How do you evolve Golbat into Crobat in Pokemon Diamond?

Answer 1

It needs to have its friendship to the maximum. this can be done by leveling it up, have it win some battles, give it a soothe bell (i don't know how it works, but i know somehow it does) or give it a type of berry that can raise happines (of course each of those berries i know of lower a certain stat some, so use it on one that shouldn't go down at all)also another way to boost friendship is to give 10 of each stat raising item

also, trading the Pokemon won't work like it does in Sapphire, ruby, emerald etc.

level it up to level 76 and teach it psychic, it worked for me