Variable not set after returning from browser activity in Android

Question

I am setting a member variable in a button click listener which also starts a browser activity. My problem is that the variable is null after the browser is closed and the user returns to my application. I am also saving the variable in onSaveInstanceState and restoring it on onRestoreInstanceState, so I don't think memory management is the issue.

If I don't open the browser the variable is set. Could somebody explain to me why this is the case and the common way to fix this issue? Thanks in advance.

// member variable declaration
private String uniqueTokenRequestID;


// in onCreate()
button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            uniqueTokenRequestID = UUID.randomUUID().toString();

            Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
            startActivity(browserIntent);
        }
});

Complete code:

public class LoginActivity extends AppCompatActivity {

    private String uniqueTokenRequestID;
    private Button loginButton;

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

        if (savedInstanceState == null) {
            Network.init(this);
        }

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        toolbar.setTitle("Login");

        setSupportActionBar(toolbar);

        loginButton = (Button) findViewById(R.id.button_login);
        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                uniqueTokenRequestID = UUID.randomUUID().toString();

                Intent browserIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://google.com"));
                startActivity(browserIntent);
            }
        });
    }


    @Override
    protected void onRestoreInstanceState(Bundle savedInstanceState) {
        uniqueTokenRequestID = savedInstanceState.getString("uniqueTokenRequestID");
        super.onRestoreInstanceState(savedInstanceState);
    }


@Override
protected void onSaveInstanceState(Bundle outState) {
    outState.putString("uniqueTokenRequestID", uniqueTokenRequestID);
    super.onSaveInstanceState(outState);
}

@Override
protected void onResume() {
    super.onResume();

    Intent intent = getIntent();
    Uri uri = intent.getData();

    if (uri != null) {
        Log.d("LOGIN", uri.toString());
        String state = uri.getQueryParameter("state");
        String code = uri.getQueryParameter("code");
        String error = uri.getQueryParameter("error");

        if (error != null) {
            Log.e("LOGIN", error);
        }
        else if (state != null && code != null) {
            if (state.equals(uniqueTokenRequestID)) {
                Log.d("API", "Retrieving tokens");

                // successfully logged in
                Reddit.retrieveAccessToken(code, new Reddit.AccessTokenListener() {
                    @Override
                    public void onAccessTokenRetrieved(Account account) {
                        Log.d("API", account.getAccessToken() + " " + account.getRefreshToken() + " " + account.getAccessTokenExpiresIn());
                    }

                    @Override
                    public void onError(String error) {
                        Log.e("API", error);
                    }
                });
            }
        }
    }
}

}