IMiddlewareFactory/IMiddleware 是中間件激活的擴展點。

UseMiddleware 擴展方法檢查中間件的已注冊類型是否實現(xiàn) IMiddleware。?如果是，則使用在容器中注冊的 IMiddlewareFactory 實例來解析 IMiddleware 實現(xiàn)，而不使用基于約定的中間件激活邏輯。?中間件在應(yīng)用的服務(wù)容器中注冊為作用域或瞬態(tài)服務(wù)。

優(yōu)點：

• 按客戶端請求（作用域服務(wù)的注入）激活

• 讓中間件強類型化

IMiddleware 按客戶端請求（連接）激活，因此作用域服務(wù)可以注入到中間件的構(gòu)造函數(shù)中。

IMiddleware

IMiddleware 定義應(yīng)用的請求管道的中間件。InvokeAsync(HttpContext, RequestDelegate)?方法處理請求，并返回代表中間件執(zhí)行的 Task。

使用約定激活的中間件：

public class ConventionalMiddleware {private readonly RequestDelegate _next;public ConventionalMiddleware(RequestDelegate next){_next = next;}public async Task InvokeAsync(HttpContext context, AppDbContext db){var keyValue = context.Request.Query["key"];if (!string.IsNullOrWhiteSpace(keyValue)){db.Add(new Request(){DT = DateTime.UtcNow, MiddlewareActivation = "ConventionalMiddleware", Value = keyValue});await db.SaveChangesAsync();}await _next(context);} }

使用 MiddlewareFactory 激活的中間件：

public class FactoryActivatedMiddleware : IMiddleware {private readonly AppDbContext _db;public FactoryActivatedMiddleware(AppDbContext db){_db = db;}public async Task InvokeAsync(HttpContext context, RequestDelegate next){var keyValue = context.Request.Query["key"];if (!string.IsNullOrWhiteSpace(keyValue)){_db.Add(new Request(){DT = DateTime.UtcNow, MiddlewareActivation = "FactoryActivatedMiddleware", Value = keyValue});await _db.SaveChangesAsync();}await next(context);} }

程序會為中間件創(chuàng)建擴展：

public static class MiddlewareExtensions {public static IApplicationBuilder UseConventionalMiddleware(this IApplicationBuilder builder){return builder.UseMiddleware<ConventionalMiddleware>();}public static IApplicationBuilder UseFactoryActivatedMiddleware(this IApplicationBuilder builder){return builder.UseMiddleware<FactoryActivatedMiddleware>();} }

無法通過 UseMiddleware 將對象傳遞給工廠激活的中間件：

public static IApplicationBuilder UseFactoryActivatedMiddleware(this IApplicationBuilder builder, bool option) {// Passing 'option' as an argument throws a NotSupportedException at runtime.return builder.UseMiddleware<FactoryActivatedMiddleware>(option); }

將工廠激活的中間件添加到?Startup.ConfigureServices?的內(nèi)置容器中：

public void ConfigureServices(IServiceCollection services) {services.AddDbContext<AppDbContext>(options =>options.UseInMemoryDatabase("InMemoryDb"));services.AddTransient<FactoryActivatedMiddleware>();services.AddRazorPages(); }

兩個中間件均在?Startup.Configure?的請求處理管道中注冊：

public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}else{app.UseExceptionHandler("/Error");}app.UseConventionalMiddleware();app.UseFactoryActivatedMiddleware();app.UseStaticFiles();app.UseRouting();app.UseEndpoints(endpoints =>{endpoints.MapRazorPages();}); }

IMiddlewareFactory

IMiddlewareFactory 提供中間件的創(chuàng)建方法。?中間件工廠實現(xiàn)在容器中注冊為作用域服務(wù)。

可在 Microsoft.AspNetCore.Http 包中找到默認(rèn)的 IMiddlewareFactory 實現(xiàn)（即 MiddlewareFactory）。

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