, argv);

qmlRegisterType<PieChart>("Charts", 1, 0, "PieChart");

QQuickView view;

view.setResizeMode(QQuickView::SizeRootObjectToView);

view.setSource(QUrl::fromLocalFile("app.qml"));

view.show();

return app.exec();

}

This call to qmlRegisterType() registers the PieChart type as a type called "PieChart", in a type namespace called "Charts", with a version of 1.0.

Lastly, we write a .pro project file that includes the files and the declarative library: