xcode3换xcode4，three20项目问题解决办法

http://three20.info/article/2011-03-10-Xcode4-Support

首先把Three20.xcodeProj编译一下,然后安装下面方法

Xcode 4 Transition Guide

Apple is pushing for Xcode 4 to be the primary development
environment and, as a result, many of us will transition from Xcode
3.2 to Xcode 4 over the coming weeks. This guide has been put
together by the Three20 team in order to help you migrate your apps
to Xcode 4 successfully.

What you need to do

For existing projects

If you want to start using Xcode 4 with an existing project made
using Xcode 3.2.#, all you need to do to update your project is run
ttmodule again like so:

> python three20/src/scripts/ttmodule.py -p path/to/your/project/project.xcodeproj Three20 --xcode-version=4

This will add the following two header search paths to your
project:

"$(BUILT_PRODUCTS_DIR)/../three20"

"$(BUILT_PRODUCTS_DIR)/http://www.cnblogs.com/three20"

If you do not want to use ttmodule to do this, you can do it by
hand. Simply modify your target’s settings and add both values to
the “Header Search Paths” value. Please ensure that you’ve added
the quotes around the paths. This is in case there are any spaces
in your path. Without the quotes, Xcode will see the space and
think you’re passing two paths instead of one.

We specify both flags before the existing search path because we
want to prioritize these folders over the other one.

For new projects

Please use the ttmodule script to add Three20 to your project. We
do not currently directly support workspaces.

Hey, listen!

Before you transition to Xcode 4,
please clear
out the three20/Build directory of everything
except the ignoreme file. This is to ensure that you don’t
accidentally use an old version of one of the Three20 headers.

The Dirty Details

Build output is now, by default, placed in a “derived data
location”. This goes against a basic assumption the Three20
ecosystem makes about the build environment: that it controls where
its build output goes. As a result, when you open an Xcode 3.2.#
project in Xcode 4, it will build your Three20 dependencies in a
new “derived data location”. When your app then goes to look for
the Three20 headers in ../three20/Build/Products/three20,
it won’t find the files. If it does, it’s only because you probably
still have files leftover from being built by Xcode 3.2.#.

We solved this problem by adding some harmless additional search
paths and doing conditional checks of the Xcode version and build
type where necessary.