void QgsGraduatedSymbolRendererV2::startRender( QgsRenderContext& context, const QgsFields& fields )
{
  // find out classification attribute index from name
  mAttrNum = fields.fieldNameIndex( mAttrName );

  if ( mAttrNum == -1 )
  {
    mExpression.reset( new QgsExpression( mAttrName ) );
    mExpression->prepare( fields );
  }

  QgsRangeList::iterator it = mRanges.begin();
  for ( ; it != mRanges.end(); ++it )
  {
    it->symbol()->startRender( context, &fields );

    if ( mRotation.data() || mSizeScale.data() )
    {
      QgsSymbolV2* tempSymbol = it->symbol()->clone();
      tempSymbol->setRenderHints(( mRotation.data() ? QgsSymbolV2::DataDefinedRotation : 0 ) |
                                 ( mSizeScale.data() ? QgsSymbolV2::DataDefinedSizeScale : 0 ) );
      tempSymbol->startRender( context, &fields );
      mTempSymbols[ it->symbol()] = tempSymbol;
    }
  }
}

QgsSymbolV2* QgsGraduatedSymbolRendererV2::symbolForValue( double value )
{
  for ( QgsRangeList::iterator it = mRanges.begin(); it != mRanges.end(); ++it )
  {
    if ( it->lowerValue() <= value && it->upperValue() >= value )
      return it->symbol();
  }
  // the value is out of the range: return NULL instead of symbol
  return NULL;
}

void QgsGraduatedSymbolRendererV2::startRender( QgsRenderContext& context, const QgsVectorLayer *vlayer )
{
  // find out classification attribute index from name
  mAttrNum = vlayer ? vlayer->fieldNameIndex( mAttrName ) : -1;

  mRotationFieldIdx  = ( mRotationField.isEmpty()  ? -1 : vlayer->fieldNameIndex( mRotationField ) );
  mSizeScaleFieldIdx = ( mSizeScaleField.isEmpty() ? -1 : vlayer->fieldNameIndex( mSizeScaleField ) );

  QgsRangeList::iterator it = mRanges.begin();
  for ( ; it != mRanges.end(); ++it )
  {
    it->symbol()->startRender( context, vlayer );

    if ( mRotationFieldIdx != -1 || mSizeScaleFieldIdx != -1 )
    {
      QgsSymbolV2* tempSymbol = it->symbol()->clone();
      tempSymbol->setRenderHints(( mRotationFieldIdx != -1 ? QgsSymbolV2::DataDefinedRotation : 0 ) |
                                 ( mSizeScaleFieldIdx != -1 ? QgsSymbolV2::DataDefinedSizeScale : 0 ) );
      tempSymbol->startRender( context, vlayer );
      mTempSymbols[ it->symbol()] = tempSymbol;
    }
  }
}

QgsFeatureRendererV2* QgsGraduatedSymbolRendererV2::create( QDomElement& element )
{
  QDomElement symbolsElem = element.firstChildElement( "symbols" );
  if ( symbolsElem.isNull() )
    return NULL;

  QDomElement rangesElem = element.firstChildElement( "ranges" );
  if ( rangesElem.isNull() )
    return NULL;

  QgsSymbolV2Map symbolMap = QgsSymbolLayerV2Utils::loadSymbols( symbolsElem );
  QgsRangeList ranges;

  QDomElement rangeElem = rangesElem.firstChildElement();
  while ( !rangeElem.isNull() )
  {
    if ( rangeElem.tagName() == "range" )
    {
      double lowerValue = rangeElem.attribute( "lower" ).toDouble();
      double upperValue = rangeElem.attribute( "upper" ).toDouble();
      QString symbolName = rangeElem.attribute( "symbol" );
      QString label = rangeElem.attribute( "label" );
      bool render = rangeElem.attribute( "render", "true" ) != "false";
      if ( symbolMap.contains( symbolName ) )
      {
        QgsSymbolV2* symbol = symbolMap.take( symbolName );
        ranges.append( QgsRendererRangeV2( lowerValue, upperValue, symbol, label, render ) );
      }
    }
    rangeElem = rangeElem.nextSiblingElement();
  }

  QString attrName = element.attribute( "attr" );

  QgsGraduatedSymbolRendererV2* r = new QgsGraduatedSymbolRendererV2( attrName, ranges );

  QString attrMethod = element.attribute( "graduatedMethod" );
  if ( attrMethod.length() )
  {
    if ( attrMethod == graduatedMethodStr( GraduatedColor ) )
      r->setGraduatedMethod( GraduatedColor );
    else if ( attrMethod == graduatedMethodStr( GraduatedSize ) )
      r->setGraduatedMethod( GraduatedSize );
  }


  // delete symbols if there are any more
  QgsSymbolLayerV2Utils::clearSymbolMap( symbolMap );

  // try to load source symbol (optional)
  QDomElement sourceSymbolElem = element.firstChildElement( "source-symbol" );
  if ( !sourceSymbolElem.isNull() )
  {
    QgsSymbolV2Map sourceSymbolMap = QgsSymbolLayerV2Utils::loadSymbols( sourceSymbolElem );
    if ( sourceSymbolMap.contains( "0" ) )
    {
      r->setSourceSymbol( sourceSymbolMap.take( "0" ) );
    }
    QgsSymbolLayerV2Utils::clearSymbolMap( sourceSymbolMap );
  }

  // try to load color ramp (optional)
  QDomElement sourceColorRampElem = element.firstChildElement( "colorramp" );
  if ( !sourceColorRampElem.isNull() && sourceColorRampElem.attribute( "name" ) == "[source]" )
  {
    r->setSourceColorRamp( QgsSymbolLayerV2Utils::loadColorRamp( sourceColorRampElem ) );
    QDomElement invertedColorRampElem = element.firstChildElement( "invertedcolorramp" );
    if ( !invertedColorRampElem.isNull() )
      r->setInvertedColorRamp( invertedColorRampElem.attribute( "value" ) == "1" );
  }

  // try to load mode
  QDomElement modeElem = element.firstChildElement( "mode" );
  if ( !modeElem.isNull() )
  {
    QString modeString = modeElem.attribute( "name" );
    if ( modeString == "equal" )
      r->setMode( EqualInterval );
    else if ( modeString == "quantile" )
      r->setMode( Quantile );
    else if ( modeString == "jenks" )
      r->setMode( Jenks );
    else if ( modeString == "stddev" )
      r->setMode( StdDev );
    else if ( modeString == "pretty" )
      r->setMode( Pretty );
  }

  QDomElement rotationElem = element.firstChildElement( "rotation" );
  if ( !rotationElem.isNull() && !rotationElem.attribute( "field" ).isEmpty() )
  {
    for ( QgsRangeList::iterator it = r->mRanges.begin(); it != r->mRanges.end(); ++it )
    {
      convertSymbolRotation( it->symbol(), rotationElem.attribute( "field" ) );
    }
    if ( r->mSourceSymbol.data() )
    {
      convertSymbolRotation( r->mSourceSymbol.data(), rotationElem.attribute( "field" ) );
    }
  }
//.........这里部分代码省略.........