Android : Passing value from one activity to another doesn't work

I tried looking on other questions but nothing seems to work. Trying to pass the value stored in sUsername from activity Username.java to MainActivity.java (username).

This is Username.java:

public class Username extends ActionBarActivity implements View.OnClickListener {
EditText eUsername;
Button login;
String sUsername;



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

    eUsername = (EditText) findViewById (R.id.username);
    sUsername = eUsername.getText().toString();
    login = (Button)findViewById(R.id.login);
    login.setOnClickListener(this); 
}
private void loginClick() {
    Intent intent = new Intent(this, MainActivity.class );
    intent.putExtra("containsUsername", sUsername); //first argument is the name of the string being passed 
    startActivity(intent);
}

public void onClick (View v) {
    switch (v.getId()) {
        case R.id.login:
            loginClick();
            break;
    }
}

and this is MainActivity.java

public class MainActivity extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    Intent intent = getIntent();
    Bundle bundle = intent.getExtras();
    String username = bundle.getString("containsUsername");
    WebView listOfSongs = (WebView) findViewById (R.id.webview);


    String url = "http://ws.audioscrobbler.com/2.0/?method=user.gettoptracks&user="+username+"&api_key=68f82cd7b37e7b23800c2025066531c9&format=json";
    listOfSongs.loadUrl(url); 

}