现在我的ViewModel看起来像这样：
public class MyViewModel
{
private readonly IMyService myService;
public ClaimantSearchViewModel(IMyService myService)
{
this.myService = myService;
}
}
我消耗此ViewModel的Controller如下所示：
public class MyController : Controller
{
private readonly IMyService myService;
public HomeController(IMyService myService)
{
this.myService = myService;
}
public IActionResult Index()
{
var model = new MyViewModel(myService);
return View(model);
}
[HttpPost]
public async Task<IActionResult> Find()
{
var model = new MyViewModel(myService);
await TryUpdateModelAsync(model);
return View("Index", model);
}
}
我需要的是我的Controller看起来像这样：
public class MyController : Controller
{
private readonly IServiceProvider servicePovider;
public MyController(IServiceProvider servicePovider)
{
this.servicePovider = servicePovider;
}
public IActionResult Index()
{
var model = servicePovider.GetService(typeof(MyViewModel));
return View(model);
}
[HttpPost]
public IActionResult Index(MyViewModel model)
{
return View(model);
}
}
现在，调用第一个Index方法工作正常（使用
builder.RegisterSource(new AnyConcreteTypeNotAlreadyRegisteredSource(x => x.Name.Contains("ViewModel")));
在我的Startup class中），但是POST Index(MyViewModel model)会给你一个No parameterless constructor defined for this object例外。我意识到可以使用我的DI custom model binder将是最有可能的解决方案......但我甚至无法找到有关如何从这里开始的任何帮助。请帮助我解决这个问题，特别是对于MVC 6的Autofac.
我们在这里得到了答案：https://github.com/aspnet/Mvc/issues/4167
答案是使用：[来自服务]
我的模型最终看起来像这样：
public class MyViewModel
{
[FromServices]
public IMyService myService { get; set; }
public ClaimantSearchViewModel(IMyService myService)
{
this.myService = myService;
}
}
虽然让该属性public很难过，但这比不得不使用custom model binder要难过得多。
此外，据说您应该能够将[FromServices]作为 Action 方法中的参数的一部分传递，它确实解析了类，但这会破坏模型绑定......即我的财产都没有被映射。它看起来像这样：（但同样，这不起作用，所以使用上面的例子）
public class MyController : Controller
{
... same as in OP
[HttpPost]
public IActionResult Index([FromServices]MyViewModel model)
{
return View(model);
}
}
更新 1
在使用 [FromServices ] 属性后，我们决定在所有ViewModels中注入属性不是我们想要的方式，尤其是在考虑通过测试进行长期维护时。因此，我们决定删除[FromServices]属性，并使我们的自定义模型绑定器正常工作：
public class IoCModelBinder : IModelBinder
{
public Task<ModelBindingResult> BindModelAsync(ModelBindingContext bindingContext)
{
var serviceProvider = bindingContext.OperationBindingContext.HttpContext.RequestServices;
var model = serviceProvider.GetService(bindingContext.ModelType);
bindingContext.Model = model;
var binder = new GenericModelBinder();
return binder.BindModelAsync(bindingContext);
}
}
它在Startup ConfigureServices方法中注册如下：
services.AddMvc().AddMvcOptions(options =>
{
options.ModelBinders.Clear();
options.ModelBinders.Add(new IoCModelBinder());
});
仅此而已。（甚至不确定是否需要options.ModelBinders.Clear();。
更新 2在经历了各种迭代使其工作（在 https://github.com/aspnet/Mvc/issues/4196 的帮助下）之后，这是最终结果：
public class IoCModelBinder : IModelBinder
{
public async Task<ModelBindingResult> BindModelAsync(ModelBindingContext bindingContext)
{ // For reference: https://github.com/aspnet/Mvc/issues/4196
if (bindingContext == null)
throw new ArgumentNullException(nameof(bindingContext));
if (bindingContext.Model == null && // This binder only constructs viewmodels, avoid infinite recursion.
(
(bindingContext.ModelType.Namespace.StartsWith("OUR.SOLUTION.Web.ViewModels") && bindingContext.ModelType.IsClass)
||
(bindingContext.ModelType.IsInterface)
)
)
{
var serviceProvider = bindingContext.OperationBindingContext.HttpContext.RequestServices;
var model = serviceProvider.GetRequiredService(bindingContext.ModelType);
// Call model binding recursively to set properties
bindingContext.Model = model;
var result = await bindingContext.OperationBindingContext.ModelBinder.BindModelAsync(bindingContext);
bindingContext.ValidationState[model] = new ValidationStateEntry() { SuppressValidation = true };
return result;
}
return await ModelBindingResult.NoResultAsync;
}
}
您显然希望将OUR.SOLUTION...替换为适合您的ViewModels的任何namespace 我们的注册：
services.AddMvc().AddMvcOptions(options =>
{
options.ModelBinders.Insert(0, new IoCModelBinder());
});
更新 3：这是Model Binder及其Provider的最新版本，适用于ASP.NET Core 2.X：
public class IocModelBinder : ComplexTypeModelBinder
{
public IocModelBinder(IDictionary<ModelMetadata, IModelBinder> propertyBinders, ILoggerFactory loggerFactory) : base(propertyBinders, loggerFactory)
{
}
protected override object CreateModel(ModelBindingContext bindingContext)
{
object model = bindingContext.HttpContext.RequestServices.GetService(bindingContext.ModelType) ?? base.CreateModel(bindingContext);
if (bindingContext.HttpContext.Request.Method == "GET")
bindingContext.ValidationState[model] = new ValidationStateEntry { SuppressValidation = true };
return model;
}
}
public class IocModelBinderProvider : IModelBinderProvider
{
private readonly ILoggerFactory loggerFactory;
public IocModelBinderProvider(ILoggerFactory loggerFactory)
{
this.loggerFactory = loggerFactory;
}
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (!context.Metadata.IsComplexType || context.Metadata.IsCollectionType) return null;
var propertyBinders = new Dictionary<ModelMetadata, IModelBinder>();
foreach (ModelMetadata property in context.Metadata.Properties)
{
propertyBinders.Add(property, context.CreateBinder(property));
}
return new IocModelBinder(propertyBinders, loggerFactory);
}
}
然后在Startup：
services.AddMvc(options =>
{
// add IoC model binder.
IModelBinderProvider complexBinder = options.ModelBinderProviders.FirstOrDefault(x => x.GetType() == typeof(ComplexTypeModelBinderProvider));
int complexBinderIndex = options.ModelBinderProviders.IndexOf(complexBinder);
options.ModelBinderProviders.RemoveAt(complexBinderIndex);
options.ModelBinderProviders.Insert(complexBinderIndex, new IocModelBinderProvider(loggerFactory));
这个问题被标记为 ASP.NET Core，所以这是我们针对 dotnet core 3.1 的解决方案。
我们的解决方案概述：TheProject 需要使ICustomerService可用于在请求管道中自动创建的对象。需要此功能的类使用接口 IUsesCustomerService 标记。然后，Binder 在创建对象时检查此接口，并处理特殊情况。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.Extensions.Logging;
namespace TheProject.Infrastructure.DependencyInjection
{
/// <summary>
/// This is a simple pass through class to the binder class.
/// It gathers some information from the context and passes it along.
/// </summary>
public class TheProjectModelBinderProvider : IModelBinderProvider
{
public TheProjectModelBinderProvider()
{
}
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
ILoggerFactory ilogger;
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
// The Binder that gets returned is a <ComplexTypeModelBinder>, but I'm
// not sure what side effects returning early here might cause.
if (!context.Metadata.IsComplexType || context.Metadata.IsCollectionType)
{
return null;
}
var propertyBinders = new Dictionary<ModelMetadata, IModelBinder>();
foreach (ModelMetadata property in context.Metadata.Properties)
{
propertyBinders.Add(property, context.CreateBinder(property));
}
ilogger = (ILoggerFactory)context.Services.GetService(typeof(ILoggerFactory));
return new TheProjectModelBinder(propertyBinders, ilogger);
}
}
/// <summary>
/// Custom model binder.
/// Allows interception of endpoint method to adjust object construction
/// (allows automatically setting properties on an object that ASP.NET creates for the endpoint).
/// Here this is used to make sure the <see cref="ICustomerService"/> is set correctly.
/// </summary>
public class TheProjectModelBinder : ComplexTypeModelBinder
{
public TheProjectModelBinder(IDictionary<ModelMetadata, IModelBinder> propertyBinders, ILoggerFactory loggerFactory)
: base(propertyBinders, loggerFactory)
{
}
/// <summary>
/// Method to construct an object. This normally calls the default constructor.
/// This method does not set property values, setting those are handled elsewhere in the pipeline,
/// with the exception of any special properties handled here.
/// </summary>
/// <param name="bindingContext">Context.</param>
/// <returns>Newly created object.</returns>
protected override object CreateModel(ModelBindingContext bindingContext)
{
if (bindingContext == null)
throw new ArgumentNullException(nameof(bindingContext));
var customerService = (ICustomerService)bindingContext.HttpContext.RequestServices.GetService(typeof(ICustomerService));
bool setcustomerService = false;
object model;
if (typeof(IUsesCustomerService).IsAssignableFrom(bindingContext.ModelType))
{
setcustomerService = true;
}
// I think you can also just call Activator.CreateInstance here.
// The end result is an object that's constructed, but no properties are set yet.
model = base.CreateModel(bindingContext);
if (setcustomerService)
{
((IUsesCustomerService)model).SetcustomerService(customerService);
}
return model;
}
}
}
然后在启动代码中，确保设置AddMvcOptions 。
public void ConfigureServices(IServiceCollection services)
{
// ...
// asp.net core 3.1 MVC setup
services.AddControllersWithViews()
.AddApplicationPart(assembly)
.AddRazorRuntimeCompilation()
.AddMvcOptions(options =>
{
IModelBinderProvider complexBinder = options.ModelBinderProviders.FirstOrDefault(x => x.GetType() == typeof(ComplexTypeModelBinderProvider));
int complexBinderIndex = options.ModelBinderProviders.IndexOf(complexBinder);
options.ModelBinderProviders.RemoveAt(complexBinderIndex);
options.ModelBinderProviders.Insert(complexBinderIndex, new Infrastructure.DependencyInjection.TheProjectModelBinderProvider());
});
}