If I have a terrific idea for an App and I approach someone to develop it, how would that negotiation take place?

I’m no expert in this, but I don’t think that “an idea” can be protected. To be protected, you would have to have developed the idea and demonstrated either a working prototype or process. The intellectual property is the design and build of the prototype or the process itself. Without that it’s just another good idea among the millions that occur every day.

So my best advice would be to discuss the idea of a partnership with the app developer that you know (and trust?) with the general understanding that you can provide process ideas and branches as well as other specifications dealing with the app, and the developer will provide the necessary coding, user interface (again, with your input) databases and forms required.

I don’t think that your idea can be protected until it has come together with the code, database (or whatever other information requirements you have), screens and other interfaces, and the app is demonstrated to have some kind of utility (or entertainment) value.

If you want to get paid, do some work.
Ideas by themselves are not worth anything. Implementation is worth something. “Intellectual property” is an odious concept ab initio, but until you have something tangible worked out you don’t actually have any “intellectual property. That is, you have absolutely no way of knowing that someone else in the world isn’t implementing “your” idea in code right now.
These “people who have made apps” are probably not sitting around twiddling their thumbs, waiting for someone to bring them an idea. I’ll bet they have plenty of ideas of their own. I know that personally, I have many more ideas than I can ever build into code myself; I give them away for free, because that’s what they are worth.

If you don’t want to learn to write apps (it’s not so hard, really) yourself, then you need to pay someone for the time and effort they will expend in developing your idea, or else give it away publicly and hope someone runs with it. No one with any sense will pay you for the opportunity to do work. Do you want someone without sense to work on your app?

Your idea isn’t doing any good sitting in your head. You are going to have to eventually trust someone or download Xcode and buy a bunch of books. The odds are someone has already had the idea.

You will have a hard time finding someone that will do it for free for 50% of the company. Nearly impossible if you don’t actually tell them your idea first.

Feel free to send me a PM with your idea and I can give you a ballpark figure of what it would cost to actually make it. I have no interest in stealing your idea and I am to busy to bother stealing it.