asp.net MVC 模型绑定错误"Cannot create an instance of Interface"

Question

我有一个 ViewModel，其接口为属性。当我提交页面时，出现 "Cannot create an instance of Interface" 错误。

ViewModel 是这样的：

public class PlanoPagamentoViewModel
{
     //some properties
     public IPlanoPagamentosParcelas PlanoPagamentosParcelas { get; set; }     
}

有两个类实现了这个接口。根据所选的选项，相应的 ViewModel 会动态加载 PartialView。

public class PlanoPagamentoCartaoViewModel : IPlanoPagamentosParcelas
{
   //some properties
}

public class PlanoPagamentoCrediarioViewModel : IPlanoPagamentosParcelas
{
   //some properties
}

我进行了一项研究，发现需要创建自定义模型绑定，然后我就这样做了：

public class PlanoPagamentoParcelasBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        var type = typeof(PlanoPagamentoCartaoViewModel);
        var model = Activator.CreateInstance(type);
        bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, type);

        return model;
    }
}

并在 Global.asax、Application_Start 方法中添加这个新的自定义绑定：

ModelBinders.Binders.Add(typeof(IPlanoPagamentosParcelas), new PlanoPagamentoParcelasBinder());

它适用于 PlanoPagamentoCartaoViewModel，但我需要为 PlanoPagamentoCrediarioViewModel 设置另一个自定义绑定，但我不能只添加一个具有相同密钥的新 ModelBinders.Binders.Add (IPlanoPagamentosParcelas) 因为已经有一把这种类型的钥匙。

那么，是否有任何其他方法可以为实现相同接口的 ViewModel 创建自定义模型绑定？

Answer 1

我认为解决方案如下：

protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
{
        var typeValueProvider = bindingContext.ValueProvider.GetValue("Type");

        var type = (int)typeValueProvider.ConvertTo(typeof(int));

        Type instanceType = null;

        switch (type)
        {
            case 1:
                instanceType = typeof(PlanoPagamentoCartaoViewModel );
                break;

            case 2:
                instanceType = typeof(PlanoPagamentoCrediarioViewModel );
                break;
        }

        if (!typeof(IPlanoPagamentosParcelas).IsAssignableFrom(instanceType))
        {
            throw new InvalidOperationException("Bad Type");
        }
        var model = Activator.CreateInstance(instanceType);
        bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, instanceType);
        return model;
}

在上面的代码中，var typeValueProvider = bindingContext.ValueProvider.GetValue("Type"); Type 将决定实例化哪个具体 class。我测试了这个解决方案，它对我有用。它可以改进为更具可扩展性（也许删除其他东西的开关）但我只是试图让它工作。

这是我提出问题的依据（也许您可以从那里获得更多信息）Polymorphic model binding 下面是我为模拟这种情况而创建的代码（以防万一）：

型号：

public class NewVehicleViewModel
{
    public string Type { get; set; }

    public VehicleViewModel Vehicle { get; set; }
}

public interface VehicleViewModel
{
    string Name { get; set; }
    string Color { get; set; }
}

public class CarViewModel : VehicleViewModel
{
    public string Color { get; set; }

    public string Name { get; set; }

    public string Brand { get; set; }
}

public class TankViewModel : VehicleViewModel
{
    public string Color { get; set; }

    public string Name { get; set; }

    public string Weapon { get; set; }
}

活页夹：

public class VehicleBinder : DefaultModelBinder
{
    protected override object CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)
    {
        var typeValueProvider = bindingContext.ValueProvider.GetValue("Type");

        var type = (int)typeValueProvider.ConvertTo(typeof(int));

        Type instanceType = null;

        switch (type)
        {
            case 1:
                instanceType = typeof(CarViewModel);
                break;

            case 2:
                instanceType = typeof(TankViewModel);
                break;
        }

        if (!typeof(VehicleViewModel).IsAssignableFrom(instanceType))
        {
            throw new InvalidOperationException("Bad Type");
        }
        var model = Activator.CreateInstance(instanceType);
        bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, instanceType);
        return model;
    }
}

控制器：

public class VehiclesController : Controller
{
    // GET: Vehicles
    public ActionResult Index()
    {
        return View();
    }

    [HttpPost]
    public ActionResult Create(NewVehicleViewModel vm)
    {
        return View();
    }
}

GLOBAL.ASAX:

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
        BundleConfig.RegisterBundles(BundleTable.Bundles);
        ModelBinders.Binders.Add(typeof(VehicleViewModel), new VehicleBinder());
    }

VIEW (Index.cshtml):

@{
    ViewBag.Title = "New Vehicle";
}


@using (Html.BeginForm("Create", "Vehicles"))
{
    <label>Type</label>
    <input name="type" type="text" />

    <label >Name</label>
    <input name="Vehicle.Name" type="text"/>

    <label>Color</label>
    <input name="Vehicle.Color" type="text" />

    <label>Weapon</label>
    <input name="Vehicle.Weapon" type="text" />

    <label>Brand</label>
    <input name="Vehicle.Brand" type="text" />

    <input type="submit" />
}

此致。

asp.net MVC 模型绑定错误"Cannot create an instance of Interface"

asp.net MVC model binding error "Cannot create an instance of Interface"

c#

asp.net-mvc

model-binding