asp.net-mvc-2 – ASP.NET MVC2 ModelMetadataProviders：重写Cr

AssociatedMetadataProvider派生自ModelMetadataProvider. CreateMetadata()在AssociatedMetadataProvider上声明.在您提供的链接中重写的DataAnnotationsMetadataProvider派生自AssociatedMetadataProvider.

MVC框架调用ModelMetadataProvider的GetMetadataForProperty()方法.

覆盖CreateMetadata()的原因是因为AssociatedModelMetadataProvider的默认GetMetadataForProperty()实现了对CreateMetadata()的调用.它看起来像这样：

public override ModelMetadata GetMetadataForProperty(Func<object> modelAccessor,Type containerType,string propertyName)
{
   if (containerType == null)
   {
       throw new ArgumentNullException("containerType");
   }
   if (string.IsNullOrEmpty(propertyName))
   {
       throw new ArgumentException(MvcResources.Common_NullOrEmpty,"propertyName");
   }
   PropertyDescriptor propertyDescriptor = this.GetTypeDescriptor(containerType).GetProperties().Find(propertyName,true);
   if (propertyDescriptor == null)
   {
       throw new ArgumentException(string.Format(CultureInfo.CurrentCulture,MvcResources.Common_PropertyNotFound,new object[] { containerType.FullName,propertyName   }));
   }
return this.GetMetadataForProperty(modelAccessor,containerType,propertyDescriptor);

}

protected virtual ModelMetadata GetMetadataForProperty(Func<object> modelAccessor,PropertyDescriptor propertyDescriptor) 
{
   IEnumerable<Attribute> attributes = this.FilterAttributes(containerType,propertyDescriptor,propertyDescriptor.Attributes.Cast<Attribute>());
   return this.CreateMetadata(attributes,modelAccessor,propertyDescriptor.PropertyType,propertyDescriptor.Name);
}

如果您正在将AssociatedMetadataProvider子类化为您提供的链接,则首选的可扩展性点是CreateMetadata方法,因为AssociatedMetadataProvider.GetMetadataForProperty()方法预先验证CreateMetadata()方法的合约.这样,您就知道如果您的CreateMetadata()方法中存在错误,您已经知道错误的来源在您的方法中,而不是在传递给它的参数中.

另外,这里是FilterAttributes()方法的源代码,以防你想知道：

protected virtual IEnumerable<Attribute> FilterAttributes(Type containerType,PropertyDescriptor propertyDescriptor,IEnumerable<Attribute> attributes)
{
if (!typeof(ViewPage).IsAssignableFrom(containerType) && !typeof(ViewUserControl).IsAssignableFrom(containerType))
    {
        return attributes;
    }
    return attributes.Where<Attribute>(delegate (Attribute a) {
        return !(a is ReadOnlyAttribute);
    });
}