C#/.NET编程

dotnet new sln --name Yibi
dotnet new classlib --framework netstandard2.0 --name Yibi.Core
dotnet build src/Yibi.Core/Yibi.Core.csproj

Implementing the Singleton Pattern in C#

导读：c#实现单例的6种模式

Introducting Lazy Evaluation And Fair Scheduling In C#

导读：欣赏代码。

Async OOP 2: Constructors

导读：async/await在构造函数中使用。

Getting Started with NPOI

导读：NPOI系列教程

PDF File Writer C# Class Library

技术点：PDF/C# .NET class library

Converting PDF to Text in C#

导读：There are several main methods for extracting text from PDF files in .NET:
Microsoft IFilter interface and Adobe IFilter implementation.
iTextSharp
PDFBox
PDFlib（https://www.codeproject.com/Articles/4690/Text2PDF）

MarkDig

c# converter; convert .md to html

ConcurrentBag、BlockingCollection相关参考：
[C#/.NET Little Wonders: ConcurrentBag and BlockingCollection](http://geekswithblogs.net/BlackRabbitCoder/archive/2011/03/03/c.net-little-wonders-concurrentbag-and-blockingcollection.aspx)

List<T> is a collection designed to use in single thread applications.

ConcurrentBag<T> is a subtype of ConcurrentCollection<T> designed to simplify using collections in multi-thread environments. If you use ConcurrentCollection you will not have to lock your collection to prevent corruption by other threads. You can insert or take data from your collection with no need to write special locking codes.

BlockingCollection<T> is designed to get rid of the requirement of checking if new data is available in shared collection between threads. if there is new data inserted to shared collection than your consumer thread will awake immediatily. So you do not have to check if new data is available for consumer thread in certain time intervals typically in a while loop.

Asp.Net Core Mvc

//add a action filter
services.AddMvc(opts=> {
    opts.Filters.Add(typeof(ModelStateFeatureFilter));
})

c#

ValueTuple：返回您的特定参数
声明一个decimal并赋值：var price = 0.00m;
转2、8、10、16进制等字符串：Convert.ToString(c, toBase: 16);
自动打开文件：Process.Start(filename);

System.Threading.Timer和System.Timers.Timer执行异步方法：

//System.Threading.Timer
var timer = new System.Threading.Timer(async (e) =>
{
    await RunAsync();

}, null, TimeSpan.Zero,TimeSpan.FromSeconds(5));

//System.Timers.Timer
var _timer2 = new System.Timers.Timer(3000)
{
    AutoReset = true
};
_timer2.Elapsed += new ElapsedEventHandler(OnTimedEvent);
_timer2.Start();

private async Task RunAsync()
{
    await Task.Delay(1000);

    //do...
}

private async void OnTimedEvent(Object source, ElapsedEventArgs e)
{
    //do...
    Console.WriteLine(DateTime.Now.ToString("HH:mm:ss"));
}

多线程代码片段：

var t1 = new Thread(() =>
{
    RunTimer();
});
t1.Start();

var t6 = new Thread(new ThreadStart(RunTimer6));
t6.Start();

异步代码中使用同步：
private readonly SemaphoreSlim _updateLock = new SemaphoreSlim(1, 1);
try{
    await _updateLock.WaitAsync();
}
finally
{
    _updateLock.Release();
}

DateTime Local to DateTime Utc 时间戳：

private long ToUnixDateTime(DateTime dateTime)
{
    if(dateTime.Kind != DateTimeKind.Utc)
    {
        dateTime = dateTime.ToUniversalTime();
    }
    return (long)(dateTime.Subtract(new DateTime(1970, 1, 1))).TotalMilliseconds;
}

使用枚举：

根据当前值获取枚举项：
Enum.TryParse(strStatus, true, out EnumStatus status);
(PasswordFormatOptions)entity.PasswordFormat

get enum description:

public static string ToDescription<TEnum>(this TEnum EnumValue) where TEnum : struct
{
    return GetEnumDescription((Enum)(object)((TEnum)EnumValue));
}

public static string GetEnumDescription(Enum value)
{
    var fi = value.GetType().GetField(value.ToString());

    var attributes = fi.GetCustomAttributes(typeof(DescriptionAttribute), false) as DescriptionAttribute[];

    if (attributes != null && attributes.Any())
    {
        return attributes.First().Description;
    }

    return value.ToString();
}

use like:  
var descr = MyEnum.ToDescription();

密码生成器代码片段：

GenerateHelper.cs：

public class GenerateHelper
{
    private const string _sourceDefault = "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private const string _sourceStrong = "`~!@#$%^&*()-_=+[]{}\\|;:'\",<.>/?";
    private static List<char> _sourceDefaultDatas => _sourceDefault.ToCharArray().ToList();
    private static List<char> _sourceStrongDatas => (_sourceDefault+_sourceStrong).ToCharArray().ToList();

    public static string CreateGenerateCode(PasswordType passwordType)
    {
        List<char> datas = null;
        int n = 0;

        switch (passwordType)
        {
            case PasswordType.Default:
                datas = _sourceDefaultDatas;
                n = 20;
                break;
            case PasswordType.Stronger:
                datas = _sourceStrongDatas;
                n = 30;
                break;
            default:
                throw new ArgumentException("不支持的密码类型", nameof(passwordType));
        }

        return string.Join("", CreateRandomCodes(datas,n));
    }

    private static IEnumerable<char> CreateRandomCodes(List<char> datas, int n)
    {
        byte[] bytes = new byte[n];
        using (var rng = RandomNumberGenerator.Create())
        {
            rng.GetBytes(bytes);
        }

        var itemLength = datas.Count;

        foreach (var item in bytes)
        {
            var index = item % itemLength;

            yield return datas[index];
        }
    }
}


EnumPasswordType.cs：

public enum PasswordType
{
    Default,
    Stronger
}

获取应用程序目录：

string path = "";

//获取和设置当前目录（即该进程从中启动的目录）的完全限定路径。 结果:E:\项目\Test
path = Environment.CurrentDirectory;

// 获取程序的基目录。结果：E:\项目\Test\
path = System.AppDomain.CurrentDomain.BaseDirectory;

// 获取和设置当前目录(该进程从中启动的目录)的完全限定目录。 结果：E:\项目\Test
path = System.Environment.CurrentDirectory ;

// 获取应用程序的当前工作目录，注意工作目录是可以改变的，而不限定在程序所在目录。 结果：E:\项目\Test
path = System.IO.Directory.GetCurrentDirectory();

// 获取和设置包括该应用程序的目录的名称。 结果：E:\项目\Test\
path = System.AppDomain.CurrentDomain.SetupInformation.ApplicationBase;

//获取项目下的Log文件路径 结果：E:\项目\Test\Log
path = System.Web.HttpContext.Current.Server.MapPath("~/Log");