asp.net core mvc 2 中抽象类的模型绑定器

Question

我一直在尝试为 ASP.NET Core 2 中的抽象类实现模型绑定程序，但没有成功。

我特别研究了两篇看起来非常好的文章：

http://www.dotnetcurry.com/aspnet-mvc/1368/aspnet-core-mvc-custom-model-binding

Asp 网络核心 rc2. 抽象类模型绑定

我有两个目标正在努力实现

1. 根据模型的需要自动创建任意数量的嵌套编辑器（子嵌套）。
2. 将表单值正确映射回模型。

这是我基于上述文章的代码。

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>

索引.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);
    }
}

关于目标没有。1 仅渲染第一个动作，即使它有子动作。

当尝试回发（目标 2）时，我遇到了一个异常：

InvalidOperationException：尝试激活“WebApplication1.ActionModelBinder”时无法解析类型“System.Collections.Generic.Dictionary`2[System.String,Microsoft.AspNetCore.Mvc.ModelBinding.IModelBinder]”的服务。

非常感谢对此的任何帮助！

Answer 1

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; }
}

这导致提供程序代码被绕过 - 删除此属性解决了几个问题。

我将提供程序和绑定程序重构为通用的，因此无需重复代码。

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;
    }
}

并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>());
});

如果有许多抽象类需要处理，还可以更改 AbstractModelBinderProvider 以接受要处理的参数化类型集合而不是通用类型，以减少提供程序的数量。

关于能够为孩子筑巢，必须注意一些限制。

请参阅：在编辑器模板中调用具有相同模型的另一个编辑器模板

简短的答案是使用部分代替，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>

这BeginCollectionItem是一个 html 帮助器。

请参阅： https: //github.com/danludwig/BeginCollectionItem

并且： https: //github.com/saad749/BeginCollectionItemCore