使用 Autofac 将服务注入基类

Question

TL;DR：当两个自定义 ModelBinder 实现都依赖 Autofac 向其中注入（公共）依赖项时，如何将两个自定义 ModelBinder 实现共享的逻辑合并到单个基类中？

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在查看我正在处理的 ASP.NET MVC 项目中的一些代码时，我意识到我有两个自定义模型绑定程序，它们本质上执行相同的操作。它们都继承自 DefaultModelBinder，并且都使用注入到其构造函数中的 IEncodingService 对两个单独的视图模型类上的单个属性进行编码。

public class ResetQuestionAndAnswerViewModelBinder : DefaultModelBinder {
    public ResetQuestionAndAnswerViewModelBinder(IEncodingService encodingService) {
        encoder = encodingService;
    }

    private readonly IEncodingService encoder;

    public override object BindModel(ControllerContext controllerContext,
                                     ModelBindingContext bindingContext) {
        var model = base.BindModel(controllerContext, bindingContext) as ResetQuestionAndAnswerViewModel;

        if (model != null) {
            var answer = bindingContext.ValueProvider.GetValue("Answer");

            if ((answer != null) && !(answer.AttemptedValue.IsNullOrEmpty())) {
                model.Answer = encoder.Encode(answer.AttemptedValue);
            }
        }

        return model;
    }
}

public class ConfirmIdentityViewModelBinder : DefaultModelBinder {
    public ConfirmIdentityViewModelBinder(IEncodingService encodingService) {
        encoder = encodingService;
    }

    private readonly IEncodingService encoder;

    public override object BindModel(ControllerContext controllerContext,
                                     ModelBindingContext bindingContext) {
        var model = base.BindModel(controllerContext, bindingContext) as ConfirmIdentityViewModel;

        if (model != null) {
            var secretKey = bindingContext.ValueProvider.GetValue("SecretKey");

            if ((secretKey != null) && !(secretKey.AttemptedValue.IsNullOrEmpty())) {
                model.SecretKeyHash = encoder.Encode(secretKey.AttemptedValue);
            }
        }

        return model;
    }
}

我为这两个类编写了一个通用基类来继承：

public class EncodedPropertyModelBinder<TViewModel> : DefaultModelBinder 
    where TViewModel : class {

    public EncodedPropertyModelBinder(IEncodingService encodingService,
                                      string propertyName) {
        encoder = encodingService;
        property = propertyName;
    }

    private readonly IEncodingService encoder;
    private readonly string property;

    public override object BindModel(ControllerContext controllerContext,
                                     ModelBindingContext bindingContext) {
        var model = base.BindModel(controllerContext, bindingContext) as TViewModel;

        if (model != null) {
            var value = bindingContext.ValueProvider.GetValue(property);

            if ((value != null) && !(value.AttemptedValue.IsNullOrEmpty())) {
                var encodedValue = encoder.Encode(value.AttemptedValue);

                var propertyInfo = model.GetType().GetProperty(property);
                propertyInfo.SetValue(model, encodedValue, null);
            }
        }

        return model;
    }
}

使用 Autofac，我如何将 IEncodingService 注入基类构造函数，同时强制派生类提供要编码的属性名称？

Answer 1

实际上，我的处理方法略有不同，倾向于组合而不是继承。这意味着我将封装属性操作的细节，并将不同的实现传递给单个模型绑定器。

首先，定义一个表示绑定单个属性的接口：

public interface IPropertyBinder
{
    void SetPropertyValue(object model, ModelBindingContext context);
}

然后，使用来自 EncodedPropertyModelBinder 的参数实现它：

public sealed class PropertyBinder : IPropertyBinder
{
    private readonly IEncodingService _encodingService;
    private readonly string _propertyName;

    public PropertyBinder(IEncodingService encodingService, string propertyName)
    {
        _encodingService = encodingService;
        _propertyName = propertyName;
    }

    public void SetPropertyValue(object model, ModelBindingContext bindingContext)
    {
        var value = bindingContext.ValueProvider.GetValue(_propertyName);

        if(value != null && !value.AttemptedValue.IsNullOrEmpty())
        {
            var encodedValue = _encodingService.Encode(value.AttemptedValue);

            var property = model.GetType().GetProperty(_propertyName);

            property.SetValue(model, encodedValue, null);
        }
    }
}

接下来，使用新接口实现 EncodedPropertyModelBinder：

public class EncodedPropertyModelBinder : DefaultModelBinder
{
    private readonly IPropertyBinder _propertyBinder;

    public EncodedPropertyModelBinder(IPropertyBinder propertyBinder)
    {
        _propertyBinder = propertyBinder;
    }

    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var model = base.BindModel(controllerContext, bindingContext);

        if(model != null)
        {
            _propertyBinder.SetPropertyValue(model, bindingContext);
        }

        return model;
    }
}

最后，注册两个使用 Autofac 命名实例的视图模型版本，传入 PropertyBinder 的不同配置：

builder.
    Register(c => new EncodedPropertyModelBinder(new PropertyBinder(c.Resolve<IEncodingService>(), "Answer")))
    .Named<EncodedPropertyModelBinder>("AnswerBinder");

builder.
    Register(c => new EncodedPropertyModelBinder(new PropertyBinder(c.Resolve<IEncodingService>(), "SecretKey")))
    .Named<EncodedPropertyModelBinder>("SecretKeyBinder");