C# LINQ to XML：来自 XElement 的“安全”枚举值？

Question

To get a "safe" integer value from an XElement in C# one can use a method like

    public int GetIntegerValue(XElement x, string tag)
    {
        int result  = Int32.MinValue;
        if (x.Element(tag) != null)
        {
            Int32.TryParse(x.Element(tag).Value, out result);
        }
        return result;
    }

The code returns the correct integer value if the element is present and contains a parseable string, otherwise Int32.MinValue. This approach would function with a few other common types like double, bool, etc., but what about enum?

Can there also be a function like GetEnumValue(XElement x, string tag, Type enumType) or GetEnumValue(XElement x, string tag, TEnum defaultValue) or alike?

Answer 1

You can try following method:

public static TEnum GetEnumValue<TEnum>(XElement x, string tag)
    where TEnum : struct
{
    // Set default value
    TEnum parsedEnum = default(TEnum);

    var element = x.Element(tag);
    if(element != null)
    {
        // Try to parse
        Enum.TryParse<TEnum>(element.Value, out parsedEnum);
    }

    return parsedEnum;
}

And then call it like:

CarType carType = GetEnumValue<CarType>(xElement, tag);

Answer 2

You can CAST an ENUM to an integer. Also you can use the .ToString() to help Identify the enum types.

Try this code below - it is very quick, but it does work.

using System;
using System.Xml;
using System.Xml.Linq;

public class Program
{
    public enum testTypes { test1, test2, test3};


    private static testTypes GetEnumValue(XElement x, string tag)
    {
        if (x.Element(tag)!=null) {
            var v = x.Element(tag).Value.ToString();
            var testEnums = Enum.GetValues(typeof(testTypes));
            foreach (testTypes enumType in testEnums) {
                if (v.Equals((testTypes) enumType)) return enumType;
            }
        }
        return (testTypes) 0;
    }

    public static void Main()
    {

        XElement x = new XElement("MyType","Test1");
        var EnumVal = GetEnumValue(x, "MyType");    
        Console.WriteLine("Type is {0}",(testTypes) EnumVal);

    }
}

You could actually use Generics to generalise the approach instead of using the static Method.

Answer 3

Working with previous Adil, one can also create an extension function as follow :

public static TEnum ToEnumValue<TEnum>(this XElement xelem)
        where TEnum : struct
    {
        if (xelem is null)
        {
            throw new ArgumentNullException(nameof(xelem));
        }

        Enum.TryParse<TEnum>(xelem.Value, out TEnum parsedEnum);
        return parsedEnum;
    }

then it can be used as follow :

MyViewModel.Mode = node.Element("MyMode")?.ToEnumValue<ModeEnum>() ?? ModeEnum.Mode1;