ASP.NET Core 中文文档 第四章 MVC（4.4）依赖注入和控制器

依赖注入

构造器注入

using System;

namespace ControllerDI.Interfaces
{
public interface IDateTime
{
DateTime Now { get; }
}
}

using System;
using ControllerDI.Interfaces;

namespace ControllerDI.Services
{
public class SystemDateTime : IDateTime
{
public DateTime Now
{
get { return DateTime.Now; }
}
}
}

HomeController

Index

using ControllerDI.Interfaces;
using Microsoft.AspNetCore.Mvc;

namespace ControllerDI.Controllers
{
public class HomeController : Controller
{
private readonly IDateTime _dateTime;   //手动高亮

public HomeController(IDateTime dateTime)   //手动高亮
{
_dateTime = dateTime;   //手动高亮
}

public IActionResult Index()
{
var serverTime = _dateTime.Now; //手动高亮
if (serverTime.Hour < 12)       //手动高亮
{
ViewData["Message"] = "It's morning here - Good Morning!";  //手动高亮
}
else if (serverTime.Hour < 17)  //手动高亮
{
ViewData["Message"] = "It's afternoon here - Good Afternoon!";  //手动高亮
}
else    //手动高亮
{
ViewData["Message"] = "It's evening here - Good Evening!";  //手动高亮
}
return View();  //手动高亮
}
}
}

An unhandled exception occurred while processing the request.

InvalidOperationException: Unable to resolve service for type 'ControllerDI.Interfaces.IDateTime' while attempting to activate 'ControllerDI.Controllers.HomeController'.
Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)

Startup

ConfigureServices

IDateTime

SystemDateTime

ConfigureServices

public void ConfigureServices(IServiceCollection services)
{
// Add application services.
services.AddTransient<IDateTime, SystemDateTime>();     //手动高亮
}

Transient

Scoped

Singleton

An unhandled exception occurred while processing the request.

InvalidOperationException: Multiple constructors accepting all given argument types have been found in type 'ControllerDI.Controllers.HomeController'. There should only be one applicable constructor.
Microsoft.Extensions.DependencyInjection.ActivatorUtilities.FindApplicableConstructor(Type instanceType, Type[] argumentTypes, ConstructorInfo& matchingConstructor, Nullable`1[]& parameterMap)

Action 注入和 FromServices

[FromServices]

public IActionResult About([FromServices] IDateTime dateTime)   //手动高亮
{
ViewData["Message"] = "Currently on the server the time is " + dateTime.Now;

return View();
}

从控制器访问设置

IOptions<T>

T

namespace ControllerDI.Model
{
public class SampleWebSettings
{
public string Title { get; set; }
public int Updates { get; set; }
}
}

ConfigureServices

public Startup(IHostingEnvironment env)
{
var builder = new ConfigurationBuilder()    //手动高亮
.SetBasePath(env.ContentRootPath)       //手动高亮
.AddJsonFile("samplewebsettings.json"); //手动高亮
Configuration = builder.Build();            //手动高亮
}

public IConfigurationRoot Configuration { get; set; }   //手动高亮

// This method gets called by the runtime. Use this method to add services to the container.
// For more information on how to configure your application, visit http://go.microsoft.com/fwlink/?LinkID=398940 public void ConfigureServices(IServiceCollection services)
{
// Required to use the Options<T> pattern
services.AddOptions();      //手动高亮

// Add settings from configuration
services.Configure<SampleWebSettings>(Configuration);   //手动高亮

// Uncomment to add settings from code
//services.Configure<SampleWebSettings>(settings =>
//{
//    settings.Updates = 17;
//});

services.AddMvc();

// Add application services.
services.AddTransient<IDateTime, SystemDateTime>();
}

SampleWebSettings

IOptions<T>

IOptions<SampleWebSettings>

public class SettingsController : Controller
{
private readonly SampleWebSettings _settings;   //手动高亮

public SettingsController(IOptions<SampleWebSettings> settingsOptions)  //手动高亮
{
_settings = settingsOptions.Value;  //手动高亮
}

public IActionResult Index()
{
ViewData["Title"] = _settings.Title;
ViewData["Updates"] = _settings.Updates;
return View();
}
}