是否可以使用可用于模型绑定的非公共无参数构造函数?

问题描述

我有一个以下的POCO课程.我不希望无参数构造函数是公开的.

I have a following POCO class. I don not want the parameterless constructor to be public.

public class FileDownloadRequest
    {
       //public FileDownloadRequest() { }
        public FileDownloadRequest(int fileId, RepositoryFolderTypes fileType) //RepositoryFolderTypes is an enum, not a class
        {
            this.FileId = fileId;
            this.FileType = fileType;
        }
        public int FileId { get; set; }
        public RepositoryFolderTypes FileType { get; set; } //an enum
    }

当我尝试对以下控制器操作执行https://10.27.8.6/Files/DownloadFile?fileId=1&folderType=SRC请求时，收到一条错误消息，指出该对象不存在无参数构造函数.

When I am trying a https://10.27.8.6/Files/DownloadFile?fileId=1&folderType=SRC request to the following controller action, I get an error saying that no parameterless constructor exists for this object.

[HttpGet]
public async Task<HttpResponseMessage> DownloadFile([FromUri] FileDownloadRequest request)
{
}

是否可以有一个非公共的构造函数，还是绝对需要一个公共的构造函数?

Is it possible to have a non-public constructor, or is a public one absolutely required?

推荐答案

是的，您可以使用任何喜欢的构造函数，但随后您必须自己绑定模型.问题出在DefaultModelBinder.CreateModel中，它使用无参数公共构造函数.

Yes, you can use any constructor you like, but you will have to do the model binding yourself then. The problem is in DefaultModelBinder.CreateModel, which uses a parameterless public constructor.

您必须覆盖默认的模型活页夹并创建自己的活页夹.如果那是值得的，那么时间取决于您.

You have to override the default model binder and create your own. If that is worth the time is up to you.

采取的步骤:

• 覆盖CreateModel;
• 检查modelType是否存在一些通用约束，您需要使用哪些参数调用构造函数并使用参数；
• 致电 Activator.CreateInstance(Type, Object[]) 与参数.您可以从bindingContext;
获取它们的值
• 通过ModelBinder属性或全局注册模型绑定器.

• Override CreateModel;
• Check the modelType for some generic constraint which models you need to call the constructor with parameters on;
• Call Activator.CreateInstance(Type, Object[]) with the parameters. You could obtain their values from the bindingContext;
• Register the model binder, either through the ModelBinder attribute, or globally.

在此处详细了解自定义绑定.

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