xxx cannot be resolved or is not a field

参考文章：http://stackoverflow.com/questions/3296047/id-cannot-be-resolved-or-is-not-a-field-error

【1】Look at your

import

statements
at the top. If you are saying

import
android.R

, then there that is a problem. It might not be the only one as these 'R' errors can be tricky, but it would definitely definitely at least part of the problem.

如果有android.R，则删去import android.R。

【2】If that doesn't fix it, make sure your eclipse plugin(ADT) and your android SDK are fully up to date, remove the project from the emulator/phone by manually deleting it from the OS, and clean the project (Launch Eclipse->Project->Clean...). Sounds silly
to make sure your stuff is fully up to date, but the earlier versions of the ADT and SDK has a lot of annoying bugs related to the R files that have since been cleared up.

确认Build Automatically，再试试Launch Eclipse->Project->Clean。

【3】Just FYI, the stuff that shows up in the R class is generated from the stuff in your project res (aka resources) folder. The R class allows you to reference a resource (such as an image or a string) without having to do file operations all over the place.
It does other stuff too, but that's for another answer. Android OS uses a similar scheme - it has a resources folder and the class android.R is the way to access stuff in the android resources folder. The problem arises when in a single class you are using
both your own resources, and standard android resources. Normally you can say

import

at
the top, and then reference a class just using the last bit of the name (for example,

import
java.util.List

allows you to just write

List

in
your class and the compiler knows you mean

java.util.List

).
When you need to use two classes that are named the same thing, as is the case with the auto-generated R class, then you can import one of them and you have to fully qualify the other one whenever you want to mean it. Typically I import the R file for my project,
and then just say android.R.whatever when I want an android resource.

Also, to reiterate Andy, don't modify the R file automatically. That's not how it's meant to be used.

最后试试File->Refresh和File->Save。

确保语法没有错误。