QML视图在向QAbstractListModel模型添加新项时不会更新

  • Z时代
  • 2024-01-10
  • 分类：问答

我已经想出如何将从QAbstractListModel派生的模型绑定到QML视图。QML视图在向QAbstractListModel模型添加新项时不会更新

但是，我累了的下一件事是行不通的。如果新模型添加到模型中，QML视图将不会更新。这是为什么？

DataObject.h

class DataObject { 
    public: 
     DataObject(const QString &firstName, 
        const QString &lastName): 
      first(firstName), 
      last(lastName) {} 
     QString first; 
     QString last; 
};

SimpleListModel.h

class SimpleListModel : public QAbstractListModel 
{ 
    Q_OBJECT 
    enum /*class*/ Roles { 
     FIRST_NAME = Qt::UserRole, 
     LAST_NAME 
    }; 
    public: 
     SimpleListModel(QObject *parent=0); 
     QVariant data(const QModelIndex &index, int role) const; 
     Q_INVOKABLE int rowCount(const QModelIndex &parent = QModelIndex()) const; 
     QHash<int, QByteArray> roleNames() const; 
     void addName(QString firstName, QString lastName); 
    private: 
     Q_DISABLE_COPY(SimpleListModel); 
     QList<DataObject*> m_items; 
};

SimpleListModel.cpp

SimpleListModel::SimpleListModel(QObject *parent) : 
    QAbstractListModel(parent) 
{ 
    DataObject *first = new DataObject(QString("Firstname01"), QString("Lastname01")); 
    DataObject *second = new DataObject(QString("Firstname02"), QString("Lastname02")); 
    DataObject *third = new DataObject(QString("Firstname03"), QString("Lastname03")); 
    m_items.append(first); 
    m_items.append(second); 
    m_items.append(third); 
} 
QHash<int, QByteArray> SimpleListModel::roleNames() const 
{ 
    QHash<int, QByteArray> roles; 
    roles[/*Roles::*/FIRST_NAME] = "firstName"; 
    roles[/*Roles::*/LAST_NAME] = "lastName"; 
    return roles; 
} 
void SimpleListModel::addName(QString firstName, QString lastName) 
{ 
    DataObject *dataObject = new DataObject(firstName, lastName); 
    m_items.append(dataObject); 
    emit dataChanged(this->index(m_items.size()), this->index(m_items.size())); 
} 
int SimpleListModel::rowCount(const QModelIndex &) const 
{ 
    return m_items.size(); 
} 
QVariant SimpleListModel::data(const QModelIndex &index, int role) const 
{ 
    //--- Return Null variant if index is invalid 
    if(!index.isValid()) 
     return QVariant(); 
    //--- Check bounds 
    if(index.row() > (m_items.size() - 1)) 
     return QVariant(); 
    DataObject *dobj = m_items.at(index.row()); 
    switch (role) 
    { 
     case /*Roles::*/FIRST_NAME: 
      return QVariant::fromValue(dobj->first); 
     case /*Roles::*/LAST_NAME: 
      return QVariant::fromValue(dobj->last); 
     default: 
      return QVariant(); 
    } 
}

AppCore.h

class AppCore : public QObject 
{ 
    Q_OBJECT 
    Q_PROPERTY(SimpleListModel *simpleListModel READ simpleListModel CONSTANT) 
    public: 
     explicit AppCore(QObject *parent = 0); 
     SimpleListModel *simpleListModel() const; 
    public slots: 
     void addName(); 
    private: 
     SimpleListModel *m_SimpleListModel; 
};

AppCore.cpp

AppCore::AppCore(QObject *parent) : 
    QObject(parent) 
{ 
    m_SimpleListModel = new SimpleListModel(this); 
} 
SimpleListModel *AppCore::simpleListModel() const 
{ 
    return m_SimpleListModel; 
} 
void AppCore::addName() 
{ 
    m_SimpleListModel->addName("FirstnameNEW", "LastnameNEW"); 
}

的main.cpp

int main(int argc, char *argv[]) 
{ 
    QGuiApplication a(argc, argv); 
    QQuickView *view = new QQuickView(); 
    AppCore *appCore = new AppCore(); 
    qRegisterMetaType<SimpleListModel *>("SimpleListModel"); 
    view->engine()->rootContext()->setContextProperty("appCore", appCore); 
    view->setSource(QUrl::fromLocalFile("main.qml")); 
    view->show(); 
    return a.exec(); 
}

main.qml

// ... 
ListView { 
    id: myListView 
    anchors.fill: parent 
    delegate: myDelegate 
    model: appCore.simpleListModel 
} 
MouseArea { 
    anchors.fill: parent 
    onClicked: { 
     appCore.addName() 
     console.log('rowCount: ' + appCore.simpleListModel.rowCount()) 
    } 
} 
//...

回答：

你应该调用beginInsertRows和endInsertRows代替发射信号

void SimpleListModel::addName(QString firstName, QString lastName) 
{ 
    DataObject *dataObject = new DataObject(firstName, lastName); 
    // tell QT what you will be doing 
    beginInsertRows(ModelIndex(),m_items.size(),m_items.size()); 
    // do it 
    m_items.append(dataObject); 
    // tell QT you are done 
    endInsertRows(); 
}

的这两个功能上发射所需的所有信号

回答：

你忽略了一个QAbstractItemModel的语义。有两种类型的信号，一个模型必须发出：

  • 数据变化的信号：它们必须发出后的数据被改变。数据变化是现有项目价值的变化。对模型的其他更改是而不是称为数据更改 - 这里的术语具有特定含义。

  • 结构变化的信号：它们必须和之前任何结构变化后射出。结构变化是添加或删除任何项目。帮助功能beginXxxYyy和endXxxYyy发出这些信号。

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