What's the changes between developing for the iPhone and the iPhone 4?

Hey, I'm working on an iPhone app but I've heard from some people that it's a size difference between the iPhone and the iPhone 4 and if it's not iPhone 4 committable to use the retain display it will be rejected by Apple.

So my questions is: What size does my app need to be in since it's not 320 x 480 anymore. And will the app automatically shrink the size 开发者_StackOverflow中文版down when it's used on an older iPhone or do I have to do something more with it?

Hope this makes sense to you guys!

Thank you in Advance

It's actually a UI design question. Luckily Apple has made it quit easy for developers to upgrade their apps for iPhone 4's retina display. All you need to do is follow a specific naming convention.

To all your UI files in your project (yes, those PNG files), you should make a new set of copies of all of them, doubling heights and widths (e.g. 320 x 480 => 640 x 960), and rename them in the following way:

• myFirstImage.png => myFirstImage@2x.png

And that's all, hope it helps.

Edited: there is one exception. The icon files and the artwork file. It is slightly more complicated. You should download the iTunes_Connect_Developer_Guide and take a look at related sections.