I don't think you need one if you already do iOS app development. You're already in good shape to just jump in. You know Objective-C. I don't see the concern he

I don't think you need one if you already do iOS app development. You're already in good shape to just jump in. You know Objective-C. I don't see the concern here unless you're the world's worst iOS developer. What do you want to learn, exactly? Try Pluralsight.com. That's where I got started with C#.