He’s all for transparency — ­except when it comes to his own fundraising.

Mayor de Blasio resorted to virtually every excuse in the book Friday to explain why he had to raise funds for his federal political action committee from a Boston developer who’s trying to bolster his business in New York City.

It was left to reporters to come up with the identity of the developer since de Blasio — who once pledged to run the “most transparent” administration ever — refused to reveal it.

Brian Lehrer, usually the even-handed host of the mayor’s weekly call-in show on WNYC radio, pressed him for nearly 10 minutes on that shady turn of events.

“Are those the campaign-finance values you want voters to believe are progressive?” ­Lehrer asked.

De Blasio tried to get off the hook by claiming he’s all for campaign reforms but that he has to raise money through a system he abhors.

“Brian, we got to start coming to grips with this reality of how politics in America works . . .” the mayor said. “I don’t want to wake up in the morning having to fundraise.”

He also said he has to go where the money is because he has “very limited assets of my own” and doesn’t want to see “billionaires running our city and our country.”

Lehrer pointed out that there’s nothing in the law that would have prevented the mayor from disclosing that developer John Fish was behind a $5,000-a-plate fundraiser that morning in ­Boston.

De Blasio had no real answer for that, so he ducked by saying Fish’s name would have become public when the mayor’s Fairness PAC filed its donors.

But Lehrer wouldn’t let go.

“I’m not sure you answered my basic question,” he said.

After a couple minutes of back-and-forth, de Blasio finally declared testily:

“We tell the public. That’s all that matters. We tell the public every time we have to disclose. But look, in the end, everything I do, I am doing because I believe there’s a whole series of changes that we need to make and I need resources to get that message out.”

Fish’s company, Suffolk Construction, is looking to expand its New York City portfolio after building an apartment tower in Brooklyn Bridge Park.

The company recently hired Shola Olatoye, who resigned under fire last year as head of the city’s Housing Authority amid a lead-paint reporting scandal.

Two years ago, federal and state prosecutors declined to bring criminal charges against de Blasio for campaign-finance violations during his first term.

But Manhattan DA Cy Vance Jr. said that didn’t mean the mayor was being cleared.