title: Unable to Destroy activity Error
body: <p>Im new in android... when i press back button it gives me the below Error...<code>12-01 11:10:07.952: E/AndroidRuntime(3171): FATAL EXCEPTION: main
  12-01 11:10:07.952: E/AndroidRuntime(3171): java.lang.RuntimeException: Unable to destroy activity {com.example.IranNara/com.example.IranNara.FirstPage}: java.lang.NullPointerException
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3655)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3673)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.app.ActivityThread.access$2900(ActivityThread.java:125)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.os.Handler.dispatchMessage(Handler.java:99)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.os.Looper.loop(Looper.java:123)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.app.ActivityThread.main(ActivityThread.java:4627)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at java.lang.reflect.Method.invokeNative(Native Method)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at java.lang.reflect.Method.invoke(Method.java:521)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at dalvik.system.NativeStart.main(Native Method)
  12-01 11:10:07.952: E/AndroidRuntime(3171): Caused by: java.lang.NullPointerException
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at com.example.IranNara.FirstPage.onDestroy(FirstPage.java:133)
  12-01 11:10:07.952: E/AndroidRuntime(3171):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3642)
  </code></p>
  
  <p>and my activity code is:</p>
  
  <pre><code>    Button Nara;
  SQLiteDatabase mydb;
  String Text="";
  //private static String DBNAME = "PDA";    
  private static String TABLE = "Users";
  public static Integer StartFlag;
  //LinearLayout linearL;
  //public static String storedPersonelNo = "";
  
  @Override
    public void onCreate(Bundle savedInstanceState) {
  
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_xml);                  
        Nara = (Button)findViewById(R.id.btnNara);
        StartFlag =0;
  
        final NaraAdapter mydb = new NaraAdapter(this);         
        mydb.createDatabase();       
        mydb.open();
        //System.out.println("My DB is:::: "+mydb);
  
  
        //For Login
        final Dialog dialog = new Dialog(FirstPage.this);
        dialog.setContentView(R.layout.login);
        dialog.setTitle("Login");
        final  EditText editTextUserName=(EditText)dialog.findViewById(R.id.editTextUserNameToLogin);
        final  EditText editTextPassword=(EditText)dialog.findViewById(R.id.editTextPasswordToLogin); 
  
       //----------for entering on Exit Button------------------------------------------------------------------------------------------
        if( getIntent().getBooleanExtra("Exit", false)){
              finish();
              return;
          }
       //-----------------------------------------------------------------------------------------------------------------------//********click on IranNara Button
  
  
  Nara.setOnClickListener(new View.OnClickListener() {
  
                  //Click on Cancel Button
                  public void onClick(View v) 
                  {      
                     Button btnLogin=(Button)dialog.findViewById(R.id.buttonLogin);
                     Button Cancel = (Button)dialog.findViewById(R.id.btncancel);
                     dialog.show();
  
                     Cancel.setOnClickListener(new View.OnClickListener() {
                      public void onClick(View v) {
                          dialog.dismiss();
                          editTextPassword.setText("") ;
                      }});
  
  
                     //Click on Login Button 
                     btnLogin.setOnClickListener(new View.OnClickListener() {
                      public void onClick(View v) {
                          // get The User name and Password
                          String userName=editTextUserName.getText().toString();
                          String password=editTextPassword.getText().toString();
                          // fetch the Password
  
                          String storedPassword = getSinlgeEntry(userName,1);
                          System.out.println("storedPassword:"+storedPassword);
  
                          // check if the Stored password matches with  Password entered by user
                          if(password.equals(storedPassword))
                          {
                              Toast.makeText(FirstPage.this, "Congrats: Login Successfull", Toast.LENGTH_LONG).show();
                              // Entered to Messages
                              String storedPersonelNo = getSinlgeEntry(userName,2);
                              Intent Startmain    = new Intent(FirstPage.this, Main.class);
                              Startmain.putExtra("PersonelNumber", storedPersonelNo);
                             // SharedPreferences settings = getSharedPreferences(storedPersonelNo, 0);
                              dialog.dismiss();
                              StartFlag=1;
                              startActivityForResult(Startmain, 0);                           
                          }
                          else
                          {
                              Toast.makeText(FirstPage.this, "User Name or Password does not match", Toast.LENGTH_LONG).show();
                            }
                        }
                     });
                  }
              });     
  
  
  }
  </code></pre>
  
  <p>//--------------------------------------------------------------------METHODS---------------------------------------------------------------------------------------------------------------</p>
  
  <pre><code>    public String getSinlgeEntry(String userName,Integer n)
  {  
      NaraDatabaseHandler DH = new NaraDatabaseHandler(this);         
      mydb = DH.getReadableDatabase();
      //System.out.println("My DB is:::: "+mydb);
      Cursor cursor=mydb.query(TABLE, null, " UserName=?", new String[]{userName}, null, null, null);
      if(cursor.getCount()&lt;1) 
      {   
          cursor.close();  
          return "NOT EXIST";
      }
      cursor.moveToFirst();
      if (n==1){
      Text= cursor.getString(cursor.getColumnIndex("Password"));}
      if(n==2){
      Text= cursor.getString(cursor.getColumnIndex("PersonelNo"));}
      cursor.close();
  
      return Text;
  }   
  
  @Override
  protected void onDestroy() {
      super.onDestroy();
      mydb.close();
      //StartFlag = null;
  
  }`
  </code></pre>