使用整数设置枚举属性并验证参数

Question

EDIT: I have changed the title of the question to include the validation of the argument, to be clearer what I am asking.

I am attempting to create a class in C# which has a property that is set with an int and returns an enum, this may be really basic but I am a C# noob.

The setting by use of an int argument is a particular limitation that I won't go into and is something that is getting set over COM in Vbscript.

I am looking to create these RSSCalendarDay objects so they can be put in a list and each have a unique RSSCalendarRuleDay from Sunday to Saturday (1 to 7).

Its for part of a really basic approach to using xCal with local data to make recurring events.

My code so far is below and you can see the get & set are incomplete, I am stuck on the validation of the argument (check its an int first, etc), thats what I was previously trying to use dayOrderValue for, and all I could find online in relation was the use of int.Parse and int.TryParse but they were for parsing a string, not for what I want to do.

public class RSSCalendarDay {

    private RSSCalendarRuleDay? _dayOrder;
    /// <summary>
    /// Passed an Integer from 1 to 7 to represent the particular day of the week as an enum
    /// </summary>
    public RSSCalendarRuleDay? DayOrder {
        get {
                       // TODO
        } 
        set {
            if (value != null) {
                int dayOrderValue;
                if () {
                    throw new ArgumentException("Invalid day order specified");
                }
                if(dayOrderValue < 1 || dayOrderValue > 7) {
                    throw new ArgumentException("Invalid day type specified (out of day range of 1 to 7)");
                }
                _dayOrder = (RSSCalendarRuleDay) dayOrderValue;
            }
            else {
                _dayOrder = null;
            }
        } 
    }
    public DateTime? TimeOpens { get; set; }
    public DateTime? TimeCloses { get; set; }

    /// <summary>
    /// These are the relevant BYDAY abbreviations used in the xCal recurring rule specification
    /// to represent what days a recurring event is open in a comma separated list
    /// </summary>
    public enum RSSCalendarRuleDay {
        SU=1,MO=2,TU=3,WE=4,TH=5,FR=6,SA=7
    }
}

Answer 1

You can convert an int to an Enum like so

RSSCalendarRuleDay foo = Enum.ToObject(typeof(RSSCalendarRuleDay) , intValue);

Or by simply casting it

RSSCalendarRuleDay foo = (RSSCalendarRuleDay) intValue;

Do note that since you're using a setter, the setter will expect an Enum value, not an integer, so you will need to cast it before using the setter.

Do note that ToObject will always succeed, even if the value is not defined for the Enum. if you want to do a bounds check, you can use the Enum.IsDefined method

var exists = Enum.IsDefined(typeof(RSSCalendarRuleDay) , intValue);

Answer 2

You cannot define a property that is “set with an int and returns an enum”. By design, the getter and the setter of a property be declared of the same type.

However, what you can do is define two properties which both access the same backing field, one as your enum, and the other cast to an int:

public class RSSCalendarDay
{
    private RSSCalendarRuleDay? dayOrder;

    public RSSCalendarRuleDay? DayOrder
    {
        get { return this.dayOrder; }
        set { this.dayOrder = value; }
    }

    public int DayOrderInt
    {
        get { return this.dayOrder.HasValue ? (int)this.dayOrder: 0; }
        set { this.dayOrder = value != 0 ? (RSSCalendarRuleDay?)value : null; }
    }
}

In the above code, I have simplified your logic to set the backing field to null if you specify an int value of 0 (and vice versa); this may not be what you want.

Consequently, the two following assignments will have identically the same effect:

RSSCalendarDay cd1 = new RSSCalendarDay();
cd1.DayOrder = RSSCalendarRuleDay.TH;

RSSCalendarDay cd2 = new RSSCalendarDay();
cd2.DayOrderInt = 5;

Edit : If you want to perform validation of the argument, you can use a similar approach:

public class RSSCalendarDay
{
    private RSSCalendarRuleDay dayOrder;

    public RSSCalendarRuleDay DayOrder
    {
        get { return this.dayOrder; }
        set { this.dayOrder = value; }
    }

    public int DayOrderInt
    {
        get 
        { 
            return (int)this.dayOrder;
        }
        set
        {
            if (!Enum.IsDefined(typeof(RSSCalendarRuleDay), value))
                throw new ArgumentException("Invalid day value specified (out of day range of 1 to 7).");
            this.dayOrder = (RSSCalendarRuleDay)value; 
        }
    }
}

Enum.IsDefined checks whether the enumeration contains the specified value. In your case, the condition is equivalent to value < 1 || value > 7 value < 1 || value > 7 .

Note that in the above code, DayOrder is not nullable, and 0 is considered an invalid day value.

Edit ₂ : Re the default value issue: My personal preference is to define the 0 ^th member of the enumeration to be unknown; to continue with your two-letter convention, I'm naming it NA (for “not available”).

public enum RSSCalendarRuleDay {
    NA=0,SU=1,MO=2,TU=3,WE=4,TH=5,FR=6,SA=7
}

This is convenient because, when you initialize an RSSCalendarDay instance without explicitly setting its dayOrder field, it would automatically default to RSSCalendarRuleDay.NA . The second snippet I gave above would also work unchanged with this alteration, since Enum.IsDefined would now accept a range of 0–7 (rather than 1–7).

Answer 3

Don't over-complicate your code: enums are represented internally by numbers ( int per default), so it is possible to cast from an int to an enum value (and vice-versa).

So here's how you could simply do:

public RSSCalendarRuleDay DayOrder { get; set; }

...

RSSCalendarDay xx = new RSSCalendarDay(...)
xx.DayOrder = (DayOrder)4;  // Will set WE for the DayOrder property

...

// If you need to get the value as an int
int dayOrderAsInt = (int)xx.DayOrder;

// Still possible to affect invalid values however
RSSCalendarRuleDay z = (RSSCalendarRuleDay)8;

// So if you want to check for int validity:
if (Enum.IsDefined(typeof(RSSCalendarRuleDay), dayOrderAsInt))
{
    // If we're here, the value is valid !
}

Also, make sure you really need DayOrder to be nullable (if it's not the case, remove the ?).

Answer 4

The issue is that you can't receive anything different than an Enum in the setter for your property since you declared it as Enum . One alternative could be something like this:

private int? dayOrderInt;

public int? DayOrderInt
{
     get { return dayOrderInt; }
     set { if (value < 1 || value > 7) throw new ArgumentException(string.Format("{0} is an invalid day of the week", value)); dayOrderInt = value; }
}

public RSSCalendarRuleDay? DayOrder
{
    get { if (DayOrderInt.HasValue) return (RSSCalendarRuleDay)DayOrderInt; return null; }
}

Answer 5

以下对我有用：

RSSCalendarRuleDay Example = (RSSCalendarRuleDay)1; 

Answer 6

I don't think that is achievable. You are setting your property type to RSSCalendarRuleDay? and when you want to pass az integer to it the compiler will throw an error. And by the way this approach is very confusing (like when you intended to return an IEnumerable but sometimes you do return null).