qml中调取数据库中的数据显示在SwitchDelegate控件中

如果你使用的是Qt的Sql模块连接数据库，可以通过以下步骤在QML中调用数据库中的数据并显示在SwitchDelegate控件中：

1. 在C++中创建一个继承自QAbstractListModel的模型类，重写rowCount()、data()等方法，用于从数据库中获取数据并在QML中显示。

class SwitchModel : public QAbstractListModel
{
    Q_OBJECT

public:
    // 构造函数和析构函数
    // ...

    // 重写方法
    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;

private:
    QSqlDatabase m_db;
};

2. 在rowCount()方法中返回数据库中数据的行数。

int SwitchModel::rowCount(const QModelIndex &parent) const
{
    Q_UNUSED(parent)
    QSqlQuery query(m_db);
    query.exec("SELECT COUNT(*) FROM switches");
    if (query.next()) {
        return query.value(0).toInt();
    }
    return 0;
}

3. 在data()方法中返回指定行和列的数据，根据role参数决定返回什么类型的数据。

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

    if (index.row() < 0 || index.row() >= rowCount())
        return QVariant();

    if (role == Qt::DisplayRole || role == Qt::EditRole) {
        QSqlQuery query(m_db);
        query.prepare("SELECT name, status FROM switches LIMIT 1 OFFSET :row");
        query.bindValue(":row", index.row());
        if (query.exec() && query.next()) {
            if (query.columnCount() == 2) {
                if (query.value(1).toBool()) {
                    return QVariant(QStringLiteral("On"));
                } else {
                    return QVariant(QStringLiteral("Off"));
                }
            }
        }
    }

    return QVariant();
}

4. 在QML文件中使用ListView控件显示数据，并设置SwitchDelegate控件用于显示开关状态。

ListView {
    width: 200
    height: 200
    model: switchModel
    delegate: SwitchDelegate {
        text: model.name
        checked: model.status === "On"
    }
}

注意：需要在C++中将SwitchModel类注册为一个可在QML中使用的类型，可以使用qmlRegisterType()函数实现。

完整的代码可以参考以下示例：

#include <QAbstractListModel>
#include <QSqlDatabase>
#include <QSqlQuery>
#include <QSqlError>
#include <QDebug>

class SwitchModel : public QAbstractListModel
{
    Q_OBJECT

public:
    explicit SwitchModel(QObject *parent = nullptr)
        : QAbstractListModel(parent)
        , m_db(QSqlDatabase::addDatabase("QSQLITE"))
    {
        m_db.setDatabaseName("switches.db");
        if (!m_db.open()) {
            qWarning() << "Failed to open database:" << m_db.lastError().text();
        }
    }

    int rowCount(const QModelIndex &parent = QModelIndex()) const override
    {
        Q_UNUSED(parent)
        QSqlQuery query(m_db);
        query.exec("SELECT COUNT(*) FROM switches");
        if (query.next()) {
            return query.value(0).toInt();
        }
        return 0;
    }

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override
    {
        if (!index.isValid())
            return QVariant();

        if (index.row() < 0 || index.row() >= rowCount())
            return QVariant();

        if (role == Qt::DisplayRole || role == Qt::EditRole) {
            QSqlQuery query(m_db);
            query.prepare("SELECT name, status FROM switches LIMIT 1 OFFSET :row");
            query.bindValue(":row", index.row());
            if (query.exec() && query.next()) {
                if (query.columnCount() == 2) {
                    if (query.value(1).toBool()) {
                        return QVariant(QStringLiteral("On"));
                    } else {
                        return QVariant(QStringLiteral("Off"));
                    }
                }
            }
        }

        return QVariant();
    }

private:
    QSqlDatabase m_db;
};

#include <QApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    SwitchModel switchModel;

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

    return app.exec();
}

#include <QAbstractButton>
#include <QCheckBox>
#include <QPainter>
#include <QStyleOption>

class SwitchDelegate : public QAbstractButton
{
    Q_OBJECT

public:
    explicit SwitchDelegate(QWidget *parent = nullptr)
        : QAbstractButton(parent)
        , m_checked(false)
    {}

    QSize sizeHint() const override
    {
        return QSize(60, 30);
    }

    bool isChecked() const override
    {
        return m_checked;
    }

    void setChecked(bool checked) override
    {
        if (m_checked != checked) {
            m_checked = checked;
            emit toggled(m_checked);
            update();
        }
    }

protected:
    void paintEvent(QPaintEvent *event) override
    {
        Q_UNUSED(event)
        QPainter painter(this);
        painter.setRenderHint(QPainter::Antialiasing);

        QBrush bgBrush(m_checked ? QColor("#4CD964") : QColor("#B2B2B2"));
        painter.setBrush(bgBrush);
        painter.setPen(Qt::NoPen);
        painter.drawRoundedRect(rect(), 15, 15);

        QBrush fgBrush(m_checked ? QColor("#FFFFFF") : QColor("#FFFFFF"));
        painter.setBrush(fgBrush);
        QRectF fgRect = QRectF(0, 0, width()/2, height());
        if (m_checked) {
            fgRect.translate(width()/2, 0);
        }
        painter.drawEllipse(fgRect);
    }

    void mousePressEvent(QMouseEvent *event) override
    {
        if (event->button() == Qt::LeftButton) {
            setChecked(!m_checked);
        }
    }

private:
    bool m_checked;
};

#include <QQmlComponent>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    SwitchModel switchModel;

    QQmlEngine engine;
    QQmlComponent component(&engine);
    component.setData(R"qml(
        import QtQuick 2.15
        import QtQuick.Controls 2.15

        ListView {
            width: 200
            height: 200
            model: switchModel
            delegate: SwitchDelegate {
                text: model.name
                checked: model.status === "On"
            }
        }
    )qml", QUrl());
    QObject *rootObject = component.create();

    return app.exec();
}

#include <QQmlEngine>
#include <QQmlContext>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    SwitchModel switchModel;

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

    return app.exec();
}