Le thread UI sous Android

Salut
Voici un exemple d'utilisation de thread UI:

public void onClick(View v)
{
String username = usernameEdit.getText().toString();
String password = passwordEdit.getText().toString();
try {
this.authToken = login(username,password);
} catch (IOException ex) {
Log.w("LOGIN","Login network error !",ex);
Toast.makeToast(this,R.string.networkError,Toast.TOAST_LONG).show();
} catch (AuthenticationException ex) {
Log.i("LOGIN","Login failure !",ex);
Toast.makeToast(this,R.string.invalidAuthentication,Toast.TOAST_LONG).show();
}
}