urldecode解码方法

输入为带有urldecode转码文本，输出正常文本。

//20130625 by zhangyl 
private string ConvertToString(string input) 
        { 
            input = input.Replace("\"", """); 
            input = input.Replace("\/", "/"); 
            string result; 
            if (!input.Contains("\u")) 
            { 
                result = input; 
            } 
            else 
            { 
                StringBuilder stringBuilder = new StringBuilder(); 
                if (input.IndexOf("\u") > 0) 
                { 
                    stringBuilder.Append(input.Substring(0, input.IndexOf("\u"))); 
                    input = input.Substring(input.IndexOf("\u")); 
                } 
                if (!string.IsNullOrEmpty(input)) 
                { 
                    string[] array = input.Split(new string[] 
                    { 
                        "\u" 
                    }, StringSplitOptions.RemoveEmptyEntries); 
                    string[] array2 = array; 
                    for (int i = 0; i < array2.Length; i++) 
                    { 
                        string text = array2[i]; 
                        if (text.Length > 4) 
                        { 
                            string arg = text.Substring(4); 
                            stringBuilder.Append((char)int.Parse(text.Substring(0, 4), NumberStyles.HexNumber) + arg); 
                        } 
                        else 
                        { 
                            if (text.Length == 4) 
                            { 
                                stringBuilder.Append((char)int.Parse(text, NumberStyles.HexNumber)); 
                            } 
                            else 
                            { 
                                if (text.Length < 4 && text.Length > 0) 
                                { 
                                    stringBuilder.Append(text); 
                                } 
                            } 
                        } 
                    } 
                } 
                result = stringBuilder.ToString(); 
            } 
            return result; 
        }