问无法识别widget？

EN

public class yourActivity extends Activity {
    public final static int DIALOG_ERROR = 1;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        showDialog(DIALOG_ERROR); //this will call: onCreateDialog()
    }

    protected Dialog onCreateDialog(int id) {
        Dialog dialog;
    switch(id) {
    case DIALOG_ERROR:
        //create dialog
        dialog = new AlertDialog.Builder(this).setMessage("Messaging").create();
        break;
    default:
        //create a default dialog
        dialog = null;
    }
    return dialog;
    }

}