How do I show pictures online/offline for the 3Gs and iPhone4?

I have two pictures, one for 3GS,the other for iPhone4！And I want to show them on map with online and offline. The pictures can be show normally with 3GS, but for iPhone4, the picture just can be show normally on offline map, and for online map开发者_运维知识库 the picture will be multiply several times.

You should be able to add the "@2x" identifier to your file name. In other words "myImageAsset.png" for the regular version, and "myImageAsset@2x.png" for the iPhone 4 version. For more details, check out the "Supporting High-Resolution Screens" section of the Drawing and Printing Guide for iOS available inside Xcode.