如何使用attributes向具有ASP.NET核心的附加值集合ModelMetadata添加项？

using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;

public class CustomMetadataAttribute : Attribute, IModelMetadataAdditionalValues
{
    public void Process(ModelMetadataEntry entry, string key)
    {
        // 添加自定义的元数据项到AdditionalValues字典中
        entry.AdditionalValues[key] = "Custom Value";
    }
}

public class MyModel
{
    [CustomMetadata]
    public string MyProperty { get; set; }
}

using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc()
            .AddMvcOptions(options =>
            {
                options.ModelMetadataDetailsProviders.Add(new CustomMetadataProvider());
            });
    }
}

using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;

public class CustomMetadataProvider : DefaultModelMetadataDetailsProvider
{
    public override void CreateMetadata(ModelMetadataCreationContext context)
    {
        base.CreateMetadata(context);

        var attributes = context.Attributes;
        var modelMetadata = context.Metadata;

        foreach (var attribute in attributes)
        {
            if (attribute is CustomMetadataAttribute customAttribute)
            {
                customAttribute.Process(modelMetadata, "CustomKey");
            }
        }
    }
}

var myModelMetadata = modelMetadataProvider.GetMetadataForType(typeof(MyModel));
var myPropertyMetadata = myModelMetadata.Properties.FirstOrDefault(p => p.PropertyName == "MyProperty");

if (myPropertyMetadata != null)
{
    if (myPropertyMetadata.AdditionalValues.TryGetValue("CustomKey", out var customValue))
    {
        // 使用自定义元数据项
        Console.WriteLine(customValue);
    }
}