How to redisplay EditTestPreference when an invalid input was entered?

Question

I am targeting android 2.1.

I have an EditTextPreference that allows users to input some values. If the user inputs an empty value I want to redisplay the edit preference after displaying an error message to the user.

I can display the error message, but I can't redisplay the EditTextPreference again.

My code goes somewhat like this:

public boolean onPreferenceChange(Preference preference, Object newValue) {
    final EditTextPreference editPreference = (EditTextPreference) preference;
    String value = editPreference.getText();
    if (value != null && value.trim() != "") {
        return true;
    } else {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("");
        builder.setMessage("O comando nºao pode ser vazio.");
        builder.setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {

            }
        });
        builder.show();
        return false;
    }
  }