Dressed in a black T-shirt and hoodie, he talked a little like a runaway train, sentences running into sentences. “What’s annoying about it is, like, if things keep going the way they are going, I might well get it at some point,” he said, chuckling at the absurdity of the situation. “I don’t know what that makes me feel, to be honest. It’s just, like, odd. I read somewhere that they said I was a perfect person to do it with because I don’t have social media, so I can’t see it and respond immediately.”

Asked about his dressing room, Mr. Radcliffe gamely held up his monitor for a guided tour. The panorama included a rumpled bed; a handmade card from Grant Shaffer, the husband of his co-star Alan Cumming; and a pile of fan mail. How much does he receive a day?

“About a foot, probably,” he said. He tries to respond to it all.

Over the course of 75 minutes, Mr. Radcliffe spoke about his abiding love for “The Simpsons,” his upcoming turn as a “very posh, stupid prince” in the movie version of “Unbreakable Kimmy Schmidt” and his psychological response mechanism to the tenacious characterization of child actors as nightmares.

“Knowing that is what people think about young actors made me counteract that to the point where you could be quite rude to me and I would not notice,” said Mr. Radcliffe, who is now 30. “I would be so paranoid that you could say whatever you liked.” It had, he added, given him an excess of sympathy for celebrities like Justin Bieber.