フラグメント内のjavaクラスからメソッドを呼び出す方法は？

Question

こんにちは私はかなり新しいアンドロイドstuff.Firstly私はstackoverflow上の関連する質問から答えを見つけることができませんでした。私はNULLポインタを取得フラグメントイムを呼び出した後、私はフラグメントでこのメソッドを呼び出す必要がありactivity.ButでgetAllContactsメソッドを呼び出していたエラーが、ありません

 public class DbHelper extends SQLiteOpenHelper { 

     public static final String DB_NAME = "emergencydb"; 
     public static final int DB_VERSION = 2; 

     public DbHelper(Context context) { 
      super(context, DB_NAME, null, DB_VERSION); 
     } 

     @Override 
     public void onCreate(SQLiteDatabase db) { 
      // db.execSQL(UserDb.getSql()); 
      db.execSQL(ContactDb.getSql()); 
      Log.v("DatabaseCr", "OLUSTU"); 
      // db.execSQL(UserMessages.getSql()); 
     } 

     @Override 
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
      db.execSQL("DROP TABLE IF EXISTS " + ContactDb.TABLE_NAME); 
      onCreate(db); 
     } 

     @Override 
     public void onOpen(SQLiteDatabase db) { 
      // Foreign key desteğini açmak için 
      super.onOpen(db); 

     } 



     public List<Contact> getAllContacts() { 
     List<Contact> contacts = new ArrayList<Contact>(); 
      SQLiteDatabase db = this.getReadableDatabase(); 
      String getQuery = "SELECT * FROM " + ContactDb.TABLE_NAME; 
      Cursor cursor = db.rawQuery(getQuery, null); 
      Log.e("DbHelper", "while üstünde"); 
      while (cursor.moveToNext()) { 
       //System.out.print("while içinde cursor"); 
       Log.e("DbHelper", "while içinde"); 
       Contact contact = new Contact(); 
       contact.setContactId(cursor.getInt(0)); 
       Log.v("ContactId", "" + cursor.getInt(0)); 
       contact.setContactName(cursor.getString(1)); 
       contact.setContactSurname(cursor.getString(2)); 
       contact.setPhone(cursor.getString(3)); 
       contact.setEmail(cursor.getString(4)); 
       contacts.add(contact); 

       Collections.sort(contacts, new Comparator<Contact>() { 
        @Override 
        public int compare(Contact lhs, Contact rhs) { 
         return lhs.getContactName().compareTo(rhs.getContactName()); 
        } 
       }); 
      } 
      return contacts; 
     } 
public String insertContactToSQLite(Contact contact) { 
     try { 
      SQLiteDatabase db = this.getWritableDatabase(); 
      ContentValues values = new ContentValues(); 
      values.put(ContactDb.COL_CONTACTNAME, contact.getContactName()); 
      values.put(ContactDb.COL_CONTACTSURNAME, contact.getContactSurname()); 
      values.put(ContactDb.COL_CONTACTPHONE, contact.getPhone()); 
      values.put(ContactDb.COL_CONTACTEMAIL, contact.getEmail()); 

      db.insert(ContactDb.TABLE_NAME, null, values); 
      db.close(); 
      Log.e("insertIcınde", "insert basarılı"); 
      return "İşlem başarılı"; 
     } catch (SQLiteAbortException e) { 
      e.printStackTrace(); 
      return "İşlem Başarısız"; 
     } 

    } 

下に表示されDbHelperクラスを持っています例外。私のフラグメントクラスは以下の通りです

public class AddContactFragment extends Fragment { 

public Contact c1 = new Contact(); 
public Contact c2 = new Contact(); 
EditText etName, etSurname, etPhone, etEmail; 
DbHelper dbHelper; 
Button button; 

public AddContactFragment() { 
    // Required empty public constructor 
} 


@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View view = inflater.inflate(R.layout.fragment_add_contact, 
      container, false); 
    button = (Button) view.findViewById(R.id.add_button); 
    etName = (EditText) view.findViewById(R.id.editTextName); 
    etSurname = (EditText) view.findViewById(R.id.editTextSurname); 
    etPhone = (EditText) view.findViewById(R.id.editTextPhone); 
    etEmail = (EditText) view.findViewById(R.id.editTextEMail); 
    // dbHelper =new DbHelper(this.getContext()); 
    button.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 

      try { 

       int a = dbHelper.getAllContacts().size(); 
       Log.e("ContactSize", "" + a); 
      } catch (NullPointerException e) { 
       e.printStackTrace(); 
      } 
      try { 
       if (dbHelper.getAllContacts() == null || dbHelper.getAllContacts().size() <= 5) { 
        // dbHelper.addContactToLocalDb(etName.getText().toString(),etSurname.getText().toString(),etPhone.getText().toString(),etEmail.getText().toString()); 


        etName.getText().toString()); 
        c1.setContactName(etName.getText().toString()); 
        c1.setContactSurname(etSurname.getText().toString()); 
        c1.setPhone(etPhone.getText().toString()); 
        Log.e("kullanıcıId", "" + getUserServerId()); 
        c1.setUserId(getUserServerId()); 

        Log.e("AddContactFragment", "icinde"); 
        c2.setContactName(etName.getText().toString()); 
        c2.setContactSurname(etSurname.getText().toString()); 
        c2.setPhone(etPhone.getText().toString()); 
        c2.setEmail(etEmail.getText().toString()); 

        dbHelper.insertContactToSQLite(c2); 
        try { 
         new MyClient().PostContact(c1); 

         Contact c = dbHelper.getAllContacts().get(0); 
         Log.e("isim", c.getContactName()); 
         Log.e("AddContactFragmentPost", "postEdildi"); 
         Intent newIntent = new Intent(getActivity().getApplicationContext(), NavigationActivity.class); 
         startActivity(newIntent); 
        } catch (JSONException e) { 
         Toast.makeText(getActivity().getApplicationContext(), "You can not add contact more than 5", Toast.LENGTH_SHORT).show(); 
        } 
       } else { 
        Toast.makeText(getActivity().getApplicationContext(), "You can not add contact more than 5", Toast.LENGTH_SHORT).show(); 
       } 
      } catch (NullPointerException e) { 
       e.printStackTrace(); 
      } 
     } 
    }); 


    return view; 
} 

私は助けていただきありがとうございます。

Answer 1

dbHelperインスタンスが初期化されていないため、nullです。それを使用する前に、dbHelper = new DbHelper(getActivity())