asp.net-mvc - 使用自定义 ASP.NET MVC IValueProvider，而不进行全局设置？

Question

我希望能够从 cookie 中获取键/值并使用它来绑定(bind)模型。

我相信 DefaultModelBinder 开箱即用，而不是构建自定义 ModelBinder，并且选择值来自何处的最佳方法是设置它使用的 IValueProvider。

为此，我不想创建自定义 ValueProviderFactory 并将其绑定(bind)到全局，因为我只希望此 ValueProvider 用于特定的操作方法。

我已经建立了一个执行此操作的属性:

/// <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);
    }
}

不幸的是，ModelBinder 及其 IValueProvider 是在 OnActionExecuting 之前设置的(为什么？？？？？？)。有没有其他人想出一种在不使用 ValueProviderFactory 的情况下将自定义 IValueProvider 注入(inject) DefaultModelBinder 的方法？

Answer 1

这是一种替代方法，可让您将 IValueProviders 指定为针对操作参数的属性。
这使得 IValueProviders 是 transient 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，但有一些调整。
它不是密封的，因此您可以根据需要更改创建 IValueProvider 的方式。

这是一个简单的示例，它查看另一个字段，可能是隐藏或加密的字段，然后获取数据并将其放入另一个属性中。

这是模型，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，我的提供者明确知道我的模型，但不一定是这种情况。

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;
    }
}

然后是把这一切联系在一起的 Action :

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

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