Here is my solution
selectionObjectTemp = Sketchup.active_model.selection.to_a
if selectionObjectTemp.length == 0
selectionTemp = nil
else
selectionTemp = selectionObjectTemp
end
if @definitions[definitionAImporter]
definition = @definitions[definitionAImporter]
else
composantPath = File.join(@libPath,"#{definitionAImporter}.skp")
if File.exist?(composantPath)
definition = @definitions.load composantPath
else
UI.messagebox "le chemin n'existe pas; #{composantPath}"
end
end
if selectionTemp != nil
selectionTemp.each{|entitie|
if entitie.is_a? Sketchup;;ComponentInstance
entitie.definition = definition
end
}
end