How do you check your pokemons happiness?

In diamond, pearl, and platinum, there's a lady in the Eterna Pokemon centre who gives you the friendship checker poketch app, you tap a pokemon, and if no hearts appear, the pokemoon doesn't like you, if one heart, it's warming up to you, two hearts means it likes you, and two big hearts means it loves you, so if a Riolu, Eevee (if you want an Umbreon or Espeon), Sneasel, Happiny, etc., it must mean it is close to evolving.