Исключение Null-указателя при запуске активности запуска в android

Question

Я пытался сделать плеером Android-плеер для воспроизведения некоторых видеофайлов с SD-карты. для этого я написал два класса Main.java и VideoSelector.java, но при запуске моего приложения он показывает исключение с нулевым указателем. Пожалуйста, помогите мне исправить эту ошибку

Main.java

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 
import android.widget.VideoView; 

public class Main extends Activity { 

    private VideoView m_vvPlayer; 

    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     m_vvPlayer = (VideoView) findViewById(R.id.vvMain); 
     Button btnSelectFile = (Button) findViewById(R.id.btnSelectFile); 
     btnSelectFile.setOnClickListener(new View.OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       Intent i = new Intent(); 
       i.setClass(v.getContext(), VideoSelector.class); 
       startActivityForResult(i, 0); 
      } 
     }); 
    } 

    @Override 
    protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
     super.onActivityResult(requestCode, resultCode, data); 
     if (RESULT_OK == resultCode) { 
      Bundle bd = data.getExtras(); 
      String path = bd.getString(VideoSelector.FILE_PATH); 
      m_vvPlayer.setVideoPath(path); 
      m_vvPlayer.start(); 
     } 
    } 
} 

VideoSelector.java

import android.app.ListActivity; 
import android.content.ContentResolver; 
import android.content.Intent; 
import android.database.Cursor; 
import android.os.Bundle; 
import android.provider.MediaStore; 
import android.view.View; 
import android.widget.ListView; 
import android.widget.SimpleCursorAdapter; 

public class VideoSelector extends ListActivity { 

    public static final String FILE_PATH = "FILE_PATH"; 
    public void onCreate(Bundle icicle) 
    { 
     super.onCreate(icicle); 
     init(); 
    } 

    public void init() { 
     setContentView(R.layout.video_selector); 

     MakeCursor(); 

     // Map Cursor columns to views defined in media_list_item.xml 
     SimpleCursorAdapter adapter = new SimpleCursorAdapter(
       this, 
       android.R.layout.simple_list_item_1, 
       mCursor, 
       new String[] { MediaStore.Video.Media.TITLE}, 
       new int[] { android.R.id.text1 }); 

     setListAdapter(adapter); 
    } 

    @Override 
    protected void onListItemClick(ListView l, View v, int position, long id) 
    { 
     String filePath = mCursor.getString(mCursor.getColumnIndex(MediaStore.Video.Media.DATA)); 
     mCursor.moveToPosition(position); 
     Intent result = new Intent(); 
     result.putExtra(FILE_PATH, filePath); 
     setResult(RESULT_OK, result); 
     finish(); 
    } 

    private void MakeCursor() { 
     String[] cols = new String[] { 
       MediaStore.Video.Media._ID, 
       MediaStore.Video.Media.TITLE, 
       MediaStore.Video.Media.DATA, 
       MediaStore.Video.Media.MIME_TYPE, 
       MediaStore.Video.Media.ARTIST 
     }; 
     ContentResolver resolver = getContentResolver(); 
     if (resolver == null) { 
      System.out.println("resolver = null"); 
     } else { 
      mSortOrder = MediaStore.Video.Media.TITLE + " COLLATE UNICODE"; 
      mWhereClause = MediaStore.Video.Media.TITLE + " != ''"; 
      mCursor = resolver.query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, 
       cols, mWhereClause , null, mSortOrder); 
     } 
    } 

    private Cursor mCursor; 
    private String mWhereClause; 
    private String mSortOrder; 
} 

LogCat

08-04 11:28:18.862: I/ApplicationPackageManager(12180): cscCountry is not German : INS 
08-04 11:28:18.933: W/dalvikvm(12180): threadid=1: thread exiting with uncaught exception (group=0x40018578) 
08-04 11:28:18.933: E/AndroidRuntime(12180): FATAL EXCEPTION: main 
08-04 11:28:18.933: E/AndroidRuntime(12180): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.Main}: java.lang.NullPointerException 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.os.Handler.dispatchMessage(Handler.java:99) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.os.Looper.loop(Looper.java:130) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.app.ActivityThread.main(ActivityThread.java:3687) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at java.lang.reflect.Method.invokeNative(Native Method) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at java.lang.reflect.Method.invoke(Method.java:507) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at dalvik.system.NativeStart.main(Native Method) 
08-04 11:28:18.933: E/AndroidRuntime(12180): Caused by: java.lang.NullPointerException 
08-04 11:28:18.933: E/AndroidRuntime(12180): at com.example.test.Main.onCreate(Main.java:22) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
08-04 11:28:18.933: E/AndroidRuntime(12180): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 
08-04 11:28:18.933: E/AndroidRuntime(12180): ... 11 more 

Answer 1

В файле activity_main.xml нет ресурсов, например R.id.btnSelectFile