packages/Microsoft.Extensions.Options.8.0.0/PACKAGE.md

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## About
`Microsoft.Extensions.Options` provides a strongly typed way of specifying and accessing settings using dependency injection and acts as a bridge between configuration, DI, and higher level libraries. This library is the glue for how an app developer uses DI to configure the behavior of a library like HttpClient Factory. This also enables user to get a strongly-typed view of their configuration.

Within this package, you'll find an options validation source generator that generates exceptionally efficient and optimized code for validating options.

## Key Features

* Offer the IValidateOptions interface for the validation of options, along with several generic ValidateOptions classes that implement this interface.
* OptionsBuilder to configure options.
* Provide extension methods for service collections and options builder to register options and validate options.
* Supply a set of generic ConfigureNamedOptions classes that implement the IConfigureNamedOptions interface for configuring named options.
* Provide a source generator that generates validation code for options.
* Options caching, managing and monitoring.

## How to Use

#### Options validation example

```C#
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllersWithViews();

// Load the configuration and validate it
builder.Services.AddOptions<MyConfigOptions>()
            .Bind(builder.Configuration.GetSection(MyConfigOptions.MyConfig))
            .ValidateDataAnnotations();
var app = builder.Build();


// Declare the option class to validate
public class MyConfigOptions
{
    public const string MyConfig = "MyConfig";

    [RegularExpression(@"^[a-zA-Z''-'\s]{1,40}$")]
    public string Key1 { get; set; }
    [Range(0, 1000,
        ErrorMessage = "Value for {0} must be between {1} and {2}.")]
    public int Key2 { get; set; }
    public int Key3 { get; set; }
}
```

#### Using IValidateOptions to validate options

```C#
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllersWithViews();

// Configuration to validate