Robert Pattinson — he played the doomed Cedric Diggory in two Harry Potter films — has the starring role in How To Be.

According to staff members at the 12th Rhode Island International Film Festival, the greatest interest in any film at this year’s festival has been generated by the British film How to Be, which will play tomorrow.

The reason is not because it’s a soul-searching study of twentysomething angst in which a very unhappy young man who has just been dumped by his girlfriend moves back in with his parents, who are none too pleased by this turn of events, and tries to find himself.

No, it’s apparently because of rising British star Robert Pattinson in the lead role of the troubled Arthur. Pattinson won fans — and heartthrobs —as the doomed Cedric Diggory in two Harry Potter films. Come December he will star in Twilight as the vampire hero who falls in love with a human girl in the film version of the best-selling young adult book.

Well, he’s not exactly heartthrob material in writer-director Oliver Irving’s How to Be, a sometimes amusing, more often dreary exercise in frustration and unhappiness. As Arthur, Pattinson looks mostly unhappy and disheveled.

The film begins with Arthur’s childhood memory of his father burning all his “magical” toys in the backyard and proceeds on a downhill slope through most of the rest of the picture. A guitarist, he can’t quite finish a song. A volunteer at a community center, he’s asked to leave and not come back. An attempt to start a rock band with his best friend, an agoraphobic, doesn’t go well since the friend refuses to leave his apartment building.

Arthur believes his parents don’t like him and from what we see of his brittle mother (Rebecca Pidgeon), it seems at first that Arthur may be on to something. His testy relationship with her and his father make it seem as though there’s very little love on either side.

His woeful pleas to his ex-girlfriend to come back to him are embarrassing, although Arthur doesn’t realize it.

In his words, Arthur is going through “a quarter life crisis.” A bundle of anxiety, he says “I just feel unhappy all the time.”

It’s not until he reads a self-help book by Dr. Levi Ellington (a dry Powell Jones) that Arthur begins to believe he might be able to pull himself out of his grand funk. Arthur even imports Ellington from Canada to shadow him from dawn to dusk to see if the good doctor can put him on the right track and make him “be more normal.” The sight of Ellington turning up in the most unlikely places — a children’s restroom at a school, for instance — adds a light touch to the film.

Yet even though Pattinson is very good at playing a man who is all at sea in his life, the character of Arthur is so hopelessly frustrating and pathetic that his inability to move forward may be equally frustrating for the audience.

How to Be will be shown at 9:15 p.m. tomorrow at the Columbus Theatre, 270 Broadway, Providence, as part of the 12th Rhode Island International Film Festival. Tickets are $10 at the door. For a complete schedule of festival films, see rifilmfest.org.

** 1/2How to Be

Starring: Robert Pattinson, Rebecca Pidgeon, Powell Jones, Mike Pearce, Johnny White, Michael Irving, Alisa Arnah.

Rated: Not rated, contains profanity, adult themes.

mjanuson@projo.com