public class PrayMain extends ListActivity implements OnClickListener {
 
 protected SQLiteDatabase pray_db1;
 protected Cursor pray_cursor1;
 protected ListAdapter pray_adapter1;
 protected EditText txt_add_category;
// protected Button btn_add_category;
 
 //protected Button btn_main_bible;
 public void onCreate(Bundle savedInstanceState) {
     
        super.onCreate(savedInstanceState);
       
        // Error가 남 원인이 무엇인지 모르겠음
        //setContentView(R.layout.pray_main);
      
        pray_db1 = (new DataBaseHelper(this)).getWritableDatabase();
              
        //SimpleCursorAdapter에 작업하는 테이블에 반드시 _id필드가 있어야 한다
        pray_cursor1 = pray_db1.rawQuery("SELECT _id, category from PRAY_category order by _id asc",null);

  pray_adapter1 = new SimpleCursorAdapter(this,
           R.layout.pray_main,
           pray_cursor1,
           new String[] {"category"},
           new int[] {R.id.pray_category});
  setListAdapter(pray_adapter1);
  
  Button btn_add_category = (Button)findViewById(R.id.btn_category_insert);
  btn_add_category.setOnClickListener(this); <--------------------------------------------------------------------------에러나는 부분

 }