.NET Core第5天_IWebHostEnvironment 的用途是捨麼?

2021 iThome 鐵人賽

DAY 5

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.NET Core MVC網頁應用開發系列第 5 篇

13th鐵人賽

Samuel

2021-09-05 16:55:51

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IWebHostEnvironment用於在runtime期間判斷目前在捨麼環境執行

預設產生的Startup.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace MyCore0
{
    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {

        }
        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapGet("/", async context =>
                {
                    await context.Response.WriteAsync("Hello World!");
                });
            });
        }

    }
}

於Configure傳入的參數可以看到
IWebHostEnvironment的蹤影(.net core 第2版的IHostingEnviroment 為其前身)
3.1後IWebHostEnvironment則變去Implement IHostingEnviroment

主要能提供目前正在執行的Web hosting Environment資訊
使用時要引入Microsoft.AspNetCore.Hosting 這個Namespace

此介面的定義:

public interface IWebHostEnvironment : Microsoft.Extensions.Hosting.IHostEnvironment

https://docs.microsoft.com/en-us/dotnet/api/microsoft.aspnetcore.hosting.iwebhostenvironment?view=aspnetcore-3.1

在ASP.NET Core3.1 Default將環境分為三種：
IsDevelopment：開發環境
Checks if the current hosting environment name is Development.
預設模式，為在開發應用時期用的環境

IsStaging：暫時測試(預演)環境
Checks if the current hosting environment name is Staging.
部屬到正式生產環境中最後測試的環境

IsProduction：正式環境
Checks if the current hosting environment name is Production.

額外的第四種則是確認某一指定值是否就是目前的執行環境名
IsEnvironment :
True if the specified name is the same as the current environment, otherwise false.
Compares the current hosting environment name against the specified value.
會忽略大小寫!!

而要有這些環境擴充屬性需要有Microsoft.Extensions.Hosting此參考
上述這些Extension methods被定義於
Microsoft.AspNetCore.Hosting命名空間下的HostingEnvironmentExtensions Class中

當中定義兩屬性

1.WebRootPath − Path of the www folder(Gets or sets the absolute path to the directory that contains the web-servable application content files)

2.ContentRootPath − Path of the root folder which contains all the Application files(Gets or sets an IFileProvider pointing at WebRootPath.)

實際輸出觀察
Test Code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

namespace MyCore0
{
    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {

        }
        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            app.Use(async (context, next) =>
            {
                await context.Response.WriteAsync("1st Middleware in. \r\n");
                await context.Response.WriteAsync(String.Format("Is Development Env:{0} \r\n", env.IsDevelopment()));
                await context.Response.WriteAsync(String.Format("Is Staging Env:{0} \r\n", env.IsStaging()));
                await context.Response.WriteAsync(String.Format("Is Production Env:{0} \r\n", env.IsProduction()));
                await context.Response.WriteAsync(String.Format("Environment Name:{0} \r\n", env.EnvironmentName));
                await context.Response.WriteAsync(String.Format("Is Match Current Environment Name:{0} \r\n", env.IsEnvironment("Development")));
                await context.Response.WriteAsync(String.Format("Is Match Current Environment Name:{0} \r\n", env.IsEnvironment("Staging")));
                await context.Response.WriteAsync(String.Format("WebRootPath:{0} \r\n", env.WebRootPath));
                await context.Response.WriteAsync(String.Format("ContentRootPath:{0} \r\n", env.ContentRootPath));
                await context.Response.WriteAsync(String.Format("ApplicationName:{0} \r\n", env.ApplicationName));
            });
        }

    }
}