模型绑定 - 输入外部装配体

Question

我在程序集中有一个类型，它没有被核心库引用，但被 Web 应用程序引用。例如

namespace MyApp.Models {
    public class LatestPosts {
        public int NumPosts { get; set; }
    }
}

现在我在核心库中有以下代码：

[HttpPost, ValidateAntiForgeryToken]
public ActionResult NewWidget(FormCollection collection) {
    var activator = Activator.CreateInstance("AssemblyName", "MyApp.Models.LatestPosts");
    var latestPosts = activator.Unwrap();

    // Try and update the model
    TryUpdateModel(latestPosts);
}

代码很容易解释，但 latestPosts.NumPosts 属性永远不会更新，即使该值存在于表单集合中。

如果有人能帮助解释为什么这不起作用以及是否有替代方法，我将不胜感激。

谢谢

Answer 1

您的问题与该类型在另一个程序集中或您使用Activator.Create 动态创建它的事实无关。以下代码以非常简化的方式说明了这个问题：

[HttpPost, ValidateAntiForgeryToken]
public ActionResult NewWidget(FormCollection collection) 
{
    // notice the type of the latestPosts variable -> object
    object latestPosts = new MyApp.Models.LatestPosts();

    TryUpdateModel(latestPosts);

    // latestPosts.NumPosts = 0 at this stage no matter whether you had a parameter
    // called NumPosts in your request with a different value or not
    ...
}

问题源于Controller.TryUpdateModel<TModel> 使用typeof(TModel) 而不是model.GetType() 来确定模型类型，如this connect issue 中所述（已关闭原因：by design）。

解决方法是滚动您的自定义 TryUpdateModel 方法，该方法的行为将与您预期的一样：

protected internal bool MyTryUpdateModel<TModel>(TModel model, string prefix, string[] includeProperties, string[] excludeProperties, IValueProvider valueProvider) where TModel : class
{
    if (model == null)
    {
        throw new ArgumentNullException("model");
    }
    if (valueProvider == null)
    {
        throw new ArgumentNullException("valueProvider");
    }

    Predicate<string> propertyFilter = propertyName => new BindAttribute().IsPropertyAllowed(propertyName);
    IModelBinder binder = Binders.GetBinder(typeof(TModel));

    ModelBindingContext bindingContext = new ModelBindingContext()
    {
        // in the original method you have:
        // ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, typeof(TModel)),
        ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(() => model, model.GetType()),
        ModelName = prefix,
        ModelState = ModelState,
        PropertyFilter = propertyFilter,
        ValueProvider = valueProvider
    };
    binder.BindModel(ControllerContext, bindingContext);
    return ModelState.IsValid;
}

然后：

[HttpPost, ValidateAntiForgeryToken]
public ActionResult NewWidget(FormCollection collection) 
{
    object latestPosts = new MyApp.Models.LatestPosts();

    MyTryUpdateModel(latestPosts, null, null, null, ValueProvider);

    // latestPosts.NumPosts will be correctly bound now
    ...
}