Qgis属性显示
1、部分有关类介绍
————————————-class：QgsDualView—————————————-
/初始化属性对话框
void QgsDualView::init( QgsVectorLayer* layer, QgsMapCanvas* mapCanvas, const QgsFeatureRequest &request,
const QgsAttributeEditorContext &context )
//初始化图层的属性缓存对象
void QgsDualView::initLayerCache( QgsVectorLayer* layer, bool cacheGeometry )
{
初始化mLayerCache 对象
}
//初始化属性表
void QgsDualView::initModels( QgsMapCanvas* mapCanvas, const QgsFeatureRequest& request )
{
- 初始化mMasterModel对象，并设置属性表多少列
- 调用mMasterModel对象的函数::loadAttributes() 加载属性字段
- 调用mMasterModel对象的函数::loadLayer() 加载图层数据
}
————————————-class：QgsAttributeTableModel—————————————-
//加载图层数据
void QgsAttributeTableModel::loadLayer()
{
// make sure attributes are properly updated before caching the data
// (emit of progress() signal may enter event loop and thus attribute
// table view may be updated with inconsistent model which may assume
// wrong number of attributes)
loadAttributes(); //加载属性字段
beginResetModel();
if ( rowCount() != 0 )
{
removeRows( 0, rowCount() );
}
// mLayerCache对象获取要素
QgsFeatureIterator features = mLayerCache->getFeatures( mFeatureRequest );
int i = 0;
QTime t;
t.start();
while ( features.nextFeature( mFeat ) )
{
++i;
if ( t.elapsed() > 1000 )
{
bool cancel = false;
emit progress( i, cancel );
if ( cancel )
break;
t.restart();
}
featureAdded( mFeat.id() );
}
emit finished();
connect( mLayerCache, SIGNAL( invalidated() ), this, SLOT( loadLayer() ), Qt::UniqueConnection );
endResetModel();
}————————————-class：QgsVectorLayerCache（缓存要素）—————————————-
//成员函数部分解释
class CORE_EXPORT QgsVectorLayerCache : public QObject
{
Q_OBJECT
private:
/**
* This is a wrapper class around a cached @link QgsFeature @endlink, which will inform the cache, when it has been deleted, so indexes can be updated that the wrapped feature needs to be fetched again if needed.
*/
class QgsCachedFeature
{
public:
/**
* Will create a new cached feature.
* @param feat The feature to cache. A copy will be made.
* @param vlCache The cache to inform when the feature has been removed from the cache.
*/
QgsCachedFeature( const QgsFeature& feat, QgsVectorLayerCache* vlCache )
: mCache( vlCache )
{
mFeature = new QgsFeature( feat );
}
~QgsCachedFeature()
{
// That's the reason we need this wrapper:
// Inform the cache that this feature has been removed
mCache->featureRemoved( mFeature->id() );
delete mFeature;
}
inline const QgsFeature* feature() { return mFeature; }
private:
QgsFeature* mFeature;
QgsVectorLayerCache* mCache;
friend class QgsVectorLayerCache;
Q_DISABLE_COPY( QgsCachedFeature )
};
public:
QgsVectorLayerCache( QgsVectorLayer* layer, int cacheSize, QObject* parent = nullptr );
~QgsVectorLayerCache();
/**
* 设置最大缓存要素的数量
*/
void setCacheSize( int cacheSize );
/**
* @brief
* Returns the maximum number of features this cache will hold.
* In case full caching is enabled, this number can change, as new features get added.
*
* @return int
*/
int cacheSize();
/**
* 启用或禁用缓存的几何图形
* @param cacheGeometry Enable or disable the caching of geometries
*/
void setCacheGeometry( bool cacheGeometry );
/**
* 设置缓存的属性子集
* @param attributes The attributes to be cached
*/
void setCacheSubsetOfAttributes( const QgsAttributeList& attributes );
/**
* 缓存属性的子集将自动扩展到包括新添加的属性
* @param cacheAddedAttributes Automatically cache new attributes
*/
void setCacheAddedAttributes( bool cacheAddedAttributes );
/**
* @brief
* 如果启用,将缓存中的所有功能。缓存大小将逐步增加提供的所有功能空间
* 所有功能被启用时,将读入缓存。这个特性将最有可能被用于缓慢的数据源,请注意,调用这个方法可能需要很长时间。
* @param fullCache True: enable full caching, False: disable full caching
*/
void setFullCache( bool fullCache );
/**
* @brief
* Adds a {@link QgsAbstractCacheIndex} to this cache. Cache indices know about features present in this cache and decide,
* if enough information is present in the cache to respond to a {@link QgsFeatureRequest}.
* The layer cache will take ownership of the index.
* @param cacheIndex The cache index to add.
*/
void addCacheIndex( QgsAbstractCacheIndex *cacheIndex );
/**
* 查询图层缓存的要素
* 如果VectorLayerCache(而且它的任何指数)能够满足要求,返回的{ @link QgsFeatureIterator }将遍历所有缓存要素。
* 如果从缓存的要素不能得到满足要求，部分或者所有的要素将会通过数据调度获得。
* @param featureRequest 请求指定过滤器和必需的数据
* @return 返回满足请求的数据容器
*/
QgsFeatureIterator getFeatures( const QgsFeatureRequest& featureRequest = QgsFeatureRequest() );
/**
* 判断缓存要素容器中包含当前要素
* @param fid The feature id to look for
* @return True if this id is in the cache
*/
bool isFidCached( const QgsFeatureId fid );
/**
* 根据featureId获得要素，要考虑盗更改的添加的删除的和原要素
* @param featureId The id of the feature to query
* @param feature The result of the operation will be written to this feature
* @param skipCache Will query the layer regardless if the feature is in the cache already
* @return true in case of success
*/
bool featureAtId( QgsFeatureId featureId, QgsFeature &feature, bool skipCache = false );
/**
* 从要素缓存容器中删除缓存的要素
* @param fid The id of the feature to delete
* @return true if the feature was removed, false if the feature id was not found in the cache
*/
bool removeCachedFeature( QgsFeatureId fid );
/**
* Returns the layer to which this cache belongs
*/
QgsVectorLayer* layer();
protected:
/**
* @brief
* Gets called, whenever the full list of feature ids for a certain request is known.
* Broadcasts this information to indices, so they can update their tables.
* @param featureRequest The feature request that was answered
* @param fids The feature ids that have been returned
*/
void requestCompleted( const QgsFeatureRequest& featureRequest, const QgsFeatureIds& fids );
/**
* @brief
* Gets called, whenever a feature has been removed.
* Broadcasts this information to indices, so they can invalidate their cache if required.
* @param fid The feature id of the removed feature.
*/
void featureRemoved( QgsFeatureId fid );
/**
* @brief
* Checks if the information required to complete the request is cached.
* i.e. If all attributes required and the geometry is held in the cache.
* Please note, that this does not check, if the requested features are cached.
*
*
* @param featureRequest The {@link QgsFeatureRequest} to be answered
* @return True if the information is being cached, false if not
*/
bool checkInformationCovered( const QgsFeatureRequest& featureRequest );
signals:
/**
* 缓存要素时，这个信号不断通知工程和取消当前操作
* @param i The number of already fetched features
* @param cancel 引用bool型变量，设置true此操作将被取消
*
* @note not available in python bindings
*/
void progress( int i, bool& cancel );
/**
* When filling the cache, this signal gets emitted once the cache is fully initialized.
*/
void finished();
/**
* @brief Is emitted when the cached layer is deleted. Is emitted when the cached layers layerDelete()
* signal is being emitted, but before the local reference to it has been set to NULL. So call to
* @link layer() @endlink will still return a valid pointer for cleanup purpose.
*/
void cachedLayerDeleted();
/**
* @brief Is emitted when an attribute is changed. Is re-emitted after the layer itself emits this signal.
* You should connect to this signal, to be sure, to not get a cached value if querying the cache.
*/
void attributeValueChanged( QgsFeatureId fid, int field, const QVariant &value );
/**
* Is emitted, when a new feature has been added to the layer and this cache.
* You should connect to this signal instead of the layers', if you want to be sure
* that this cache has updated information for the new feature
*
* @param fid The featureid of the changed feature
*/
void featureAdded( QgsFeatureId fid );
/**
* The cache has been invalidated and cleared.
*/
void invalidated();
private slots:
void onAttributeValueChanged( QgsFeatureId fid, int field, const QVariant& value );
void featureDeleted( QgsFeatureId fid );
void onFeatureAdded( QgsFeatureId fid );
void attributeAdded( int field );
void attributeDeleted( int field );
void geometryChanged( QgsFeatureId fid, QgsGeometry& geom );
void layerDeleted();
void invalidate();
private:
inline void cacheFeature( QgsFeature& feat )
{
QgsCachedFeature* cachedFeature = new QgsCachedFeature( feat, this );
mCache.insert( feat.id(), cachedFeature );
}
QgsVectorLayer* mLayer;
QCache< QgsFeatureId, QgsCachedFeature > mCache;
bool mCacheGeometry;
bool mFullCache;
QList mCacheIndices;
QgsAttributeList mCachedAttributes;
}; 2、技术流程图
Created with Raphaël 2.1.0QgsDualView::initQgsDualView::initLayerCacheQgsDualView::initModelsQgsAttributeTableModel::loadLayer()QgsAttributeTableModel::loadAttributes()QgsAttributeTableModel::loadFeatureAtIdQgsVectorLayerCache::featureAtIdQgsVectorLayerCache::getFeaturesQgsVectorLayerCache::checkInformationCovered
3后续补充：
从图层中获取要素，并要素存入mCache存储要素容器，执行顺序
void QgsAttributeTableModel::prefetchSortData( const QString& expressionString )
bool QgsAbstractFeatureIterator::nextFeature( QgsFeature& f )
bool QgsCachedFeatureWriterIterator::fetchFeature( QgsFeature& f )
bool QgsAbstractFeatureIterator::nextFeature( QgsFeature& f )
bool QgsVectorLayerFeatureIterator::fetchFeature( QgsFeature& f )
bool QgsAbstractFeatureIterator::nextFeature( QgsFeature& f )
QgsVectorLayerCache::cacheFeature( QgsFeature& feat )
从mCache存储要素容器获取要素，将要素属性贴到属性表中
//将mFeat对象中的属性字段值存储到属性表中
QgsAttributeTableModel::data()
//获取第fid个要素对象，并将对象存储到mFeat对象中
QgsAttributeTableModel::loadFeatureAtId( QgsFeatureId fid )
//从mCache存储要素容器中获取要素存储到feature
QgsVectorLayerCache::featureAtId( QgsFeatureId featureId, QgsFeature& feature, bool skipCache )
//将mFeat对象中的属性字段值存储到属性表中
QgsAttributeTableModel::data()
//从数据获取要素
QgsCachedFeatureWriterIterator::fetchFeature( QgsFeature& f )