it's him or it's he?

[haze]

This is really confusing for me because most american movies use "it's him" and "it's her". But when i read a grammar book, it says there that it should be "it's he" and "it's she". "It's me" is also not acceptable by the book that i read. According to the book, "it's I" is the correct usage. Please let me know what is the correct usage for these. Thank you.

[Alan]

[It is + nominative pronoun] is generally regarded nowadays as hyperformal, and its use, even in written English, tends to be restricted to cases where the pronoun is followed by a relative clause, as in

It is I who am to blame.

contrasting with informal

(*)It's me that's to blame.

You are unlikely to be criticized by anybody - except the most ardent, dyed-in-the-wool purist - for saying, or even writing, It's me rather than It's I. Indeed the juxtaposition of inherently informal contraction it's with formal 'I' would even strike most speakers as rather ludicrous!