downgrading iPhone 3GS iOS4 to OS3

I'm working on an iphone project for OS3.1.3. I updated my iPhone to iOS4 and now I can't test my project on my iPhone anymore. I tried downgrading but get 开发者_StackOverflow"device not eligible"

What should I do now?

If I download latest XCode SDK4 will I be able to recreate my app so that it runs both on OS3 and OS4 ? It has no specific os4 features.. it should just run on both and want to test it on real iphone with os4..

Greets

First of all, downgrading your phone won't work. at least not with the "official" approach. I think once there is a Jailbreak for iOS4, downgrading your phone should be possible again.

Secondly, Creating an iOS app with XCode SDK4 that runs on your 3.x devices is no problem at all:

Just set the "iPhone OS Deployment Target" Value (Target -> Info -> Build) to "iPhone OS 3.0"

You can build with SDK4 and still target older devices running iOS 3.2 or earlier. How to do this is covered in detail in this other question here.

You can downgrade your phone OS, that's covered in this question over here.

But really the best approach is to update Xcode, compile with SDK4 and support earlier iOS versions as well.

I'm in the same situation.

What is the best ? 1 Upgrade to SDK4 and still target on IOS 3.xx . Will iPhone ios 3.1.3 users be able to download apps built with SDK4 . I don't think so. 2 Downgrade ios4 to ios3 and still work with SDK3.

PS : Someone suggested to get the lastest SDK

You can downgrade iPhones, iPod touches and iPads.

Instructions are here. If for instance you're downgrading a second generation iPod Touch from iOS4 to iOS3.1.3 you'll need the iPod2,1_3.1.3_7E18_Restore.ipsw firmware. A Google search will bring these things up.

Some downgrading references ask you to modify a "hosts" file. I don't think this is necessary, I downgraded from iOS4.2 to iOS3.0 (and to iOS2.0 for fun) without having to do this.

Good luck.