如何将TypeConverters用于日历？

Question

我正在尝试将日历转换为long，以便使用空间添加到数据库中。

我以为我的代码可以用，但是好像失败了。

@Entity(tableName = "reminders")
public class Reminder {

@PrimaryKey(autoGenerate = true)
private int rid;

private String name;
private String note;
@TypeConverters({CalendarConverter.class})
private Calendar calendar;
private int priority;
private boolean enabled;


public Reminder(String name, String note, String date, int priority, int enabled) {


    this.name = name;
    this.note = note;
    this.priority = priority;

    if (enabled == 0)
        this.enabled = false;
    else
        this.enabled = true;

    String[] dateSplit = date.split("/");

    int day = Integer.parseInt(dateSplit[0]);
    int month = Integer.parseInt(dateSplit[1]);
    int year = Integer.parseInt(dateSplit[2]);

    calendar = new GregorianCalendar(year, month - 1, day);

}



public class CalendarConverter {

@TypeConverter
public static GregorianCalendar fromLong(Long value) {
    if (value == null) {
        throw new NullPointerException("must not be null");
    }
    GregorianCalendar cal = new GregorianCalendar();
    cal.setTime(new Date(value));
    return cal;
}

@TypeConverter
public static Long toLong(GregorianCalendar calendar) {
    if (calendar != null) {
        throw new NullPointerException("must not be null");
    }
    Calendar cal = calendar;
    return cal.getTimeInMillis();
}

}

我找不到尝试将日历转换为long时犯的错误。

  

错误：“无法弄清楚如何将该字段保存到数据库中。您可以考虑为其添加类型转换器。”