c++ - Qt信号转发；继承QAbstractProxyModel

Question

文档似乎是关于这个的，我在 StackOverflow 和其他地方看到了一堆模棱两可的示例代码，所以......

如果我有一个类 A 实现了一个 QAbstractProxyModel 和一个类 B 实现了一个 QAbstractItemModel 并且我在 A 的实例上调用 setSourceModel(b) 方法，其中 b 是 B 的实例，自动处理转发更新信号，例如 modelReset、rowsInserted 等？还是我必须手动连接所有这些？

Answer 1

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，得出 QAbstractProxyModel 决不会处理 dataChanged 信号的转发!你必须自己做!最好选择更复杂的模型，例如 QSortFilterProxyModel 或 QIdentityProxyModel，它们会为您执行此转发。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;
};

你必须做 index mapping因为代理索引与源模型索引不同!

请注意，此示例只是非常初级的，可能不适用于任意映射。

请注意，对于完整的代理模型，您必须映射和转发所有信号。 QSortFilterProxyModel 在 setSourceModel 中重新连接这些信号:

• 数据已更改
• headerDataChanged
• rowsAboutToBeInserted
• 已插入行
• 关于要插入的列
• 已插入列
• rowsAboutToBeRemoved
• 删除的行数
• 关于删除的列
• 删除的列
• rowsAboutToBeMoved
• 移动的行数
• 列AboutToBeMoved
• columnsMoved
• layoutAboutToBeChanged
• 布局改变
• modelAboutToBeReset
• 模型重置