xxx cannot be resolved or is not a field

1.protected void onCreate(Bundle savedInstanceState) {
2. // TODO Auto-generated method stub
3. super.onCreate(savedInstanceState);
4. setContentView(R.layout.first_layout);

5. }

此代码会报
first_layout cannot be resolved or is not a field

解决办法:

在第四行前加上完整包名，例如：

改为：com.example.activitytest.R.layout.first_layout