在啟動ASPNET Core時可以從外部程式集向應用添加增強功能，例如，外部庫可以用托管啟動（ hosting startup） 實作為應用程式提供附加配置（Configuration）或服務（service），
具體實作如下：
1、實作 IHostingStartup 介面
2、標注程式集（HostingStartup）屬性，
[assembly: HostingStartup(typeof(StartupEnhancement.StartupEnhancementHostingStartup))]
3、在CreateHostBuilder中配置加載的程式集，如果多個程式集 分號 隔開
public static IHostBuilder CreateHostBuilder(string[] args) => Host.CreateDefaultBuilder(args) .ConfigureWebHostDefaults(webBuilder => { //增加外部啟動項Fap.Core.DI.ServicesInjection，初始化所有service webBuilder.UseSetting(WebHostDefaults.HostingStartupAssembliesKey,"Fap.Core") .UseStartup<Startup>(); });
如果阻止Hosting Startup加載，需要以下設定
webBuilder.UseSetting(WebHostDefaults.PreventHostingStartupKey, "true")
如果排除某些程式集的Hosting Startup加載
webBuilder.UseSetting(WebHostDefaults.HostingStartupExcludeAssembliesKey, "ASSEMBLY1;ASSEMBLY2; ...")
多個程式集 分號 隔開，
ASPNET Core 中的 DI 沒有批量注冊service的功能，下面我就實作一個批量注冊service的功能，
采用注解的形式，在需要注冊為service的類上進行標注，
定義一個Attribute
[AttributeUsage(AttributeTargets.Class)] public class ServiceAttribute:Attribute { public ServiceAttribute(ServiceLifetime serviceLifetime) { ServiceLifetime = serviceLifetime; } public ServiceLifetime ServiceLifetime { get; set; } = ServiceLifetime.Transient; }
定義需要注冊的類和介面
public interface IUser { string Get(string userName); } public interface IUser1 { string Get1(string userName); } [Service(Microsoft.Extensions.DependencyInjection.ServiceLifetime.Singleton)] public class User : IUser,IUser1 { private string s = Guid.NewGuid().ToString(); public string Get(string userName) { return $"{s}===={userName}"; } public string Get1(string userName) { return s; } }
如上，在User類上標注ServiceAttribute屬性，設定ServiceLifetime為單利模式ServiceLifetime.Singleton
接下來實作 利用host startup來實作自動注冊功能，根據class上標注的service attribute 來自動注冊service
//標注程式集屬性 HostingStartup
[assembly: HostingStartup(typeof(Fap.Core.DI.ServicesInjection))] namespace Fap.Core.DI { public class ServicesInjection : IHostingStartup { public void Configure(IWebHostBuilder builder) { builder.ConfigureServices(services => { var basePath = AppDomain.CurrentDomain.RelativeSearchPath ?? AppDomain.CurrentDomain.BaseDirectory; var assemblies = Directory.GetFiles(basePath, "*.dll").Select(Assembly.LoadFrom).ToArray(); var types = assemblies.SelectMany(a => a.DefinedTypes).Select(type => type.AsType()).Where(t => t.GetCustomAttribute<ServiceAttribute>() != null).ToArray(); var implementTypes = types.Where(t => t.IsClass).ToArray(); foreach (var implementType in implementTypes) { var interfaceTypes = implementType.GetInterfaces(); foreach (var interfaceType in interfaceTypes) { var attr = implementType.GetCustomAttribute<ServiceAttribute>();
//根據serviceLifetime來向容器中注冊 _ = (attr.ServiceLifetime switch { ServiceLifetime sl when sl == ServiceLifetime.Scoped => services.AddScoped(interfaceType, implementType), ServiceLifetime sl when sl == ServiceLifetime.Singleton => services.AddSingleton(interfaceType, implementType), ServiceLifetime sl when sl == ServiceLifetime.Transient => services.AddTransient(interfaceType, implementType), _ => throw new FileNotFoundException("未找到此型別") }); } } }); } } }
下面在Host builder時設定HostStartup
public static IHostBuilder CreateHostBuilder(string[] args) => Host.CreateDefaultBuilder(args) .ConfigureWebHostDefaults(webBuilder => { //增加外部啟動項Fap.Core.DI.ServicesInjection，初始化所有service webBuilder.UseSetting(WebHostDefaults.HostingStartupAssembliesKey,"Fap.Core") .UseStartup<Startup>(); });
這樣我們在Controller中就可以使用已經自動注冊到servicecontainer中的service了，
public class HomeController : Controller { private readonly ILogger<HomeController> _logger; private readonly IUser1 _userService1; private readonly IUser _userService; public HomeController(ILogger<HomeController> logger,IUser1 userService1,IUser user) { _logger = logger; _userService1 = userService1; _userService = user; } public IActionResult Index() { ViewBag.CC = _userService.Get("zhangsan")+_userService1.Get1("lisi"); return View(); } }
除了利用IHostingStartup為應用提供服務注冊，還可以提供額外配置，
[assembly: HostingStartup(typeof(HostingStartupLibrary.ServiceKeyInjection))] namespace HostingStartupLibrary { public class ServiceKeyInjection : IHostingStartup { public void Configure(IWebHostBuilder builder) { builder.ConfigureAppConfiguration(config => { var dict = new Dictionary<string, string> { {"DevAccount_FromLibrary", "DEV_1111111-1111"}, {"ProdAccount_FromLibrary", "PROD_2222222-2222"} }; config.AddInMemoryCollection(dict); }); } } }
在controller中就可以訪問到如上配置項
public IndexModel(IConfiguration config) { ServiceKey_Development_Library = config["DevAccount_FromLibrary"]; ServiceKey_Production_Library = config["ProdAccount_FromLibrary"]; }
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具體原始碼實作：
webBuilder.UseSetting(WebHostDefaults.HostingStartupAssembliesKey,"Fap.Core")
設定了WebHostOptions中的HostingStartupAssemblies屬性，存放我們要加載的IHostingStartup的程式集，
在IWebHostBuilder 呼叫 Builder()回傳IWebHost方法中進行呼叫，下面為關鍵代碼
_options = new WebHostOptions(_config, Assembly.GetEntryAssembly()?.GetName().Name); //沒有設定阻止加載webBuilder.UseSetting( WebHostDefaults.PreventHostingStartupKey, "false") if (!_options.PreventHostingStartup) { var exceptions = new List<Exception>(); // 執行 hosting startup assemblies foreach (var assemblyName in _options.GetFinalHostingStartupAssemblies().Distinct(StringComparer.OrdinalIgnoreCase)) { try { var assembly = Assembly.Load(new AssemblyName(assemblyName)); foreach (var attribute in assembly.GetCustomAttributes<HostingStartupAttribute>()) {
//實體化自定義的hostingStartup var hostingStartup = (IHostingStartup)Activator.CreateInstance(attribute.HostingStartupType);
//呼叫Configure方法，執行我們自定的邏輯 hostingStartup.Configure(this); } } catch (Exception ex) { // Capture any errors that happen during startup exceptions.Add(new InvalidOperationException($"Startup assembly {assemblyName} failed to execute. See the inner exception for more details.", ex)); } } if (exceptions.Count > 0) { hostingStartupErrors = new AggregateException(exceptions); } }
_options.GetFinalHostingStartupAssemblies()方法代碼如下：
public IEnumerable<string> GetFinalHostingStartupAssemblies() {
//回傳HostingStartupAssemblies中排除掉HostingStartupExcludeAssemblies的程式集 return HostingStartupAssemblies.Except(HostingStartupExcludeAssemblies, StringComparer.OrdinalIgnoreCase); }
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標籤：.NET Core
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