Do not modify the R class. The error means there‘s something syntactically wrong with your XML layouts and R cannot be auto-generated. Try looking there and post the xml code you‘re not sure about, if any.
Edit : also: remove "import android.R" from imports at top of file (if there)
我的解决方案是去掉了import android.R这一行，增加了现有的包名import com.example.avtivitytest.R;
//import android.R; import com.example.avtivitytest.R;