WPF + C# Extract a Substring from a String between two specified Parts

ExtractSubstring.cs

using System;
using System.Collections.Generic;
using System.Windows;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Windows.Input;
using System.Xml.Linq;

namespace StringProgram
{
    public partial class StringProgram : Window
    {
        // Extracts a substring from 'originalStr', which lies between 'beginStr' and 'endStr'.
        // 'includeBeginAndEnd' specifies whether 'beginStr' and 'endStr' are incldued in the extracted string.
        public static bool GetSubstringByString(string beginStr, string endStr, string originalStr, bool includeBeginAndEnd, out string substring, out string msg)
        {
            bool ret = true;
            substring = string.Empty;
            msg = string.Empty;

            if (!originalStr.Contains(beginStr) || !originalStr.Contains(endStr))
            {
                msg = ERR_STR_DOES_NOT_CONTAIN;
                ret = false;
            }
            else
            {
                if (originalStr.IndexOf(beginStr) >= originalStr.IndexOf(endStr))
                {
                    msg = ERR_STR_END_BEFORE_BEGIN;
                    ret = false;
                }
                else
                {
                    int beginIndex = 0;
                    int len = 0;
                    if (includeBeginAndEnd)
                    {
                        beginIndex = originalStr.IndexOf(beginStr);
                        len = originalStr.IndexOf(endStr) - originalStr.IndexOf(beginStr) + endStr.Length;
                    }
                    else
                    {
                        beginIndex = originalStr.IndexOf(beginStr) + beginStr.Length;
                        len = originalStr.IndexOf(endStr) - originalStr.IndexOf(beginStr) - beginStr.Length;
                    }

                    substring = originalStr.Substring(beginIndex, len);
                }
            }

            return ret;
        }
    }
}

Based on an answer here:

http://stackoverflow.com/a/4822334/302248