我一直试图在ASP.NET Core 2中为抽象类实现模型绑定器而没有成功。
我研究了两篇特别好看的文章：
http://www.dotnetcurry.com/aspnet-mvc/1368/aspnet-core-mvc-custom-model-binding
Asp net core rc2. Abstract class model binding
我试图达到两个目标，
这是我的代码基于上面提到的文章。
public class Trigger
{
public ActionBase Action { get; set; }
}
[ModelBinder(BinderType = typeof(ActionModelBinder))]
public abstract class ActionBase
{
public string Type => GetType().FullName;
public ActionBase Action { get; set; }
}
public class ActionA : ActionBase
{
public int IntProperty { get; set; }
}
public class ActionB : ActionBase
{
public string StringProperty { get; set; }
}
public class ActionModelBinderProvider : IModelBinderProvider
{
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context == null)
throw new ArgumentNullException(nameof(context));
if (context.Metadata.ModelType != typeof(ActionBase))
return null;
var binders = new Dictionary<string, IModelBinder>();
foreach (var type in typeof(ActionModelBinderProvider).GetTypeInfo().Assembly.GetTypes())
{
var typeInfo = type.GetTypeInfo();
if (typeInfo.IsAbstract || typeInfo.IsNested)
continue;
if (!(typeInfo.IsClass && typeInfo.IsPublic))
continue;
if (!typeof(ActionBase).IsAssignableFrom(type))
continue;
var metadata = context.MetadataProvider.GetMetadataForType(type);
var binder = context.CreateBinder(metadata); // This is a BinderTypeModelBinder
binders.Add(type.FullName, binder);
}
return new ActionModelBinder(context.MetadataProvider, binders);
}
}
public class ActionModelBinder : IModelBinder
{
private readonly IModelMetadataProvider _metadataProvider;
private readonly Dictionary<string, IModelBinder> _binders;
public ActionModelBinder(IModelMetadataProvider metadataProvider, Dictionary<string, IModelBinder> binders)
{
_metadataProvider = metadataProvider;
_binders = binders;
}
public async Task BindModelAsync(ModelBindingContext bindingContext)
{
var messageTypeModelName = ModelNames.CreatePropertyModelName(bindingContext.ModelName, "Type");
var messageTypeResult = bindingContext.ValueProvider.GetValue(messageTypeModelName);
if (messageTypeResult == ValueProviderResult.None)
{
bindingContext.Result = ModelBindingResult.Failed();
return;
}
IModelBinder binder;
if (!_binders.TryGetValue(messageTypeResult.FirstValue, out binder))
{
bindingContext.Result = ModelBindingResult.Failed();
return;
}
// Now know the type exists in the assembly.
var type = Type.GetType(messageTypeResult.FirstValue);
var metadata = _metadataProvider.GetMetadataForType(type);
ModelBindingResult result;
using (bindingContext.EnterNestedScope(metadata, bindingContext.FieldName, bindingContext.ModelName, model: null))
{
await binder.BindModelAsync(bindingContext);
result = bindingContext.Result;
}
bindingContext.Result = result;
}
}
编辑器模板放置在正确的位置：
ActionA.cshtml
@model WebApplication1.Models.ActionA
<div class="row">
<h4>Action A</h4>
<div class="col-md-4">
<div class="form-group">
<label asp-for="IntProperty" class="control-label"></label>
<input asp-for="IntProperty" class="form-control" />
<span asp-validation-for="IntProperty" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Type" class="control-label"></label>
</div>
@Html.EditorFor(x => x.Action)
</div>
</div>
ActionB.cshtml
@model WebApplication1.Models.ActionB
<div class="row">
<h4>Action B</h4>
<div class="col-md-4">
<div class="form-group">
<label asp-for="StringProperty" class="control-label"></label>
<input asp-for="StringProperty" class="form-control" />
<span asp-validation-for="StringProperty" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Type" class="control-label"></label>
</div>
@Html.EditorFor(x => x.Action)
</div>
</div>
Index.cshtml
@model WebApplication1.Models.Trigger
<h2>Edit</h2>
<h4>Trigger</h4>
<hr />
<div class="row">
<div class="col-md-4">
<form asp-action="Index">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
@Html.EditorFor(x=>x.Action)
<div class="form-group">
<input type="submit" value="Save" class="btn btn-default" />
</div>
</form>
</div>
</div>
HomeController.cshtml
public class HomeController : Controller
{
public IActionResult Index()
{
var trigger = new Trigger()
{
Action = new ActionA()
{
IntProperty = 1,
Action = new ActionB()
{
StringProperty = "foo"
}
}
};
return View(trigger);
}
[HttpPost]
public IActionResult Index(Trigger model)
{
return View(model);
}
}
关于目标号码。 1只渲染第一个动作，即使它有一个子动作。
当试图发回（目标2）时，我得到一个例外：
InvalidOperationException：无法解析类型＆System; System.Collections.Generic.Dictionary`2 [System.String，Microsoft.AspNetCore.Mvc.ModelBinding.IModelBinder]＆＃39;的服务。在尝试激活WebApplication1.ActionModelBinder＆＃39;。
时
非常感谢对此的任何帮助！
答案 0 :(得分：3)
我错误地将ModelBinder属性添加到我想要执行自定义绑定的类中。
[ModelBinder(BinderType = typeof(ActionModelBinder))]
public abstract class ActionBase
{
public string Type => GetType().FullName;
public ActionBase Action { get; set; }
}
这导致绕过提供者代码 - 删除此属性解决了几个问题。
我重构了提供者和活页夹是通用的，所以不需要重复代码。
public class AbstractModelBinderProvider<T> : IModelBinderProvider where T : class
{
public IModelBinder GetBinder(ModelBinderProviderContext context)
{
if (context == null)
throw new ArgumentNullException(nameof(context));
if (context.Metadata.ModelType != typeof(T))
return null;
var binders = new Dictionary<string, IModelBinder>();
foreach (var type in typeof(AbstractModelBinderProvider<>).GetTypeInfo().Assembly.GetTypes())
{
var typeInfo = type.GetTypeInfo();
if (typeInfo.IsAbstract || typeInfo.IsNested)
continue;
if (!(typeInfo.IsClass && typeInfo.IsPublic))
continue;
if (!typeof(T).IsAssignableFrom(type))
continue;
var metadata = context.MetadataProvider.GetMetadataForType(type);
var binder = context.CreateBinder(metadata);
binders.Add(type.FullName, binder);
}
return new AbstractModelBinder(context.MetadataProvider, binders);
}
}
public class AbstractModelBinder : IModelBinder
{
private readonly IModelMetadataProvider _metadataProvider;
private readonly Dictionary<string, IModelBinder> _binders;
public AbstractModelBinder(IModelMetadataProvider metadataProvider, Dictionary<string, IModelBinder> binders)
{
_metadataProvider = metadataProvider;
_binders = binders;
}
public async Task BindModelAsync(ModelBindingContext bindingContext)
{
var messageTypeModelName = ModelNames.CreatePropertyModelName(bindingContext.ModelName, "Type");
var typeResult = bindingContext.ValueProvider.GetValue(messageTypeModelName);
if (typeResult == ValueProviderResult.None)
{
bindingContext.Result = ModelBindingResult.Failed();
return;
}
IModelBinder binder;
if (!_binders.TryGetValue(typeResult.FirstValue, out binder))
{
bindingContext.Result = ModelBindingResult.Failed();
return;
}
var type = Type.GetType(typeResult.FirstValue);
var metadata = _metadataProvider.GetMetadataForType(type);
ModelBindingResult result;
using (bindingContext.EnterNestedScope(metadata, bindingContext.FieldName, bindingContext.ModelName, model: null))
{
await binder.BindModelAsync(bindingContext);
result = bindingContext.Result;
}
bindingContext.Result = result;
return;
}
}
在配置中注册提供者：
services.AddMvc(opts =>
{
opts.ModelBinderProviders.Insert(0, new AbstractModelBinderProvider<ActionViewModel>());
opts.ModelBinderProviders.Insert(0, new AbstractModelBinderProvider<TriggerViewModel>());
});
如果要处理许多抽象类，还可以更改AbstractModelBinderProvider以接受要处理的参数化类型集合而不是泛型类型以减少提供程序的数量。
关于能够窝儿的问题，必须注意一些限制。
请参阅：In an Editor Template call another Editor Template with the same Model
简短的回答是使用部分代码，如下所示：
@model ActionViewModel
@if (Model == null)
{
return;
}
<div class="actionRow">
@using (Html.BeginCollectionItem("Actions"))
{
<input type="hidden" asp-for="Type" />
<input type="hidden" asp-for="Id" />
if (Model is CustomActionViewModel)
{
@Html.Partial("EditorTemplates/CustomAction", Model);
}
}
</div>
BeginCollectionItem是一个html助手。