Updating password in sharedpreferences at android studio

Question

I'm working on an android studio project using sharedpreferences that is a login/register simple application.

I have an activity for changing the password for an existed user and it keeps getting errors and crashes.

Main activity:

public class MainActivity extends AppCompatActivity {
    TextView txtv;
    Button chgpwd;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        txtv = (TextView) findViewById(R.id.txtvSignUp);
        txtv.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Intent i = new Intent(getApplicationContext(),
                        NewUserActivity.class);
                startActivity(i);
                finish();
            }
        });

        chgpwd = (Button) findViewById(R.id.changePwd);
        chgpwd.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                Intent c = new Intent(getApplicationContext(),
                        PasswordUpdateActivity.class);
                startActivity(c);
                finish();
            }
        });

    }
    public void usrLogIn(View v) {
        // To link to the the view objects and read data
        EditText uname = (EditText) findViewById(R.id.nameInp);
        EditText upass = (EditText) findViewById(R.id.pwdInp);
        String username = uname.getText().toString();
        String userpass = upass.getText().toString();
        // To open sharedPref, Create if not exist
        SharedPreferences userAcc = getSharedPreferences("UsersAccounts", 0);
        // To Check if user name exists in the sharedPref.
        if (!userAcc.contains(username)) {
            Toast.makeText(getApplicationContext(), "User NOT Exists",
                    Toast.LENGTH_LONG).show();
            return;
        }
        // To chaeck if the entered password match the password stored in
        // SharedPref object
        if (userAcc.getString(username, null).equals(userpass)) {
            Toast.makeText(getApplicationContext(), "Access Authenticated",
                    Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(getApplicationContext(), "Password is wrong",
                    Toast.LENGTH_LONG).show();
        }
    }

}

New user activity:

public class NewUserActivity extends AppCompatActivity {

    SharedPreferences usrAccs;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_new_user);
    }

    public void signUp(View v) {
        // Read username and password from input fields
        EditText usr = (EditText) findViewById(R.id.usrInp);
        EditText pwd = (EditText) findViewById(R.id.pwdInp);
        // Define SharedPreference object
        usrAccs = getApplicationContext().getSharedPreferences("UsersAccounts", 0);
        // To create editor object for sharedPref
        SharedPreferences.Editor userEdit = usrAccs.edit();
        //To Check if user name already exists
        if (usrAccs.contains(usr.getText().toString())) {
            Toast.makeText(getApplicationContext(), "User already Exists",
                    Toast.LENGTH_LONG).show();
            return;
        }
        // If It pass the if statement, it means the user does not exist
        // and store info in sharedPref using Editor
        userEdit.putString(usr.getText().toString(),pwd.getText().toString());
        userEdit.commit();
        Toast.makeText(getApplicationContext(), usr.getText().toString() + " Account is created", Toast.LENGTH_LONG).show();
                // To return To the main activity
                Intent i = new Intent(getApplicationContext(), MainActivity.class);
        startActivity(i);
        finish();
    }

}

and lastly the password changing activity:

public class PasswordUpdateActivity extends AppCompatActivity {

    SharedPreferences usrAccu;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_password_update);
    }

    public void usrUpdate(View v) {
        // To link to the the view objects and read data
        EditText userr = (EditText) findViewById(R.id.etpwd);
        EditText pwdrr = (EditText) findViewById(R.id.etname);
        Button btnup = (Button) findViewById(R.id.btnChange);

        String newpwd = pwdrr.getText().toString();
        String  updatedPwd = usrAccu.getString("userpass", "");
        usrAccu = PasswordUpdateActivity.this.getSharedPreferences("UsersAccounts", 0);

        //To Check if user name already exists
        if (usrAccu.contains(userr.getText().toString())) {
                SharedPreferences.Editor editor = usrAccu.edit();
                editor.putString("userpass", newpwd);
                editor.commit();

                Toast.makeText(getApplicationContext(), "Password Updated", Toast.LENGTH_LONG).show();
        }
        else{
            Toast.makeText(getApplicationContext(), "User Doesn't Exists", Toast.LENGTH_LONG).show();
        }
    }
}

Answer 1

I think that you first must create your usrAccu.

public void usrUpdate(View v) {
    // To link to the the view objects and read data
    EditText userr = (EditText) findViewById(R.id.etpwd);
    EditText pwdrr = (EditText) findViewById(R.id.etname);
    Button btnup = (Button) findViewById(R.id.btnChange);

    usrAccu = PreferenceManager.getDefaultSharedPreferences(this);

    String newpwd = pwdrr.getText().toString();
    String  updatedPwd = usrAccu.getString("userpass", "");

    //To Check if user name already exists
    ....