string.Join - “cannot convert from IEnumerable to string[]”

问题

Very simple extension method not compiling:

public static string Join(this string text, params string[] stringsToJoin)
{
    return String.Join(", ", stringsToJoin.Where(s => !string.IsNullOrEmpty(s)));
}

I get "cannot convert from 'System.Collections.Generic.IEnumerable' to 'string[]'"

What am I missing?

回答1:

The overload of String.Join which accepts an IEnumerable<String> was only added in .NET 4.0. It seems you're compiling against an earlier version.

The easiest way to fix this and make it compatible with .NET 3.5 would be to simply call .ToArray():

public static string Join(this string text, params string[] stringsToJoin)
{
    return String.Join(", ", stringsToJoin.Where(s => !string.IsNullOrEmpty(s))
                                          .ToArray());
}

来源：https://stackoverflow.com/questions/17871370/string-join-cannot-convert-from-ienumerable-to-string