AppCompat is
a library project. You need to reference the library project in your android project.
https://developer.android.com/tools/support-library/setup.html
Check the topic Adding libraries with resources.
1、导入某个现有工程文件夹后，出现R资源不能resolve的错误，导致程序无法编译运行，此时右键->properties->android，看最上面的taget又没有选择对，勾选当前可选的最高那个版本（即你本机已经安装的最高版本的SDK），点击apply，错误解决。
2、style.xml里出现样式无法识别：
error: Error retrieving parent for item: No resource found that matches the given name ‘Theme.AppCompat.Light‘.
也包括其他样式的此类错误，是因为：
|
8
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https://developer.android.com/tools/support-library/setup.html Check the topic Adding libraries with resources. |
|
8
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https://developer.android.com/tools/support-library/setup.html Check the topic Adding libraries with resources. |
原文：http://blog.csdn.net/jiadebin890724/article/details/25166045