bool QgsVectorLayerLabelProvider::prepare( const QgsRenderContext &context, QSet<QString> &attributeNames )
{
QgsPalLayerSettings &lyr = mSettings;
const QgsMapSettings &mapSettings = mEngine->mapSettings();
QgsDebugMsgLevel( "PREPARE LAYER " + mLayerId, 4 );
if ( lyr.drawLabels )
{
if ( lyr.fieldName.isEmpty() )
{
return false;
}
if ( lyr.isExpression )
{
QgsExpression exp( lyr.fieldName );
if ( exp.hasEvalError() )
{
QgsDebugMsgLevel( "Prepare error:" + exp.evalErrorString(), 4 );
return false;
}
}
else
{
// If we aren't an expression, we check to see if we can find the column.
if ( mFields.lookupField( lyr.fieldName ) == -1 )
{
return false;
}
}
}
lyr.mCurFields = mFields;
if ( lyr.drawLabels || lyr.obstacle )
{
if ( lyr.drawLabels )
{
// add field indices for label's text, from expression or field
if ( lyr.isExpression )
{
// prepare expression for use in QgsPalLayerSettings::registerFeature()
QgsExpression *exp = lyr.getLabelExpression();
exp->prepare( &context.expressionContext() );
if ( exp->hasEvalError() )
{
QgsDebugMsgLevel( "Prepare error:" + exp->evalErrorString(), 4 );
}
Q_FOREACH ( const QString &name, exp->referencedColumns() )
{
QgsDebugMsgLevel( "REFERENCED COLUMN = " + name, 4 );
attributeNames.insert( name );
}
}
else
{
attributeNames.insert( lyr.fieldName );
}
}
void QgsAttributeTypeDialog::defaultExpressionChanged()
{
QString expression = mExpressionWidget->expression();
if ( expression.isEmpty() )
{
mDefaultPreviewLabel->setText( QString() );
return;
}
QgsExpressionContext context = mLayer->createExpressionContext();
if ( !mPreviewFeature.isValid() )
{
// get first feature
QgsFeatureIterator it = mLayer->getFeatures( QgsFeatureRequest().setLimit( 1 ) );
it.nextFeature( mPreviewFeature );
}
context.setFeature( mPreviewFeature );
QgsExpression exp = QgsExpression( expression );
exp.prepare( &context );
if ( exp.hasParserError() )
{
mDefaultPreviewLabel->setText( "<i>" + exp.parserErrorString() + "</i>" );
return;
}
QVariant val = exp.evaluate( &context );
if ( exp.hasEvalError() )
{
mDefaultPreviewLabel->setText( "<i>" + exp.evalErrorString() + "</i>" );
return;
}
QString previewText = val.toString();
QgsEditorWidgetFactory *factory = QgsEditorWidgetRegistry::instance()->factory( editorWidgetType() );
if ( factory )
{
previewText = factory->representValue( mLayer, mFieldIdx, editorWidgetConfig(), QVariant(), val );
}
mDefaultPreviewLabel->setText( "<i>" + previewText + "</i>" );
}