关于android R文件不更新问题，已勾选自动更新

MainActivity.java

 package com.example;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        switch(item.getItemId()){
        case R.id.start:
        case R.id.stop:
            invalidateOptionsMenu();
            break;
        case R.id.exit:
            finish();
            break;
            default:
                break;  
    }
        Toast.makeText(MainActivity.this, item.getTitle()+"被单击了", 1000).show();
        return true;
    }
    public boolean onPrepareOptionsMenu(Menu menu){
        super.onPrepareOptionsMenu(menu);
        MenuItem start=menu.findItem(R.id.start);
        MenuItem stop=menu.findItem(R.id.stop);

        boolean flag = false;
        start.setEnabled(flag);
        stop.setEnabled(!flag);
        flag=!flag;
        return true;

        }
}



/* AUTO-GENERATED FILE. DO NOT MODIFY.
 *
This class was automatically generated by the
aapt tool from the resource data it found. It
should not be modified by hand. */

package com.example;

public final class R {
 public static final class attr {
 }
 public static final class dimen {
 /** Default screen margins, per the Android Design guidelines. 
     Example customization of dimensions originally defined in res/values/dimens.xml
     (such as screen margins) for screens with more than 820dp of available width. This
     would include 7" and 10" devices in landscape (~960dp and ~1280dp respectively).

     */
    public static final int activity_horizontal_margin=0x7f040000;
    public static final int activity_vertical_margin=0x7f040001;
}
public static final class drawable {
    public static final int ic_launcher=0x7f020000;
}
public static final class id {
    public static final int action_settings=0x7f080000;
}
public static final class layout {
    public static final int activity_main=0x7f030000;
}
public static final class menu {
    public static final int main=0x7f070000;
}
public static final class string {
    public static final int action_settings=0x7f050002;
    public static final int app_name=0x7f050000;
    public static final int hello_world=0x7f050001;
}
public static final class style {
    /** 
    Base application theme, dependent on API level. This theme is replaced
    by AppBaseTheme from res/values-vXX/styles.xml on newer devices.


        Theme customizations available in newer API levels can go in
        res/values-vXX/styles.xml, while customizations related to
        backward-compatibility can go here.


    Base application theme for API 11+. This theme completely replaces
    AppBaseTheme from res/values/styles.xml on API 11+ devices.


API 11 theme customizations can go here. 
    Base application theme for API 14+. This theme completely replaces
    AppBaseTheme from BOTH res/values/styles.xml and
    res/values-v11/styles.xml on API 14+ devices.


API 14 theme customizations can go here. 
/
 public static final int AppBaseTheme=0x7f060000;
 /* Application theme. 
 All customizations that are NOT specific to a particular API-level can go here. 
 */
 public static final int AppTheme=0x7f060001;
 }
 }

R文件id里不产生start ，stop ，exit的相关数据