如何將運行時參數值轉換爲WebJobs函數和Simple Injector內的依賴項？

Question

我有一個WebJobs函數，它有一個方法/觸發器。它的一個參數的對應WebJobs儀表盤記錄：

public Task MyQueueHandler(TextWriter log) 

我怎麼能轉換或在容器中註冊該TextWriter log所以可以注入到我的另一個類的構造函數：

public MyLogger(TextWriter log) 

有沒有想辦法通過使用ExecutionContextScoping？

Answer 1

您可以在提供程序後面提取TextWriter，並將提供程序注入記錄器（因爲TextWriter明顯是運行時數據，應直接使用prevent injecting it into your components）。這允許您在調用MyQueueHandler時將此值設置到提供程序中。例如：

// Definition 
public interface ITextWriterProvider // by lack of a better name 
{ 
    TextWriter Current { get; } 
} 

// Used as dependency of MyLogger 
public MyLogger(ITextWriterProvider logProvider) 

// Implementation visible to your composition root 
public class TextWriterProvider : ITextWriterProvider 
{ 
    public TextWriter Current { get; set; } 
} 

// Registration 
container.Register<ITextWriterProvider, TextWriterProvider>(Lifestyle.Scoped); 
container.Register<TextWriterProvider>(Lifestyle.Scoped); 

// Wrap the start of the request in a scope and assign the log value to the scope. 
public Task MyQueueHandler(TextWriter log) 
{ 
    using (AsyncScopedLifestyle.BeginScope(container)) 
    { 
     container.GetInstance<TextWriterProvider>().Current = log; 

     // execute rest of request 
    } 
} 

這種設計的變化也可以使TextWriterProvider獨立的，並使其價值AsyncLocal，如下所示：

public class TextWriterProvider : ITextWriterProvider 
{ 
    private static readonly AsyncLocal<TextWriter> current = 
     new AsyncLocal<TextWriter>(); 

    public TextWriter Current 
    { 
     get => current.Value; 
     set => current.Value = value; 
    } 
} 

// Registration 
container.Register<ITextWriterProvider, TextWriterProvider>(Lifestyle.Singleton); 
container.Register<TextWriterProvider>(Lifestyle.Singleton); 

或者更簡單：

public class TextWriterProvider : ITextWriterProvider 
{ 
    public static readonly AsyncLocal<TextWriter> CurrentWriter = 
     new AsyncLocal<TextWriter>(); 

    public TextWriter Current => CurrentWriter.Value; 
} 

// Registration 
container.Register<ITextWriterProvider, TextWriterProvider>(Lifestyle.Singleton); 

// Assign the log to the CurrentWriter at the start of the request 
public Task MyQueueHandler(TextWriter log) 
{ 
    TextWriterProvider.CurrentWriter = log; 

    // execute rest of request 
} 

這些都是同一設計的所有變體，我們從構造函數中提取運行時數據並允許在之後解析它對象圖已經構建完成。

如果全部失敗，可以將此運行時值直接注入到對象圖中。請注意，我強烈反對此建議，但將其視爲最後的選擇：

// Part of your Composition Root 
public static AsyncLocal<TextWriter> Writer = new AsyncLocal<TextWriter>(); 

// Registration 
container.Register<ILogger>(() => new MyLogger(
    Writer ?? (container.IsVerifying ? new TextWriter() : null))); 

// Assign the log to the CurrentWriter at the start of the request 
public Task MyQueueHandler(TextWriter log) 
{ 
    CompositionRoot.CurrentWriter = log; 

    // execute rest of request 
}