How deeply does .NET MAUI in Action cover DelegatingHandler?

Explains inheritance, SendAsync, request modification, dependency-injection registration, named clients, and handler chaining.

DelegatingHandler

As explained in .NET MAUI in Action

A delegating handler is an HTTP message handler that can inspect or modify a request or response before passing it to another handler.

A DelegatingHandler inspects or modifies HTTP requests before passing them to another handler. Attach one to an HttpClient to apply changes automatically instead of repeating them at every API call. section 8.3.2

Use a delegating handler to apply authentication and other request policies consistently:

Inherit from DelegatingHandler and override SendAsync. section 8.3.2
Modify the HttpRequestMessage, such as by adding an access-token header, then call the base method. section 8.3.2
Register the handler and attach it to a named HttpClient through IHttpClientFactory. section 8.3.3
Chain multiple handlers with AddHttpMessageHandler when separate request modifications or a controlled processing order are useful. section 8.3.3

Automatically adding an access token

An AuthHandler can read a stored access token, add it to each request, and pass the request onward. After successful login, assign loginResult.AccessToken to AuthHandler.AuthToken so later authenticated requests contain the token. section 8.3.2

How .NET MAUI in Action covers it

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Also explained in

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ASP.NET Core in Action, 3eDelegatingHandler is a .NET HttpMessageHandler base class that forwards processing to an inner handler while allowing additional behavior.

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Related concepts

AddHttpMessageHandlerused by · AddHttpMessageHandler is an IHttpClientBuilder extension method that adds a delegating handler type to an HttpClient handler pipeline.
custom HttpMessageHandlerincludes · A custom HttpMessageHandler is an application-defined HTTP pipeline component that modifies or observes requests and responses.
HttpMessageHandlerkind of · HttpMessageHandler is an abstract .NET component that processes HTTP request and response messages within an HttpClient handler chain.
HTTP clientuses · An HTTP client is software or an API component that sends HTTP requests and receives and processes HTTP responses.
single responsibility principleimplements · The single responsibility principle is a software design principle that gives a component one focused responsibility and one primary reason to change.

This explainer was generated by Manning's knowledge graph from the text of .NET MAUI in Action. The section links point to the parts of the book it draws on.