该代码说它找不到activity_main，但我已经在R.java中声明它

Question

正如您所见，我已导入R.java类，它包含activity_main。但setContent方法无法找到它。 这里是R.java类的定义：

/* 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.app2; 

    public final class R { 
    public static final class attr { 
    } 
    public static final class dimen { 
     /** Default screen margins, per the Android Design guidelines. 

     Customize dimensions originally defined in res/values/dimens.xml (such as 
     screen margins) for sw720dp devices (e.g. 10" tablets) in landscape here. 

     */ 
     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=0x7f080002; 
     public static final int button1=0x7f080000; 
     public static final int button2=0x7f080001; 
    } 
    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=0x7f050001; 
     public static final int app_name=0x7f050000; 
     public static final int hello_world=0x7f050002; 
    } 
    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; 
    } 
} 

这里是我的MainActivity.java。你能告诉我为什么会出现这个错误？

package com.example.app2; 

import android.R; 
import android.app.Activity; 
import android.content.Intent; 
import android.net.Uri; 
import android.os.Bundle; 
import android.widget.Button; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.view.Menu; 


public class MainActivity extends Activity { 
    Button button,bt1; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(android.R.layout.activity_main);//this line gives the error 
     addListenerOnButton(); 
     addListnerOnButton2(); 
    } 
public void addListenerOnButton() { 

    button = (Button) findViewById(R.id.button1); 

    button.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View arg0) { 

      Intent browserIntent = 
         new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.ischelper.in")); 
      startActivity(browserIntent); 

     } 
}); 


    } 
public void addListnerOnButton2() 
    { 
     bt1=(Button) findViewById(R.id.button2); 
     bt1.setOnClickListener(new OnClickListener(){ 

     @Override 
     public void onClick(View arg0) { 
      Intent browserIntent=new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.ischelper.in/pages/lectures")); 
      startActivity(browserIntent); 
     } 



    }); 
    } 
} 

Answer 1

替换此行：

import android.R; 

...这一行：

import com.example.app2.R;