MVC Model Binding 学习心得

protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            ValueProviderFactories.Factories.Insert(0, new CustomValueProviderFactory());
            ModelBinders.Binders.Add(typeof(AddressSummary), new AddressSummaryBinder()); 
            WebApiConfig.Register(GlobalConfiguration.Configuration);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
        }

CustomValueProvider:

 public class CountryValueProvider : IValueProvider
    {

        public bool ContainsPrefix(string prefix)
        {
            return prefix.ToLower().IndexOf("country") > -1;
        }
        
        public ValueProviderResult GetValue(string key)
        {
            if (ContainsPrefix(key))
            {
                return new ValueProviderResult("USA", "USA",
                    CultureInfo.InvariantCulture);
            }
            else
            {
                return null;
            }
        }
    } 

 public class CustomValueProviderFactory : ValueProviderFactory
    {

        public override IValueProvider GetValueProvider(ControllerContext
                controllerContext)
        {
            return new CountryValueProvider();
        }
    } 

Custom Model Binder

 public class AddressSummaryBinder : IModelBinder
    {
        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            AddressSummary model = (AddressSummary)bindingContext.Model
               ?? new AddressSummary();
            model.City = GetValue(bindingContext, "City");
            model.Country = GetValue(bindingContext, "Country");
            return model; 
        }

        private string GetValue(ModelBindingContext context, string name)
        {
            name = (context.ModelName == "" ? "" : context.ModelName + ".") + name;

            ValueProviderResult result = context.ValueProvider.GetValue(name);
            if (result == null || result.AttemptedValue == "")
            {
                return "<Not Specified>";
            }
            else
            {
                return (string)result.AttemptedValue;
            }
        } 
    }

这里要说明一下：context.ValueProvider.GetValue(name)里的ValueProvider是一个集合，调用GetValue的时候，实际上是尝试轮训所有的ValueProvider，如果第一次轮训的时候得到的值是null,那么下一次将会继续，直至轮训完所有的ValueProvider为止。

BindModel->ValueProviderCollection->ValueProvider->GetValue->UpdateModel