Using C++ Models in QML

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内容图文

参考youtube上qt官方的视频：https://www.youtube.com/watch?v=9BcAYDlpuT8
youtube视频下方本来有github地址的，进去后代码为空，就照着视频教程把代码重新敲了一遍。
主要功能
1.实现了一个简单的待办事项
2.删除勾选的一行记录，也可以删除多行已经勾选的记录
是用C++继承QAbstractListModel实现了model，然后给qml调用。
运行效果：

源码之前了无秘密：
ToDoList.qml

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3

import ToDo 1.0
ColumnLayout
{
    Frame {
        ListView {
            implicitWidth: 250
            implicitHeight: 250
            clip: true

            /*
            model: ListModel {
                ListElement {
                    done: true
                    description: "Wash the car"
                }
                ListElement {
                    done: true
                    description: "fix the sink"
                }
            }
            */
            model: ToDoModel {
                list:  toDoList
            }

            delegate: RowLayout {
                width: parent.width
                CheckBox {
                    checked: model.done
                    onClicked: model.done = checked
                }
                TextField {
                    text: model.description
                    onEditingFinished: model.description = text
                    Layout.fillWidth:  true
                }
            }
        }
    }

    RowLayout {
        Button {
            text: qsTr("Add new item")
            onClicked: toDoList.appendItem()
            Layout.fillWidth: true
        }
        Button {
            text: qsTr("Remove completed")
            onClicked: toDoList.removeCompleteItems()
            Layout.fillWidth: true
        }
    }
}

main.qml文件：

import QtQuick 2.9
import QtQuick.Window 2.2

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

    ToDoList {
        anchors.centerIn: parent
    }
}

todolist.h文件：

#ifndef TODOLIST_H
#define TODOLIST_H

#include <QObject>
#include <QVector>

struct ToDoItem
{
    bool done;
    QString description;
};

class ToDoList : public QObject
{
    Q_OBJECT
public:
    explicit ToDoList(QObject *parent = nullptr);

    QVector<ToDoItem> items() const;

    bool setItemAt(int index, const ToDoItem &item);


signals:
    void preItemAppended();
    void postItemAppended();

    void preItemRemoved(int index);
    void postItemRemoved();

public slots:
    void appendItem();
    void removeCompleteItems();

private:
    QVector<ToDoItem> mItems;
};

#endif // TODOLIST_H

todolist.cpp文件：

#include "todolist.h"

ToDoList::ToDoList(QObject *parent) : QObject(parent)
{
    mItems.append({true, QStringLiteral("Wash the car")});
    mItems.append({true, QStringLiteral("Fix the car")});
}

QVector<ToDoItem> ToDoList::items() const
{
    return mItems;
}

bool ToDoList::setItemAt(int index, const ToDoItem &item)
{
    if (index < 0 || index >= mItems.size())
        return false;

    const ToDoItem &oldItem = mItems.at(index);
    if (item.done == oldItem.done && item.description == oldItem.description)
        return false;

    mItems[index] = item;
    return true;
}

void ToDoList::appendItem()
{
    emit preItemAppended();

    ToDoItem item;
    item.done = false;
    mItems.append(item);

    emit postItemAppended();
}

void ToDoList::removeCompleteItems()
{
    for (int i = 0; i < mItems.size(); ) {
        if (mItems.at(i).done) {
            emit preItemRemoved(i);

            mItems.removeAt(i);

            emit postItemRemoved();
        } else {
            ++i;
        }
    }
}

todomodel.h文件：

#ifndef TODOMODEL_H
#define TODOMODEL_H

#include <QAbstractListModel>

class ToDoList;

class ToDoModel : public QAbstractListModel
{
    Q_OBJECT
    Q_PROPERTY(ToDoList *list READ list WRITE setList)

public:
    explicit ToDoModel(QObject *parent = nullptr);

    enum {
        DoneRole = Qt::UserRole,
        DescriptionRole
    };

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

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;

    // Editable:
    bool setData(const QModelIndex &index, const QVariant &value,
                 int role = Qt::EditRole) override;

    Qt::ItemFlags flags(const QModelIndex& index) const override;

    virtual QHash<int, QByteArray> roleNames() const override;


    ToDoList *list() const;
    void setList(ToDoList *list);

private:
    ToDoList *mList;
};

#endif // TODOMODEL_H

todomodel.cpp文件：

#include "todomodel.h"
#include "todolist.h"

ToDoModel::ToDoModel(QObject *parent)
    : QAbstractListModel(parent)
    , mList(nullptr)
{
}

int ToDoModel::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() || !mList)
        return 0;

    // FIXME: Implement me!
    return mList->items().size();
}

QVariant ToDoModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid() || !mList)
        return QVariant();

    // FIXME: Implement me!
    const ToDoItem item = mList->items().at(index.row());
    switch (role) {
    case DoneRole:
        return QVariant(item.done);
    case DescriptionRole:
        return QVariant(item.description);
    }
    return QVariant();
}

bool ToDoModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    if (!mList)
        return false;

    ToDoItem item = mList->items().at(index.row());
    switch (role) {
    case DoneRole:
        item.done = value.toBool();
        break;
    case DescriptionRole:
        item.description = value.toString();
        break;
    }

    if (mList->setItemAt(index.row(), item)) {
        // FIXME: Implement me!
        emit dataChanged(index, index, QVector<int>() << role);
        return true;
    }
    return false;
}

Qt::ItemFlags ToDoModel::flags(const QModelIndex &index) const
{
    if (!index.isValid())
        return Qt::NoItemFlags;

    return Qt::ItemIsEditable; // FIXME: Implement me!
}

QHash<int, QByteArray> ToDoModel::roleNames() const
{
    QHash<int, QByteArray> names;
    names[DoneRole] = "done";
    names[DescriptionRole] = "description";
    return names;
}

ToDoList *ToDoModel::list() const
{
    return mList;
}

void ToDoModel::setList(ToDoList *list)
{
    beginResetModel();

    if (mList)
        mList->disconnect(this);

    mList = list;

    if (mList) {
        connect(mList, &ToDoList::preItemAppended, this, [=](){
            const int index = mList->items().size();
            beginInsertRows(QModelIndex(), index, index);
        });
        connect(mList, &ToDoList::postItemAppended, this, [=](){
            endInsertRows();
        });

        connect(mList, &ToDoList::preItemRemoved, this, [=](int index){
            beginRemoveRows(QModelIndex(), index, index);
        });
        connect(mList, &ToDoList::postItemRemoved, this, [=](){
            endRemoveRows();
        });
    }

    endResetModel();
}

main.cpp文件：

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

#include "todomodel.h"
#include "todolist.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    qmlRegisterType<ToDoModel>("ToDo", 1, 0, "ToDoModel");
    qmlRegisterUncreatableType<ToDoList>("ToDo", 1, 0, "toDoList", QStringLiteral("ToDoLsit should not be created in QML"));
    ToDoList toDoList;

    QQmlApplicationEngine engine;
    engine.rootContext()->setContextProperty(QStringLiteral("toDoList"), &toDoList);
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));


    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

其中class ToDoModel : public QAbstractListModel
利用qt creator进行添加比较方便：


视频中是勾选的第三个，其余的可以根据需要勾选。

利用代码补齐，选中mList后，用Alt+Enter可以自动添以下两个函数：
ToDoList *list() const;
void setList(ToDoList *list);
然后发现其他人也看过这个视频，参考：
https://blog.csdn.net/qq_32768743/article/details/80863753
官方文档：https://doc.qt.io/qt-5/qtquick-modelviewsdata-cppmodels.html

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