C# [LINQ] Linq Expression 获取多格式文件

using System;
using System.IO;
using System.Linq;
using System.Linq.Expressions;

        internal static string[] EnumerateMultiExtensionFiles(string directory, string searchPattern, SearchOption searchOption)
        {
            IQueryable<string> queayableFiles = Directory.GetFiles(directory, "*.*", searchOption).AsQueryable<string>();
            string[] exts = searchPattern.Split(new char[] { '|' }, StringSplitOptions.RemoveEmptyEntries);
            ParameterExpression pe = Expression.Parameter(typeof(string), "ext");
            Expression e = null;

            for (int i = ; i < exts.Length; i++)
            {
                Expression callMethod1 = Expression.Call(pe, typeof(string).GetMethod("ToLower", Type.EmptyTypes));
                Expression callMethod2 = Expression.Constant(exts[i]);
                if (i > )
                {
                    e = Expression.OrElse(e, Expression.Call(callMethod1, typeof(string).GetMethod("EndsWith", new Type[] { typeof(string) }), callMethod2));
                }
                else
                {
                    e = Expression.Call(callMethod1, typeof(string).GetMethod("EndsWith", new Type[] { typeof(string) }), callMethod2);
                }
            }
            MethodCallExpression whereCallExpression = Expression.Call(
                                                        typeof(Queryable),
                                                        "Where",
                                                        new Type[] { queayableFiles.ElementType },
                                                        queayableFiles.Expression,
                                                        Expression.Lambda<Func<string, bool>>(e, new ParameterExpression[] { pe })
                                                        );
            IQueryable<string> result = queayableFiles.Provider.CreateQuery<string>(whereCallExpression);
            return result.ToArray();
        }

调用：
    EnumerateMultiExtensionFiles("x:\\", ".mp3|.flac|.wav", SearchOption.TopDirectoryOnly);