ASP.NET Core 依存関係の挿入（@inject）でSessionオブジェクトを使用する場合

ASP.NET Core 依存関係の挿入（@inject）で実行するメソッド内では、Userだけではなく、HttpContext、Sessionも取得できずnullになるので、ビューからパラメータで渡す。
下記は、ASP.NET Core 2.2 で、_Layout.cshtmlビューで実行する依存関係の挿入クラス（@inject UserSettingService UserSetting）に、セッションオブジェクト（HttpContext.Session）をパラメータで渡した例。

_Layout.cshtml


@using WebAppTest.Common
@using WebAppTest.Services
@using Microsoft.AspNetCore.Http
@inject UserSettingService UserSetting
<!DOCTYPE html>
<html>
<head>
    <meta charset=”utf-8″ />
    <meta name=”viewport” content=”width=device-width, initial-scale=1.0″ />
    <title>Test</title>
    <environment include=”Development”>
        <link rel=”stylesheet” href=”~/lib/bootstrap/dist/css/bootstrap.css” />
    </environment>
    <environment exclude=”Development”>
        <link rel=”stylesheet” href=”https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css”
              asp-fallback-href=”~/lib/bootstrap/dist/css/bootstrap.min.css”
              asp-fallback-test-class=”sr-only” asp-fallback-test-property=”position” asp-fallback-test-value=”absolute”
              crossorigin=”anonymous”
              integrity=”sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T” />
    </environment>
    @if (UserSetting.BackgroundColor(User, Context.Session) == BackgroundColor.White)
    {
        <link id=”cssfile” rel=”stylesheet” href=”~/css/site.css” />
    }
    else
    {
        <link id=”cssfile” rel=”stylesheet” href=”~/css/site-black.css” />
    }
</head>

@using WebAppTest.Common

@using WebAppTest.Services

@using Microsoft.AspNetCore.Http

@inject UserSettingService UserSetting

<!DOCTYPE html>

<html>

<head>

</environment>

asp-fallback-href=”~/lib/bootstrap/dist/css/bootstrap.min.css”

asp-fallback-test-class=”sr-only” asp-fallback-test-property=”position” asp-fallback-test-value=”absolute”

crossorigin=”anonymous”

integrity=”sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T” />

</environment>

@if (UserSetting.BackgroundColor(User, Context.Session) == BackgroundColor.White)

{

}

else

{

}

</head>