【.Net ｜minimal hosting model 】Program.cs 里面的不同写法

本文介绍.net6.0中引入的minimal hosting model和如何将.net6.0以前的版本转换成6.0

1. minimal hosting model长啥样

在入门.net的过程中，我发现program.cs里面的写法有些是长这样的：

var builder = WebApplication.CreateBuilder(args);

builder.Configuration.AddIniFile("appsettings.ini");

var app = builder.Build();

有些是长这样的

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

后者看起来更正式一点，所以我以为第一种是闹着玩的，真正的项目是不会这么用的，但是当我仔细看官方文档的时候发现，其实是不同版本的aps.net的写法，第一种是net6.0的，第二种是.net5.0的。

2. 为何引入minimal hosting model

这个结果真是出乎我意料，所以我就去查了一下为啥要改成闹着玩的方式（其实这种方式由自己的名字：minimal hosting model），然后官方的回答是：简单
对比一下可以发现确实简单了很多，以下是两个等同的配置，在.net5.0的时候是：

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}

和

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddRazorPages();
    }

    // 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();
        }
        else
        {
            app.UseExceptionHandler("/Error");
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        app.UseStaticFiles();

        app.UseRouting();

        app.UseAuthorization();

        app.MapRazorPages();
    }
}

很长，但是有用的就那么几句，再来看看.net6.0的：

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddRazorPages();

var app = builder.Build();

if (!app.Environment.IsDevelopment())
{
    app.UseExceptionHandler("/Error");
    // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
    app.UseHsts();
}

app.UseHttpsRedirection();
app.UseStaticFiles();

app.UseRouting();

app.UseAuthorization();

app.MapRazorPages();

app.Run();

刚好把有用的几句摘抄出来了，所以新的版本确实更简单了

3.如何转换成minimal hosting model

重要的就两个：
IServiceCollection
另一个是IApplicationBuilder 和IWebHostEnvironment
转成6.0就是
builder.Services
和app和app.Environment

参考
https://gist.github.com/davidfowl/0e0372c3c1d895c3ce195ba983b1e03d#custom-dependency-injection-container