对 CustomFormatter 的依赖注入答案

【问题标题】：Dependency Injection to CustomFormatter对 CustomFormatter 的依赖注入
【发布时间】：2017-04-20 19:06:12
【问题描述】：

我在 webapi 中使用 ninject 作为依赖注入器。我所有的构造函数注入都对我的控制器工作正常。

我有自定义媒体类型格式化程序，当用户请求“应用程序/pdf”时，它会返回 pdf

这里我需要在创建 pdf 后更新数据。所以在这里我需要调用我的业务类来更新数据。

MyCustomFormatter 代码：

public class PdfMediaTypeFormatter : MediaTypeFormatter
{
    private readonly string mediaType = "application/pdf";
    Func<Type, bool> typeisIPdf = (type) => typeof(IPdf).IsAssignableFrom(type);
    Func<Type, bool> typeisIPdfCollection = (type) => typeof(IEnumerable<IPdf>).
    IsAssignableFrom(type);

    public PdfMediaTypeFormatter()
    {
        SupportedMediaTypes.Add(new MediaTypeHeaderValue(mediaType));
        MediaTypeMappings.Add(new UriPathExtensionMapping("pdf", new MediaTypeHeaderValue(mediaType)));
    }

    public override bool CanReadType(Type type)
    {
        return false;
    }

    public override bool CanWriteType(Type type)
    {
        return typeisIPdf(type) || typeisIPdfCollection(type);
    }

    public async override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
    {
        var pdfData= new SamplePdf();

        var memoryStream = report.Create(value);

        var bytes = memoryStream.ToArray();
        await writeStream.WriteAsync(bytes, 0, bytes.Length);
    }
}

我的 SamplePdf 类代码：

public class SamplePdf
{
    private readonly IBusinessLogic _logic;
    public MemoryStream Create(object model)
    {
       //Pdf generation code
       // here i need to call data update
       //_logic.update(model);
    }
}

我需要在我的商务舱中注入_logic 字段。我已经在下面的 ninject 配置中映射了相同的内容；

kernel.Bind<IBusinessLogic>().To<MyBusinessLogic>().InRequestScope();

如何将这个注入我的班级？

【问题讨论】：

是什么阻止您将其注入格式化程序？
格式化程序是无参数的。如果我在那里包含注入，我们将如何更改 webapi 配置中的代码。我的意思是自定义格式化程序注册码

标签： c# asp.net-web-api dependency-injection ninject

【解决方案1】：

根据提供的示例做出以下假设。

public class PdfMediaTypeFormatter : MediaTypeFormatter {
    private readonly string mediaType = "application/pdf";
    Func<Type, bool> typeisIPdf = (type) => typeof(IPdf).IsAssignableFrom(type);
    Func<Type, bool> typeisIPdfCollection = (type) => typeof(IEnumerable<IPdf>).
    IsAssignableFrom(type);
    private readonly IPdfFactory report;

    public PdfMediaTypeFormatter(IPdfFactory report) {
        SupportedMediaTypes.Add(new MediaTypeHeaderValue(mediaType));
        MediaTypeMappings.Add(new UriPathExtensionMapping("pdf", new MediaTypeHeaderValue(mediaType)));

        this.report = report;
    }

    public override bool CanReadType(Type type) {
        return false;
    }

    public override bool CanWriteType(Type type) {
        return typeisIPdf(type) || typeisIPdfCollection(type);
    }

    public async override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext) {

        var memoryStream = report.Create(value);

        var bytes = memoryStream.ToArray();

        await writeStream.WriteAsync(bytes, 0, bytes.Length);
    }
}

public interface IPdfFactory {
    MemoryStream Create(object model);
}

public class PdfFactory : IPdfFactory {
    private readonly IBusinessLogic _logic;

    public PdfFactory(IBusinessLogic logic) {
        this._logic = logic;
    }

    public MemoryStream Create(object model) {
        var stream = new MemoryStream();
        //...Pdf generation code

        //call data update
        _logic.update(model);

        return stream;
    }
}

注册会使用 DI 容器来解析格式化程序

public static class WebApiConfig {

    public static void Register(HttpConfiguration config) {
        //...DI configuration

        var formatter = (PdfMediaTypeFormatter)config.DependencyResolver.GetService(typeof(PdfMediaTypeFormatter));

        config.Formatters.Add(formatter);
    }
}

假设

kernel.Bind<IBusinessLogic>().To<MyBusinessLogic>();
kernel.Bind<IPdfFactory>().To<PdfFactory>();
kernel.Bind<PdfMediaTypeFormatter>().ToSelf();

参考Media Formatters in ASP.NET Web API 2

【讨论】：