Enumerable.First（System.Linq）C＃的替代方法

Question

I have this piece of code running in .net 3.5

public const string SvgNamespace = "http://www.w3.org/2000/svg";
public const string XLinkPrefix = "xlink";
public const string XLinkNamespace = "http://www.w3.org/1999/xlink";
public const string XmlNamespace = "http://www.w3.org/XML/1998/namespace";

public static readonly List<KeyValuePair<string, string>> Namespaces = new List<KeyValuePair<string, string>>()
{
    new KeyValuePair<string, string>("", SvgNamespace),
    new KeyValuePair<string, string>(XLinkPrefix, XLinkNamespace),
    new KeyValuePair<string, string>("xml", XmlNamespace)
};

private bool _inAttrDictionary;
private string _name;
private string _namespace;

public string NamespaceAndName
        {
            get
            {
                if (_namespace == SvgNamespace)
                    return _name;
                return Namespaces.First(x => x.Value == _namespace).Key + ":" + _name;
            }
        }

and I am currently converting it to .net 2.0 (removing System.Linq). How can I maintain the functionality of Enumerable.First Method (IEnumerable, Func) found here within my code?

Full source file

Answer 1

You can probably use a foreach loop like

foreach(var item in Namespaces)
{
  if(item.Value == _namespace)
    return item.Key + ":" + _name;
}

Answer 2

You can create GetFirst method as follows:

    public string NamespaceAndName
    {
        get
        {
            if (_namespace == SvgNamespace)
                return _name;

            return GetFirst(Namespaces, _namespace).Key + ":" + _name;
        }
    }
    private KeyValuePair<string, string> GetFirst(List<KeyValuePair<string,string>> namespaces,string yourNamespaceToMatch)
    {
        for (int i = 0; i < namespaces.Count; i++)
        {
            if (namespaces[i].Value == yourNamespaceToMatch)
                return namespaces[i];
        }
        throw new InvalidOperationException("Sequence contains no matching element");
    }

Answer 3

It's not really an alternative to Enumerable.First , but since you have actually a List<T> variable, you can consider Find method. The signature is compatible with the Enumerable.First , but note that the behavior is compatible with Enumerable.FirstOrDefault , ie in case the element doesn't exist, you'll get NRE instead of the "Sequence contains no matching element".

return Namespaces.Find(x => x.Value == _namespace).Key + ":" + _name;