如何在不全局设置的情况下使用自定义的ASP.NET MVC IValueProvider？

Question

我想要能够从cookie中获取键/值对并用它来绑定模型。相比建立一个自定义的ModelBinder，我认为DefaultModelBinder已经可以很好地使用了，而且选择值来自哪里的最佳方式是设置它所使用的IValueProvider。

为了实现这一点，我不想创建一个自定义的ValueProviderFactory并将其全局绑定，因为我只想在特定的操作方法中使用这个ValueProvider。

我已经编写了一个属性来实现这个功能：

/// <summary>
/// Replaces the current value provider with the specified value provider
/// </summary>
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class, Inherited = true, AllowMultiple = true)]
public class SetValueProviderAttribute : ActionFilterAttribute
{
    public SetValueProviderAttribute(Type valueProviderType)
    {
        if (valueProviderType.GetInterface(typeof(IValueProvider).Name) == null)
            throw new ArgumentException("Type " + valueProviderType + " must implement interface IValueProvider.", "valueProviderType");

        _ValueProviderType = valueProviderType;
    }

    private Type _ValueProviderType;

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        IValueProvider valueProviderToAdd = GetValueProviderToAdd();

        filterContext.Controller.ValueProvider = valueProviderToAdd;
    }

    private IValueProvider GetValueProviderToAdd()
    {
        return (IValueProvider)Activator.CreateInstance(_ValueProviderType);
    }
}

很遗憾，ModelBinder及其IValueProvider在OnActionExecuting之前设置（为什么？？？）。是否有其他人想出了一种方法，在不使用ValueProviderFactory的情况下向DefaultModelBinder注入自定义的IValueProvider？

- Oved D

Answer 1

在这种情况下，您仍应使用ValueProviderFactory。

您需要在ValueProviderFactory上实现的方法具有以下签名：

IValueProvider GetValueProvider(ControllerContext controllerContext)

在该方法的实现中，您可以检查控制器上下文，如果传入请求是要使用cookie的控制器/操作，则返回一些 CustomCookieValueProvider。

如果您不想在请求中使用cookie，只需返回 null，框架将过滤掉该值提供程序列表中的选项。

作为额外的奖励，您可能不想将何时使用 CustomCookieValueProvider 的逻辑硬编码到 ValueProviderFactory 中。也许可以利用 DataTokens 来匹配是否针对给定路由使用cookie。因此，添加如下路由：

routes.MapRoute("SomeRoute","{controller}/{action}").DataTokens.Add("UseCookies", true);

请注意其中的DataTokens.Add()调用，现在在您的GetValueProvider方法内部，您可以执行以下操作：

if (controllerContext.RouteData.DataTokens.ContainsKey("UseCookies"))
{
    return new CustomCookieValueProvider(controllerContext.RequestContext.HttpContext.Request.Cookies);
}

return null;

- nikmd23

---

我明白为什么@Oved D希望将其作为属性。但是DataTokens解决方案非常优雅。 - Oli

Answer 2

这里有一个替代方案，可以让您在操作参数上指定IValueProviders作为属性。这使得IValueProviders是短暂的而不是全局的。

public interface IControllerContextAware
{
    ControllerContext ControllerContext { get; set; }
}

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Parameter, AllowMultiple = false, Inherited = false)]
public class ValueProviderAttribute : CustomModelBinderAttribute
{
    public Type[] ValueProviders { get; private set; }

    public ValueProviderAttribute(params Type[] valueProviders)
    {
        if (valueProviders == null)
        {
            throw new ArgumentNullException("valueProviders");
        }
        foreach (var valueProvider in valueProviders.Where(valueProvider => !typeof(IValueProvider).IsAssignableFrom(valueProvider)))
        {
            throw new ArgumentException(string.Format(CultureInfo.CurrentCulture, "The valueProvider {0} must be of type {1}", valueProvider.FullName, typeof(IValueProvider)), "valueProviders");
        }

        ValueProviders = valueProviders;
    }

    public override IModelBinder GetBinder()
    {
        return new ValueProviderModelBinder
            {
                ValueProviderTypes = ValueProviders.ToList(),
                CreateValueProvider = OnCreateValueProvider
            };
    }

    protected virtual IValueProvider OnCreateValueProvider(Type valueProviderType, ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var valueProvider = (IValueProvider)Activator.CreateInstance(valueProviderType);
        if (valueProvider is IControllerContextAware)
        {
            (valueProvider as IControllerContextAware).ControllerContext = controllerContext;
        }
        return valueProvider;
    }

    private class ValueProviderModelBinder : DefaultModelBinder
    {
        public IList<Type> ValueProviderTypes { get; set; }
        public Func<Type, ControllerContext, ModelBindingContext, IValueProvider> CreateValueProvider { get; set; }

        public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            var valueProviders = from type in ValueProviderTypes
                                 select CreateValueProvider(type, controllerContext, bindingContext);

            bindingContext.ValueProvider = new ValueProviderCollection(valueProviders.Concat((Collection<IValueProvider>)bindingContext.ValueProvider).ToList());

            return base.BindModel(controllerContext, bindingContext);
        }
    }
}

这基本上是ModelBinderAttribute的代码形式，但有一些修改。它不是密封的，因此如果需要，您可以更改创建IValueProviders的方式。

这里有一个简单的示例，它查找另一个字段（可能是隐藏或加密字段），并将数据放入另一个属性中。

这是一个模型，它不知道IValueProvider，但知道隐藏字段。

public class SomeModel
{
    [Required]
    public string MyString { get; set; }

    [Required]
    public string MyOtherString { get; set; }

    [Required]
    public string Data { get; set; }
}

然后我们有IValueProvider，在这种情况下，我的提供程序明确知道我的模型，但这并不一定是这种情况。

public class MyValueProvider : IValueProvider, IControllerContextAware
{
    public ControllerContext ControllerContext { get; set; }

    public bool ContainsPrefix(string prefix)
    {
        var containsPrefix = prefix == "MyString" && ControllerContext.HttpContext.Request.Params.AllKeys.Any(key => key == "Data");
        return containsPrefix;
    }

    public ValueProviderResult GetValue(string key)
    {
        if (key == "MyString")
        {
            var data = ControllerContext.RequestContext.HttpContext.Request.Params["Data"];

            var myString = data.Split(':')[1];

            return new ValueProviderResult(myString, myString, CultureInfo.CurrentCulture);
        }
        return null;
    }
}

然后是将所有这些联系起来的操作：

    [HttpGet]
    public ActionResult Test()
    {
        return View(new SomeModel());
    }

    [HttpPost]
    public ActionResult Test([ValueProvider(typeof(MyValueProvider))]SomeModel model)
    {
        return View(model);
    }

- Dewy

Answer 3

研究出如何做到这一点。 首先，创建一个自定义模型绑定器，在构造函数中采用值提供程序类型 - 但从默认模型绑定器继承。 这使您可以使用自定义值提供程序的标准模型绑定：

/// <summary>
/// Uses default model binding, but sets the value provider it uses
/// </summary>
public class SetValueProviderDefaultModelBinder : DefaultModelBinder
{
    private Type _ValueProviderType;

    public SetValueProviderDefaultModelBinder(Type valueProviderType)
    {
        if (valueProviderType.GetInterface(typeof(IValueProvider).Name) == null)
            throw new ArgumentException("Type " + valueProviderType + " must implement interface IValueProvider.", "valueProviderType");

        _ValueProviderType = valueProviderType;
    }

    /// <summary>
    /// Before binding the model, set the IValueProvider it uses
    /// </summary>
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        bindingContext.ValueProvider = GetValueProvider();

        return base.BindModel(controllerContext, bindingContext);
    }

    private IValueProvider GetValueProvider()
    {
        return (IValueProvider)Activator.CreateInstance(_ValueProviderType);
    }
}

然后我们创建一个模型绑定属性，将以上创建的自定义模型绑定器中的值提供程序类型注入其中，并将其用作模型绑定器：

/// <summary>
/// On the default model binder, replaces the current value provider with the specified value provider.  Cannot use custom model binder with this.
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Class | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Parameter | AttributeTargets.Struct, AllowMultiple = false, Inherited = false)]
public class SetValueProviderAttribute : CustomModelBinderAttribute
{
    // Originally, this was an action filter, that OnActionExecuting, set the controller's IValueProvider, expecting it to be picked up by the default model binder
    // when binding the model.  Unfortunately, OnActionExecuting occurs AFTER the IValueProvider is set on the DefaultModelBinder.  The only way around this is
    // to create a custom model binder that inherits from DefaultModelBinder, and in its BindModel method set the ValueProvider and then do the standard model binding.

    public SetValueProviderAttribute(Type valueProviderType)
    {
        if (valueProviderType.GetInterface(typeof(IValueProvider).Name) == null)
            throw new ArgumentException("Type " + valueProviderType + " must implement interface IValueProvider.", "valueProviderType");

        _ValueProviderType = valueProviderType;
    }

    private Type _ValueProviderType;

    public override IModelBinder GetBinder()
    {
        var modelBinder = new SetValueProviderDefaultModelBinder(_ValueProviderType);
        return modelBinder;
    }
}

- Oved D