获取特定实例的ModelMetadata

Question

我正在尝试获取与数组中的实例相关联的元数据。我已经定义了一个在我的视图中调用的HtmlHelper扩展。我正在尝试创建一个帮助器来显示模型及其错误消息的列表。

@model Domain.Models.Customer
@this.Html.Example(m => m.Orders)

下面是我的帮助器的实现

public static class HtmlHelperExtensions
{
    public static IHtmlString Example<TModel, TInstance>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TInstance[]>> expression)
    {
        var instanceProvider = expression.Compile();
        var instances = instanceProvider.Invoke(helper.ViewData.Model);

        if(instances != null)
        {
            var properties = typeof (TInstance).GetProperties();
            for(var i = 0; i < instances.Length; i++)
            {
                var instanceExpression = Expression.ArrayIndex(expression.Body, Expression.Constant(i));

                foreach(var info in properties)
                {
                    var propertyExpression = Expression.Property(instanceExpression, info);

                    // How can i get access to the ModelMetadata
                    ModelMetadata.FromStringExpression(propertyExpression.ToString(), helper.ViewData);

                    // To get the model state we need the following...
                    var text = ExpressionHelper.GetExpressionText(Expression.Lambda(propertyExpression));
                    var fieldName = helper.ViewData.TemplateInfo.GetFullHtmlFieldName(text);

                    ModelState state;
                    if(helper.ViewData.ModelState.TryGetValue(fieldName, out state))
                    {
                        // Output errors....
                    }
                }

            }
        }

        return MvcHtmlString.Empty;
    }
}

使用以下域类

public class Customer
{
    public Order[] Orders { get; set; }
}

public class Order
{
    public string Description { get; set; }
}

Answer 1

据我所知，它不在那里！

ModelMetadata将用于模型的属性，在本例中是数组本身的属性，而不是数组内的元素。

因此，如果数组中的元素需要ModelMetadata，则需要创建Custom Model元数据提供程序，该提供程序将获取所需的属性并将它们添加到ModelMetadata中，示例指南代码片段

public class ArrayMetadataProvider : DataAnnotationsModelMetadataProvider
{

    protected override ModelMetadata CreateMetadata(IEnumerable<Attribute> attributes, Type containerType,
                                                    Func<object> modelAccessor, Type modelType, string propertyName)
    {
        var metadata = base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);

        // Add your metadata here

        return metadata;
    }

}

然后，您需要按如下方式注册此提供程序：

 protected void Application_Start()
    {

        ModelMetadataProviders.Current = new ArrayMetadataProvider();

    }