[C++知识库]QT C++ model 的使用实例

描述：在QML中，当需要少量数据时，QML中直接用原生模型是非常方便。

当数据较为复杂或者想在c++里操纵数据时，可以在C++中自定义自己的Model并在qml中展示数据，这样会更加稳定可靠而且避免卡顿现象。

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "MyListModel.h"
#include <QQmlContext>


int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
//    engine.rootContext()->setContextProperty("MyListModel",MyListModel::getInstance());//方法1 注册自定义model
    qmlRegisterSingletonInstance("MyModel",1,0,"MyListModel",MyListModel::getInstance());//方法2
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

MyListModel.(h/cpp)

#ifndef MYLISTMODEL_H
#define MYLISTMODEL_H

#include <QAbstractListModel>

class MyData {
public:
    MyData(QString s,int a):m_name(s),m_age(a){

    };
    QString m_name;
    int m_age;
};

class MyListModel : public QAbstractListModel
{
    Q_OBJECT

    enum myRole {
        Name = Qt::DisplayRole+1,
        Age
    };

public:
    explicit MyListModel(QObject *parent = nullptr);
    MyListModel(QString s,int age);
    static MyListModel *getInstance();

    // Basic functionality:
    int rowCount(const QModelIndex &parent = QModelIndex()) const override;

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
    QHash<int, QByteArray> roleNames() const override;
private:

    QList<MyData> m_data;
    static MyListModel *instance;
};

#endif // MYLISTMODEL_H

#include "MyListModel.h"

MyListModel *MyListModel::instance = 0;

MyListModel::MyListModel(QObject *parent)
    : QAbstractListModel(parent)
{
    m_data.append(MyData("tom",12));
    m_data.append(MyData("jack",23));
    m_data.append(MyData("peter",43));
}

MyListModel *MyListModel::getInstance()
{
    if(instance == nullptr){
        instance = new MyListModel();
    }
    return instance;
}


int MyListModel::rowCount(const QModelIndex &parent) const
{
    // For list models only the root node (an invalid parent) should return the list's size. For all
    // other (valid) parents, rowCount() should return 0 so that it does not become a tree model.
    if (parent.isValid())
        return 0;

    // FIXME: Implement me!
    return m_data.count();//返回数据一共有多少行，在listmodel里面一般列是1，所以这里只需要计算rowd的大小
}

QVariant MyListModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid())
        return QVariant();
    if(myRole::Name == role){//根据对应的角色返回对应的值
        return m_data[index.row()].m_name;
    }else if(myRole::Age == role){
        return m_data[index.row()].m_age;
    }
    return QVariant();
}
QHash<int, QByteArray> MyListModel::roleNames() const
{
    QHash<int, QByteArray> roles;
    roles.insert(myRole::Name,"name");//qml yu C++进行映射
    roles.insert(myRole::Age,"age");//qml 使用字符串"age"就可以显示

    return roles;
}

QML:

import QtQuick 2.12
import QtQuick.Window 2.12
import MyModel 1.0

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    ListView {
        anchors.fill: parent
//        model: ListModel {
//            ListElement {
//                name: "zhangsan"
//                age: 12
//            }
//            ListElement {
//                name: "tom"
//                age: 33
//            }
//            ListElement {
//                name: "jack"
//                age: 23
//            }
//        }
        model:MyListModel

        delegate: Text {
            id: txt
            text: name + " " + age;
        }
    }
}

run:

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