android R文件不更新问题

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文件里边的id不产生start ，stop，exit的属性值

clean一下，然后看看有没有错误提示

project clean 过，不产生start stop exit 属性

产生这种问题一般都是xml文件有错误编译不过去，看下你的xml文件是不是有问题。

看你出错的文件导入的(检查import)R是否是你需要的，很有可能是导入了android的R，将其删除然后重新导入带你自己包名的R。
例如如果是这个：

import android.R;

将其删除，换为你自己的：

 import com.XXXX.XXXX.R;

clean and rebuild