在 lambda 表达式中使用私有方法

Question

I am working on the logic handle and got this trouble. If I use this code, it's not working:

private bool CheckDateTimeIsValid(DateTime startTime, DateTime endTime, DateTime dateTime)
{
    if (DateTime.Compare(startTime, dateTime) <= 0 && DateTime.Compare(endTime, dateTime) >= 0)
    {
        return true;
    }

    return false;
}

var listChallengeUsers = _context.ChallengeUseres
            .Where(cu => cu.AppUserId == activity.AppUserId)
            .Where(cu => cu.Challenge.ActivityType == activity.Type)
            .Where(cu => CheckDateTimeIsValid(cu.Challenge.StartTime, cu.Challenge.EndTime, activity.CreatedAt))

But if I use this, it worked:

var listChallengeUsers = _context.ChallengeUseres
            .Where(cu => cu.AppUserId == activity.AppUserId)
            .Where(cu => cu.Challenge.ActivityType == activity.Type)
            .Where(cu => DateTime.Compare(cu.Challenge.StartTime, activity.CreatedAt) <= 0 && DateTime.Compare(cu.Challenge.EndTime, activity.CreatedAt) >= 0 )
            .ToList();

Can someone help's me to know why it happen and how to use in the first way?

Answer 1

Your method isn't marked as "static", so either call it via instance or mark the method as static, like this:

private static bool CheckDateTimeIsValid ( DateTime startTime, DateTime endTime, DateTime dateTime )
{
    if (DateTime.Compare ( startTime, dateTime ) <= 0 && DateTime.Compare ( endTime, dateTime ) >= 0)
    {
        return true;
    }

    return false;
}

Also, your code can be shorter like this:

static bool CheckDateTimeIsValid ( DateTime startTime, DateTime endTime, DateTime dateTime ) => startTime <= dateTime && dateTime <= endTime;

And if u decide the method to be static, then it makes more sense to put this method as an extension, if u will use this method often in different places:

public static class DateTimeExts
{
    public static bool CheckDateTimeIsValid ( this DateTime dateTime, DateTime startTime, DateTime endTime ) => startTime <= dateTime && dateTime <= endTime;
}