隨著擼碼的時間增加，碼感也會加強，今天看一個編碼直覺案例吧！

案例：

需求：把查詢到的數據列表生成csv文件

nuget包：CsvHelper

數據實體類：

/// <summary>/// 商品/// </summary>public class Goods{/// <summary>/// 編號/// </summary>public uint ID{ get; set; }/// <summary>/// 名稱/// </summary>public string Name{ get; set; }/// <summary>/// 規格/// </summary>public string Spec{ get; set; }/// <summary>/// 單位/// </summary>public string Unit{ get; set; }/// <summary>/// 制造商/// </summary>public string Manufacturer{ get; set; }/// <summary>/// 價格/// </summary>public decimal Price{ get; set; }/// <summary>///?這里是為了打印數據方例重寫ToString()/// </summary>public override string ToString(){return $"ID={ID},Name={Name},Unit={Unit},Spec={Spec},Price={Price},Manufacturer={Manufacturer}";}}

定義了一個csv操作的接口：

public interface ICsvHandle {List<Goods> ReadCsv(string file);void?WriteCsv(string?file,?List<Goods>?goodses); }

為了演示方便，Demo中的數據列表是通過Bogus產生(bogus在之前的文章中介紹過)

static List<Goods> GoodsCreater(){var goodses = new List<Goods>();var options = new JsonSerializerOptions();options.Encoder = System.Text.Encodings.Web.JavaScriptEncoder.Create(UnicodeRanges.All);for (var i = 0; i < 100; i++){var goodsFaker = new Faker<Goods>("zh_CN").RuleFor(x => x.ID, x => x.Random.UInt()).RuleFor(x => x.Name, x => x.Random.ArrayElement(new string[]{"甲銷唑注射液", "葡萄糖注射液", "鹽水（氯化鈉）", "利巴韋林病毒唑針", "氟康唑氯化鈉注射液(康銳）", "安痛定針", "維生素B12針", "硫酸阿米卡星注射液", "氯化鈉注射液（塑料瓶）", "轉移因子注射液", "血塞通粉針", "苦碟子注射液", "注射用培美曲塞二鈉(愛立汀)", "左克注射液", "維生素C注射液", "硫酸慶大霉素注射液", "鹽酸左氧氟沙星注射液", "蔗糖鐵注射液", "注射用青霉素鈉", "維生素B1針", "疏血通注射液", "胃復安鹽酸甲氧氯普胺注射液", "硫酸慶大霉素注射液", "葡萄糖注射液50%", "銀杏達莫注射液", "硫酸慶大霉素注射液", "5%葡萄糖注射液", "注射用氨曲南",})).RuleFor(x => x.Price, x => x.Random.Decimal()).RuleFor(x => x.Unit, x => x.Random.ArrayElement(new string[] { "個", "片", "瓶", "盒", "支", "克" })).RuleFor(x => x.Spec, x => x.Random.ArrayElement(new string[]{"5*20ml", "250ml", "1ml*10支", "100ml:0.2g", "2毫升*10支", "10支", "2ml*10.2克*10支", "100ml", "3毫升：2毫升*10支", "20毫克", "10mg*10支", "0.5克", "2ml:0.1g", "0.25G*2ML", "4萬單位*10支", "100ml*0.1g", "1g", "80萬單位", "2ml*10支", "5毫克*60片", "1ml:10mg", "4萬*2ml*10支", "20ML*5支", "5ml", "2ml:40mg(4萬單位)", "250ml", "0.5克*10支", "5ML;17.5MG", "2ML:0.5G*10支",})).RuleFor(x => x.Manufacturer, x => x.Random.ArrayElement(new string[]{"山東齊都藥業/山西云鵬", "侯馬霸王藥業/山西晉新雙鶴/天津新鄭/西安/貴州", "山西臨汾云鵬藥業、山東齊都藥業/山西銀湖/石家莊四藥/河南科倫", "安徽聯誼/無錫", "揚子江藥業集團", "新鄉常樂制藥/山西太原藥業/天津焦作/鄭州", "天津藥業焦作", "山東方明藥業集團股份有限公司", "石家莊四藥有限公司", "湖南一格制藥有限公司", "哈爾濱", "通化華夏制藥有限責任公司", "德州德藥制藥有限公司", "揚子江藥業", "山西晉新雙鶴藥業/新鄉市新輝藥業/河南潤弘", "河南輔仁懷慶堂制藥/濮陽市匯元藥業/新鄉常樂", "廣西裕源藥業、四川科倫大藥廠", "成都天臺山制藥有限公司", "華北制藥", "安陽九州藥業、山東方明藥業/石藥銀湖制藥", "牡丹江友博藥業有限公司", "濮陽匯元/天津藥業集團新鄭", "天津藥業焦作/侯馬", "湖南科倫/焦作民康", "貴州益佰制藥股份有限公司", "新鄉市新輝藥業/新鄉常樂制藥/濮陽市匯元藥業", "山東華魯制藥/山東齊都/山西云鵬制藥/西安漢豐", "重慶圣華曦藥業",}));goodses.Add(goodsFaker.Generate());}return goodses;}

第一版：

csv文件格式是utf8

public class BasisCsvHandle : ICsvHandle {public List<Goods> ReadCsv(string file){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var reader = new StreamReader(file))using (var csv = new CsvReader(reader, config)){var goodses = csv.GetRecords<Goods>();return goodses.ToList();}}public void WriteCsv(string file, List<Goods> goodses){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var writer = new StreamWriter(file)){using (var csv = new CsvWriter(writer, config)){csv.WriteRecords(goodses);}}} }

后來有的客戶要BOM類型的UTF8，其實就是在文件開頭加上byte[] BOM = { 0xEF, 0xBB, 0xBF };這個字節數組就ok

為了適配合有無BOM和非BOM的UTF8，對接口進行了重構，增加默認屬性(正好練一下接口默認屬性的用法)，這種做法的好處是不打擾BasisCsvHandle的代碼，當然，也可以更深層的重構ICsvHandle中的兩個方法來適配是否是BOM UTF8

public interface ICsvHandle {List<Goods> ReadCsv(string file);void?WriteCsv(string?file,?List<Goods>?goodses);private static bool _isBOM;public bool IsBOM { get => _isBOM; set => _isBOM = value; } }

第二版：

public class StrengthenCsvHandle : ICsvHandle {public List<Goods> ReadCsv(string file){MemoryStream memory = null;using (var reader = new FileStream(file, FileMode.OpenOrCreate, FileAccess.ReadWrite)){var bytes = new byte[reader.Length];reader.Read(bytes, 0, bytes.Length);if (((ICsvHandle)this).IsBOM){bytes = bytes.Skip(3).Take(bytes.Length - 3).ToArray();}memory = new MemoryStream(bytes);}var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var reader = new StreamReader(memory))using (var csv = new CsvReader(reader, config)){var goodses = csv.GetRecords<Goods>();return goodses.ToList();}}public void WriteCsv(string file, List<Goods> goodses){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var writer = new StreamWriter(file)){using (var csv = new CsvWriter(writer, config)){csv.WriteRecords(goodses);}}if (((ICsvHandle)this).IsBOM){//追究加BOMusing (var writer = new FileStream(file, FileMode.OpenOrCreate, FileAccess.ReadWrite)){var bytes = new byte[writer.Length];writer.Read(bytes, 0, bytes.Length);byte[] BOM = { 0xEF, 0xBB, 0xBF };var list = new List<byte>();list.AddRange(BOM);list.AddRange(bytes);writer.Position = 0;writer.Write(list.ToArray(), 0, list.Count);}}} }

雖然能實現功能，但是覺得這樣的代碼太啰嗦，這里的本質就是在寫數據時加上三個字節，讀取數據時，少讀三個字節，直覺告訴我，應該好像也許或者能有更簡單的方式。

第三版：

public class PerfectCsvHandle : ICsvHandle {public List<Goods> ReadCsv(string file){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var reader = new StreamReader(file))using (var csv = new CsvReader(reader, config)){if (((ICsvHandle)this).IsBOM){reader.BaseStream.Position = 3;}var goodses = csv.GetRecords<Goods>();return goodses.ToList();}}public void WriteCsv(string file, List<Goods> goodses){var config = new CsvConfiguration(CultureInfo.InvariantCulture){NewLine = "\r\n"};using (var writer = new StreamWriter(file)){using (var csv = new CsvWriter(writer, config)){if (((ICsvHandle)this).IsBOM){byte[] BOM = { 0xEF, 0xBB, 0xBF };writer.Write(System.Text.Encoding.UTF8.GetString(BOM));}csv.WriteRecords(goodses);}}} }

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