1.调用

1) QgsMapLayerFactory::createLayer

在QgsMapLayerFactory::createLayer()内判断需创建的图层类型后创建对应的图层对象实例

QgsMapLayerFactory::createLayer(...)
└─new QgsVectorLayer(...)

2) QgsVectorLayer构造函数

当传入的图层路径和providerKey都不为空时，调用父类QgsMapLayer::setDataSource设置数据源

QgsMapLayerFactory::createLayer(...)
└─new QgsVectorLayer(...)
    └─QgsMapLayer::setDataSource(...)

3) QgsMapLayer::setDataSource()

QgsMapLayer::setDataSource内部调用了setDataSourcePrivate()，由于setDataSourcePrivate是虚函数且子类QgsVectorLayer对其进行了实现，所有此时的函数实现为QgsVectorLayer::setDataSourcePrivate()

QgsMapLayerFactory::createLayer(...)
└─new QgsVectorLayer(...)
    └─QgsMapLayer::setDataSource(...)
        └─QgsVectorLayer::setDataSourcePrivate(...)

4) QgsVectorLayer::setDataSourcePrivate

setDataSourcePrivate内调用setDataProvider()设置图层的dataprovider

QgsMapLayerFactory::createLayer(...)
└─new QgsVectorLayer(...)
    └─QgsMapLayer::setDataSource(...)
        └─QgsVectorLayer::setDataSourcePrivate(...)
              └─setDataProvider(...)

2. QgsVectorLayer::setDataProvider()

1) 创建DataProvider对象

通过QgsProviderRegistry::createProvider创建对应的Provider对象

bool QgsVectorLayer::setDataProvider( QString const &provider, const QgsDataProvider::ProviderOptions &options, QgsDataProvider::ReadFlags flags )
{
  ......
  mDataProvider = qobject_cast<QgsVectorDataProvider *>( QgsProviderRegistry::instance()->createProvider( provider, mDataSource, options, flags ) );
  ......
}

2) 如果可以获取图层元数据

bool QgsVectorLayer::setDataProvider( QString const &provider, const QgsDataProvider::ProviderOptions &options, QgsDataProvider::ReadFlags flags )
{
  ......
  mDataProvider = qobject_cast<QgsVectorDataProvider *>( QgsProviderRegistry::instance()->createProvider( provider, mDataSource, options, flags ) );
  ......
  if ( mDataProvider->capabilities() & QgsVectorDataProvider::ReadLayerMetadata )
  {
    // we combine the provider metadata with the layer's existing metadata, so as not to reset any user customizations to the metadata
    // back to the default if a layer's data source is changed
    QgsLayerMetadata newMetadata = mDataProvider->layerMetadata();
    // this overwrites the provider metadata with any properties which are non-empty from the existing layer metadata
    newMetadata.combine( &mMetadata );

    setMetadata( newMetadata );
    QgsDebugMsgLevel( QStringLiteral( "Set Data provider QgsLayerMetadata identifier[%1]" ).arg( metadata().identifier() ), 4 );
  }
  ......
}