如何使用SQLite从Android中的一个表中获取单个表到另一个表？

Question

我必须创建登录demo的SQLite应用程序。我已完成登录注册，并将数据插入数据库。现在我想插入数据表单注册登录或创建登录页面。当我运行我的应用程序时，我登录时，我得到nullPointerException。

以下是我的数据库适配器代码：

public String getSinlgeEntry(String userName)
    {
        Cursor cursor=db.query("REGISTER", null, " USERNAME=?", new String[]{userName}, null, null, null);
        if(cursor.getCount()<1) // UserName Not Exist
        {
            cursor.close();
            return "NOT EXIST";
        }
        cursor.moveToFirst();
        String password= cursor.getString(cursor.getColumnIndex("PIN"));
        cursor.close();
        return password;                
    }

这是我的登录活动，我必须使用数据库适配器方法，如getSingleEntry

public class Application_Pin_Activity1 extends Activity
{
    Button btnNewRegister;
    Button btnLogin;
    EditText editText_Email , editText_App_Pin;
    String str_EmailId , str_AppPin;

    LeadMgmt_DBAdapter leadMgmt_DataBaseAdapter;


    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.application_pin_activity1);

        leadMgmt_DataBaseAdapter = new LeadMgmt_DBAdapter(this);
        leadMgmt_DataBaseAdapter = leadMgmt_DataBaseAdapter.open();



        editText_Email=(EditText)findViewById(R.id.edittext_enterEmail);
        editText_App_Pin=(EditText)findViewById(R.id.editText_EnterPin);

        btnLogin=(Button) findViewById(R.id.btn_Login);
        btnLogin.setOnClickListener(new OnClickListener() {

            @SuppressWarnings("unused")
            public void onClick(View arg0) {
                // TODO Auto-generated method stub

                str_EmailId=editText_Email.getText().toString().trim();
                str_AppPin=editText_App_Pin.getText().toString().trim();

                // fetch the Password form database for respective user name
                String storedApplication = leadMgmt_DataBaseAdapter.getSinlgeEntry(str_AppPin);

                if(str_AppPin.equals(storedApplication))
                {
                    Toast.makeText(Application_Pin_Activity1.this,"Access Allow", Toast.LENGTH_LONG).show();
                }

                else
                {
                    Toast.makeText(Application_Pin_Activity1.this, "Sorry ! Wron Pin", Toast.LENGTH_LONG).show();
                }


            }
        });


    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // Close The Database
        leadMgmt_DataBaseAdapter.close();
    }
}