Count search results in Lucene.Net -

i'm new lucene , want count occurences of search word in index. saw should use like:

 indexreader reader = ....... 

termdocs termdoc = reader.termdocs();

termdoc.seek(new term("my_field", mstrsearchfor));

int occurencecount = termdoc.freq();

i can't seem create indexreader start.

fsdirectory directory = fsdirectory.open(new system.io.directoryinfo("c:\\temp\\")); indexreader reader = indexreader.open(directory, true);