总是显示R.id.main cannot be resolved

这是代码。。

package p.progress;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;
import android.R;
public class ProgressbarActivity extends Activity {
    /** Called when the activity is first created. */

    private ProgressBar firstBar =null;
    private ProgressBar secondBar =null;
    private Button myButton =null;
    private int i =0 ;
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        firstBar = (ProgressBar)findViewById(R.id.firstBar);
        secondBar =(ProgressBar)findViewById(R.id.secondBar);
        myButton =(Button)findViewById(R.id.myButton);
        myButton.setOnClickListener(new ButtonListener());
        System.out.println(firstBar.getMax());
    }
    class ButtonListener implements OnClickListener{
     public void onClick(View v){
     if(i == 0){
     firstBar.setVisibility(View.VISIBLE);
     secondBar.setVisibility(View.VISIBLE);
     }
     else if (i<100)
     {
     firstBar.setProgress(i);
     firstBar.setSecondaryProgress(i + 10);
     secondBar.setProgress(i);
     }
     else{
     firstBar.setVisibility(View.GONE);
     secondBar.setVisibility(View.GONE);
     }
     i = i +10;
     }

    }
}

main.xml
中查看了没有错误，怎么办？？ --------------------编程问答-------------------- import android.R;去掉

PS:有android版块 --------------------编程问答-------------------- 恩同楼上我在编程时也遇见过相同的情况不过删除了 import android.R以后就一切正常了

补充：Java ,  Java相关