Important Namespaces

System Namespace types are as follows.

AppDomain

Represents an application domain, which is an isolated environment where applications execute. This class cannot be inherited.

BitConverter

Converts base data types to an array of bytes, and an array of bytes to base data types.

Environment

Provides information about, and means to manipulate, the current environment and platform. This class cannot be inherited.

Lazy<T>

Provides support for lazy initialization.

Math

Provides constants and static methods for trigonometric, logarithmic, and other common mathematical functions.

OperatingSystem

Represents information about an operating system, such as the version and platform identifier. This class cannot be inherited.

Random

Represents a pseudo-random number generator, which is an algorithm that produces a sequence of numbers that meet certain statistical requirements for randomness.

Uri

Provides an object representation of a uniform resource identifier (URI) and easy access to the parts of the URI.

UriBuilder

Provides a custom constructor for uniform resource identifiers (URIs) and modifies URIs for the Uri class.

DateTime

Represents an instant in time, typically expressed as a date and time of day.

ICloneable

Supports cloning, which creates a new instance of a class with the same value as an existing instance.

IComparable

Defines a generalized type-specific comparison method that a value type or class implements to order or sort its instances.

IComparable<T>

Defines a generalized comparison method that a value type or class implements to create a type-specific comparison method for ordering or sorting its instances.

IDisposable

Provides a mechanism for releasing unmanaged resources.

IEquatable<T>

Defines a generalized method that a value type or class implements to create a type-specific method for determining equality of instances.

Microsoft.Extensions.FileProviders

3 Interfaces

1. IDirectoryContents. Represents a directory's content in the file provider.
2. IFileInfo. Represents a file in the given file provider.
3. IFileProvider. A read-only file provider abstraction.

File Providers in ASP.NET Core- ASP.NET Core abstracts file system access through the use of File Providers. File Providers are used throughout the ASP.NET Core framework. For example:

• IWebHostEnvironment exposes the app's content root and web root as IFileProvider types.
• Static File Middleware uses File Providers to locate static files.
• Razor uses File Providers to locate pages and views.
• .NET Core tooling uses File Providers and glob patterns to specify which files should be published.

IFileProvider Interface

Namespace:

Microsoft.Extensions.FileProviders

Assembly:

Microsoft.Extensions.FileProviders.Abstractions.dll

Package:

Microsoft.Extensions.FileProviders.Abstractions v7.0.0

public interface IFileProvider

Methods

• GetDirectoryContents(String). Enumerate a directory at the given path, if any.
• GetFileInfo(String). Locate a file at the given path.
• Watch(String). Creates a IChangeToken for the specified filter.

Derived classes

• Microsoft.Extensions.FileProviders.CompositeFileProvider
• Microsoft.Extensions.FileProviders.EmbeddedFileProvider
• Microsoft.Extensions.FileProviders.ManifestEmbeddedFileProvider
• Microsoft.Extensions.FileProviders.NullFileProvider
• Microsoft.Extensions.FileProviders.PhysicalFileProvider

Example.

Add the IFileProvider service in ConfigureServices method as shown below.

 public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllersWithViews();
            string root = System.IO.Directory.GetCurrentDirectory();
            IFileProvider fp = new PhysicalFileProvider(root);
            services.AddSingleton(fp);
        }

Add the logic in HomeController/Index action.

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.FileProviders;
using System;
using System.IO;

namespace WebAppMvc1.Controllers
{
    public class HomeController : Controller
    {
        private readonly IFileProvider fileProvider;

        public HomeController(IFileProvider fileProvider)
        {
            this.fileProvider = fileProvider;
        }
        public IActionResult Index()
        {
            var contents = fileProvider.GetDirectoryContents("/");
            foreach (var cnt in contents)
            {
                HttpContext.Response.WriteAsync(cnt.PhysicalPath + Environment.NewLine);
            }
            return View();
        }
    }
}

System.IO Namespace

Contains types( classes, structs, enums and delegates) that allow reading and writing to files and data streams, and types that provide basic file and directory support.

System.IO.Path class

using System;
using System.IO;

namespace ConsoleApp1
{
    internal class Program
    {
        private static void Cw(string s)
        {
            Console.WriteLine(s);
        }
        static void Main(string[] args)
        {
            // path separator character in path string command
            Cw(Path.PathSeparator.ToString());
            Cw(Path.DirectorySeparatorChar.ToString());

            string mypath = @"c:\users\appliedk\abc.pdf";
            Cw(Path.GetDirectoryName(mypath));
            Cw(Path.GetFileName(mypath));
            Cw(Path.GetFileNameWithoutExtension(mypath));
            Cw(Path.GetExtension(mypath));
            Cw(Path.GetFullPath("abc.xyz"));
            Cw(Path.ChangeExtension(mypath,"docx"));
            Cw(Path.EndsInDirectorySeparator(mypath).ToString());
            Cw(Path.GetRandomFileName());
            Cw(Path.GetTempPath());
            Cw(Path.GetTempFileName());
            string[] strings = { "abc", "def", "pqr", "xyz" };
            Cw(Path.Combine(strings));
            Cw(Path.Join(strings));
        }      
    }
}

Microsoft.AspNetCore.Hosting 

Microsoft.AspNetCore.Hosting Namespace provides class and interface types that help configure and start web applications. Important classes and interfaces of this namespace are as follows.

• IWebHost represents a configured web host. To configuring web host, we use methods of IWebHostBuilder. The IWebHost has methods to start or stop the host. It has Services property that returns IServiceProvider; this interface is implemented by a class or value type that provides a service to other objects because it has GetService(Type) method that returns the service object of the specified type.
• IWebHostBuilder is a builder for IWebHost. It has methods to configure app and services and methods to get the setting value from the configuration or replace a setting in the configuration. It has many extension methods available to do different tasks. They are tabulated below.
• IWebHostEnvironment provides information about the web hosting environment an application is running in. It has two properties. 1) WebRootFileProvider that gets or sets an IFileProvider pointing at WebRootPath. This defaults to referencing files from the 'wwwroot' subfolder and WebRootPath that gets or sets the absolute path to the directory that contains the web-servable application content files. This defaults to the 'wwwroot' subfolder.
• EnvironmentName class has fields for commonly used environment names such as Development, Production etc.
• StartupBase: Base class for initializing services and middlewares used by an application. This class has methods like Configure(IApplicationBuilder): Configures the application. ConfigureServices(IServiceCollection): Register services into the IServiceCollection. CreateServiceProvider(IServiceCollection): Creates an IServiceProvider instance for a given ConfigureServices(IServiceCollection).
• WebHostBuilder class: A builder for IWebHost that implements IWebHostBuilder.
• WebHostDefaults class that contains a set of constants representing configuration keys strings.

IWebHostBuilder methods

Build()	Builds an IWebHost which hosts a web application.
ConfigureAppConfiguration(Action<WebHostBuilderContext,IConfigurationBuilder>)	Adds a delegate for configuring the IConfigurationBuilder that will construct an IConfiguration.
ConfigureServices(Action<IServiceCollection>)	Adds a delegate for configuring additional services for the host or web application. This may be called multiple times.
ConfigureServices(Action<WebHostBuilderContext,IServiceCollection>)	Adds a delegate for configuring additional services for the host or web application. This may be called multiple times.
GetSetting(String)	Get the setting value from the configuration.
UseSetting(String, String)	Add or replace a setting in the configuration.

IWebHostBuilder Extension methods

UseAzureAppServices(IWebHostBuilder)	Configures application to use Azure AppServices integration.
CaptureStartupErrors(IWebHostBuilder, Boolean)	Set whether startup errors should be captured in the configuration settings of the web host. When enabled, startup exceptions will be caught and an error page will be returned. If disabled, startup exceptions will be propagated.
PreferHostingUrls(IWebHostBuilder, Boolean)	Indicate whether the host should listen on the URLs configured on the IWebHostBuilder instead of those configured on the IServer.
Start(IWebHostBuilder, String[])	Start the web host and listen on the specified urls.
SuppressStatusMessages(IWebHostBuilder, Boolean)	Specify if startup status messages should be suppressed.
UseConfiguration(IWebHostBuilder, IConfiguration)	Use the given configuration settings on the web host.
UseContentRoot(IWebHostBuilder, String)	Specify the content root directory to be used by the web host.
UseEnvironment(IWebHostBuilder, String)	Specify the environment to be used by the web host.
UseServer(IWebHostBuilder, IServer)	Specify the server to be used by the web host.
UseShutdownTimeout(IWebHostBuilder, TimeSpan)	Specify the amount of time to wait for the web host to shutdown.
UseStartup(IWebHostBuilder, String)	Specify the assembly containing the startup type to be used by the web host.
UseUrls(IWebHostBuilder, String[])	Specify the urls the web host will listen on.
UseWebRoot(IWebHostBuilder, String)	Specify the webroot directory to be used by the web host.
Configure(IWebHostBuilder, Action<IApplicationBuilder>)	Specify the startup method to be used to configure the web application.
Configure(IWebHostBuilder, Action<WebHostBuilderContext,IApplicationBuilder>)	Specify the startup method to be used to configure the web application.
ConfigureAppConfiguration(IWebHostBuilder, Action<IConfigurationBuilder>)	Adds a delegate for configuring the IConfigurationBuilder that will construct an IConfiguration.
ConfigureLogging(IWebHostBuilder, Action<WebHostBuilderContext,ILoggingBuilder>)	Adds a delegate for configuring the provided LoggerFactory. This may be called multiple times.
ConfigureLogging(IWebHostBuilder, Action<ILoggingBuilder>)	Adds a delegate for configuring the provided ILoggingBuilder. This may be called multiple times.
UseDefaultServiceProvider(IWebHostBuilder, Action<WebHostBuilderContext,ServiceProviderOptions>)	Configures the default service provider
UseDefaultServiceProvider(IWebHostBuilder, Action<ServiceProviderOptions>)	Configures the default service provider
UseStartup(IWebHostBuilder, Type)	Specify the startup type to be used by the web host.
UseStartup<TStartup>(IWebHostBuilder)	Specify the startup type to be used by the web host.
UseStartup<TStartup>(IWebHostBuilder, Func<WebHostBuilderContext,TStartup>)	Specify a factory that creates the startup instance to be used by the web host.
UseStaticWebAssets(IWebHostBuilder)	Configures the WebRootFileProvider to use static web assets defined by referenced projects and packages.
UseHttpSys(IWebHostBuilder)	Specify Http.sys as the server to be used by the web host.
UseHttpSys(IWebHostBuilder, Action<HttpSysOptions>)	Specify Http.sys as the server to be used by the web host.
UseIIS(IWebHostBuilder)	Configures the port and base path the server should listen on when running behind AspNetCoreModule. The app will also be configured to capture startup errors.
UseIISIntegration(IWebHostBuilder)	Configures the port and base path the server should listen on when running behind AspNetCoreModule. The app will also be configured to capture startup errors.
ConfigureKestrel(IWebHostBuilder, Action<WebHostBuilderContext,KestrelServerOptions>)	Configures Kestrel options but does not register an IServer. See UseKestrel(IWebHostBuilder).
ConfigureKestrel(IWebHostBuilder, Action<KestrelServerOptions>)	Configures Kestrel options but does not register an IServer. See UseKestrel(IWebHostBuilder).
UseKestrel(IWebHostBuilder)	Specify Kestrel as the server to be used by the web host.
UseKestrel(IWebHostBuilder, Action<WebHostBuilderContext,KestrelServerOptions>)	Specify Kestrel as the server to be used by the web host.
UseKestrel(IWebHostBuilder, Action<KestrelServerOptions>)	Specify Kestrel as the server to be used by the web host.
UseQuic(IWebHostBuilder)	Specify Quic as the transport to be used by Kestrel.
UseQuic(IWebHostBuilder, Action<QuicTransportOptions>)	Specify Quic as the transport to be used by Kestrel.
UseSockets(IWebHostBuilder)	Specify Sockets as the transport to be used by Kestrel.
UseSockets(IWebHostBuilder, Action<SocketTransportOptions>)	Specify Sockets as the transport to be used by Kestrel.
ConfigureTestContainer<TContainer>(IWebHostBuilder, Action<TContainer>)	Configures the IWebHostBuilder instance with the services provided in servicesConfiguration.
ConfigureTestServices(IWebHostBuilder, Action<IServiceCollection>)	Configures the IWebHostBuilder instance with the services provided in servicesConfiguration.
UseSolutionRelativeContentRoot(IWebHostBuilder, String, String)	Sets the content root of relative to the solutionRelativePath.
UseSolutionRelativeContentRoot(IWebHostBuilder, String, String, String)	Sets the content root of relative to the solutionRelativePath.
UseTestServer(IWebHostBuilder)	Enables the TestServer service.
UseTestServer(IWebHostBuilder, Action<TestServerOptions>)	Enables the TestServer service.

System.Environment Class Properties and Methods

using System;

namespace ConsoleApp1
{
    internal class Program
    {
        private static void Cw(string s)
        {
            Console.WriteLine(s);
        }
        static void Main(string[] args)
        {
            Cw(Environment.CommandLine);
            Cw(Environment.MachineName);
            Cw(Environment.CurrentDirectory);
            Cw(Environment.SystemDirectory);
            Cw(Environment.UserName);
            Cw(Environment.OSVersion.VersionString);
            Cw(Environment.SpecialFolder.Desktop.ToString());
            Cw(Environment.GetFolderPath(Environment.SpecialFolder.Desktop));
            Cw(Environment.ProcessId.ToString());
            Cw(Environment.ProcessorCount.ToString());
            Cw(Environment.GetEnvironmentVariable("PATH"));
            Cw(Environment.GetEnvironmentVariables().Count.ToString());
			Cw(Environment.StackTrace);
        }
    }
}

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Updated on 7 July 2023