Qt信号转发;继承了QAbstractProxyModel

你是对的，文档对此毫无帮助。查看QAbstractProxyModel的源代码，并将其与Qt 5.12中的QSortFilterProxyModel进行比较，可以得出QAbstract ProxyModel绝不处理dataChanged信号的转发！你必须自己做！最好选择一个更复杂的模型，如QSortFilterProxyModel或QIdentityProxy model，它可以为您进行转发。但如果你真的无法绕过它，那么它可能看起来像这样：

/**
 * Proxy model which only returns one data row of the underlying QAbstractItemModel
 * except for the first column. Can be used to separate a model for QTreeView into
 * the tree column and the data columns. This proxy returns the data columns.
 * Can't use QSortFilterProxyModel because it does not allow for only showing one
 * row if its parent is filtered out.
 */
class SingleRowProxy :
    public QAbstractProxyModel
{
    Q_OBJECT;
    using BaseType = QAbstractProxyModel;
    static constexpr auto FIRST_DATA_COLUMN = 1;
public:
    SingleRowProxy( QAbstractItemModel* sourceModel,
                    int                 row,
                    const QModelIndex&  parentIndex,
                    QObject*            parentObject = nullptr ) :
        BaseType( parentObject ),
        m_sourceRow( row ),
        m_sourceParent( parentIndex )
    {
        Q_ASSERT( sourceModel != nullptr );
        setSourceModel( sourceModel );
    }
    void setSourceModel( QAbstractItemModel *newSourceModel ) override
    {
        if ( newSourceModel == sourceModel() ) {
            return;
        }
        beginResetModel();
        disconnect( newSourceModel, nullptr, this, nullptr );
        BaseType::setSourceModel( newSourceModel );
        connect( newSourceModel, &QAbstractItemModel::dataChanged,
                 this, &SingleRowProxy::sourceDataChanged );
        connect( newSourceModel, &QAbstractItemModel::modelAboutToBeReset,
                 this, [this] () { beginResetModel(); } );
        connect( newSourceModel, &QAbstractItemModel::modelReset,
                 this, [this] () { endResetModel(); } );
    }
    QModelIndex
    mapFromSource( const QModelIndex& sourceIndex ) const override
    {
        if ( !sourceIndex.isValid() || ( sourceIndex.column() < FIRST_DATA_COLUMN ) ) {
            return {};
        }
        return index( 0, sourceIndex.column() - FIRST_DATA_COLUMN, QModelIndex() );
    }
    QModelIndex
    mapToSource( const QModelIndex& proxyIndex ) const override
    {
        if ( !proxyIndex.isValid() ) {
            return {};
        }
        return sourceModel()->index( m_sourceRow, 
                                     proxyIndex.column() + FIRST_DATA_COLUMN, 
                                     m_sourceParent );
    }
    QVariant
    data( const QModelIndex& index,
          int                role ) const override
    {
        return sourceModel()->data( mapToSource( index ), role );
    }
    int
    rowCount( [[maybe_unused]] const QModelIndex& parent = QModelIndex() ) const override
    {
        return sourceModel()->hasIndex( m_sourceRow, FIRST_DATA_COLUMN, m_sourceParent ) ? 1 : 0;
    }
    int
    columnCount( [[maybe_unused]] const QModelIndex& parent = QModelIndex() ) const override
    {
        return sourceModel()->columnCount( sourceModel()->index( m_sourceRow, 0, m_sourceParent ) );
    }
    QModelIndex
    index( int                row,
           int                column,
           const QModelIndex& parent ) const override
    {
        if ( !hasIndex( row, column, parent ) ) {
            return {};
        }
        return createIndex( row, column );
    }
    QModelIndex
    parent( [[maybe_unused]] const QModelIndex& child ) const override
    {
        return {};
    }
private slots:
    /**
     * QSortFilterProxyModel does it for us but QAbstractProxyModel does not!
     * So we have to map the source indices and reemit the dataChanged signal. */
    void
    sourceDataChanged( const QModelIndex &topLeft, const QModelIndex &bottomRight, const QVector<int> &roles )
    {
        if ( !topLeft.isValid() || 
             !bottomRight.isValid() || 
             ( topLeft.parent() != bottomRight.parent() ) ) 
        {
            return;
        }
        const auto& parent = topLeft.parent();
        int minRow = std::numeric_limits<int>::max();
        int maxRow = std::numeric_limits<int>::lowest();
        int minCol = std::numeric_limits<int>::max();
        int maxCol = std::numeric_limits<int>::lowest();
        bool foundValidIndex = false;
        for ( int sourceRow = topLeft.row(); sourceRow <= bottomRight.row(); ++sourceRow ) {
            for ( int sourceColumn = topLeft.column(); sourceColumn <= bottomRight.column(); ++sourceColumn ) {
                const auto index = mapFromSource( sourceModel()->index( sourceRow, sourceColumn, topLeft.parent() ) );
                if ( !index.isValid() ) {
                    continue;
                }
                minRow = std::min( minRow, index.row() );
                maxRow = std::max( maxRow, index.row() );
                minCol = std::min( minCol, index.column() );
                maxCol = std::max( maxCol, index.column() );
                foundValidIndex = true;
            }
        }
        if ( foundValidIndex ) {
            emit dataChanged( index( minRow, minCol, parent ), 
                              index( maxRow, maxCol, parent ), 
                              roles );
        }
    }
private:
    const int m_sourceRow;
    const QModelIndex m_sourceParent;
};

您必须进行索引映射，因为代理索引与源模型索引不同！

请注意，这个示例只是非常初级的，可能不适用于任意映射。

请注意，对于一个完整的代理模型，您必须映射并转发所有信号。QSortFilterProxyModel在setSourceModel:中重新连接这些信号

• 数据已更改
• headerData Changed
• 插入的行前后
• 插入的行
• 插入的列
• 列已插入
• 即将删除的行
• 行已删除
• 列即将删除
• 列删除
• 即将移动的行
• 行移动
• 列AboutToBeMoved
• 列移动
• 布局AboutToBeChanged
• 布局已更改
• 型号AboutToBeReset
• modelReset

来自文档：

要子类化QAbstractProxyModel，需要实现mapFromSource（）和mapToSource（）。只有在需要不同于默认行为的行为时，才需要重新实现mapSelectionFromSource（）和mapSelectionToSource（）函数。

没有关于信号的词语。在上述方法的文档中也是如此。这意味着你不需要关心信号，它们会自动发出。

如果class A : public QAbstractProxyModel、class B : public QAbstractItemModel，则某些信号转发和更新良好（dataChanged等）。但有些（如rowsInserted）必须手动连接。

我使用这样的代码：

...
#define COL_ID 0
void A::setSourceModel(QAbstractItemModel *newSourceModel) {
    beginResetModel();
    if (this->sourceModel()) { // disconnect sourceModel signals
        ...
    }
    ...
    QAbstractProxyModel::setSourceModel(newSourceModel);
    if (this->sourceModel()) { // connect sourceModel signals
        ...
        connect(this->sourceModel(), SIGNAL(rowsInserted(QModelIndex,int,int)),
             this, SLOT(sourceRowsInserted(QModelIndex, int, int)));
        ...
    }
    return;
}
...
void A::sourceRowsInserted(const QModelIndex &parent, int first, int last) {
    QModelIndex parentIndex = this->mapFromSource(parent);
    QModelIndex sourceTopIndex = this->sourceModel()->index(first, COL_ID, parent);
    QModelIndex sourceBottomIndex = this->sourceModel()->index(last, COL_ID, parent);
    QModelIndex topIndex = this->mapFromSource(sourceTopIndex);
    QModelIndex bottomIndex = this->mapFromSource(sourceBottomIndex);
    beginInsertRows(parentIndex, topIndex.row(), bottomIndex.row());
    endInsertRows();
    return;
}

如果类类似于class A : public QAbstractProxyModel和class B : public QAbstractItemModel，那么信号和插槽也应该被继承。（除非你想要它的特殊行为。

如果"QAbstractClasses"是A和B的简单成员，则必须"转发"它们