[android help] How to change Pin Number using sharedpreferences in Android?

I'm having implement android demo for application pin using shared preferences which i enter pin and confirm the pin.The problem is that when I am accessing this values, it is not returning updated values, it gives me NullPointerException.

String strGetPin;

public final String pref_filename = "settings";
String myPassword;
static SharedPreferences shaedPref;
public static String strdataReturned = "";


public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.settings_list);
        activity=this;


    edtxt_EnterPin  =(EditText)findViewById(R.id.edtxt_Pin);
    edtxt_NewPin    =(EditText)findViewById(R.id.edtxt_NewPin);
    edtxt_ConfirmPin=(EditText)findViewById(R.id.edtxt_ConfirmPin);
    shaedPref = getSharedPreferences(pref_filename, 0);
    strdataReturned = shaedPref.getString("user", "");

    if (strdataReturned.equals("")) 
    {
        SharedPreferences.Editor editor = shaedPref.edit();
        editor.putString("user", "1234"); // newData is new pass,passwordKey is key
        editor.commit();
    }




    btnChangePin=(Button)findViewById(R.id.btn_ChangePin);
    btnChangePin.setOnClickListener(new OnClickListener() 
    {

        @Override
        public void onClick(View v) 
        {
            // TODO Auto-generated method stub
            myDialog=new Dialog(Settings_Activity.this);
            myDialog.setContentView(R.layout.pin_change);
            myDialog.setTitle("Application PIN Change");
            myDialog.setCancelable(false);





            //Button For Change Pin save
            Button btnChange=(Button) myDialog.findViewById(R.id.btn_Save);
            btnChange.setOnClickListener(new OnClickListener() {

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


                    String stringData = edtxt_EnterPin.getText().toString().trim();
                    strdataReturned = shaedPref.getString("user", ""); // key/def message

                    // if stored password is equal to entered password
                    if (strdataReturned.equals(stringData)) 

                    {
                        String newData = edtxt_NewPin.getText().toString().trim();
                        SharedPreferences.Editor editor = shaedPref.edit();
                        editor.putString("user", newData); // newData is new pass, passwordKey is key
                        editor.commit();


                        Toast.makeText(getApplicationContext(),"PIN Change successfully", Toast.LENGTH_LONG).show();
                        edtxt_EnterPin.setText("");
                        edtxt_NewPin.setText("");
                    } 

                    else

                    {
                        Toast.makeText(getApplicationContext(), "Wrong Pin!",Toast.LENGTH_LONG).show();
                        edtxt_EnterPin.setText("");
                        edtxt_NewPin.setText("");
                    }




                }
            });



            Button btnCancel=(Button) myDialog.findViewById(R.id.btn_Cancel);
            btnCancel.setOnClickListener(new OnClickListener() {

                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    myDialog.dismiss();
                }
            });

            myDialog.show();



        }
    });

}

.

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