209 words (approximately 1 min)

Imports

using namespace; // Imports all classes from namespace.
using static namespace; // Imports only the static methods from namespace.
using static System.Console; // This allows you to use WriteLine() without having to call Console.WriteLine().
global using namespace;	// Allows importing namespace into one file but available to the whole project.

Console applications have these implicit using directives (auto imports):

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

Other auto imports can be found in /obj/Debug/net6.0/TopLevelProgram.GlobalUsings.g.cs.

Using Directive

using namespace;

Aliases

using SomeAlias = Really.Long.Nested.Namespace;

Global

The global modifier has the same effect as adding the same using directive to every source file in a project:

global using namespace;

Can also be added to project file instead:

<Using>namespace</Using>

Static

The static modifier imports only the static members and nested types from a namespace:

static using namespace;

Implicit Using Directives

Implicitly imports:

  • System
  • System.IO
  • System.Collections.Generic
  • System.Linq
  • System.Net.Http
  • System.Threading
  • System.Threading.Tasks

Disabling

To disable implicit imports, add this line to the project file:

<ImplicitUsings>disable</ImplicitUsings>

To use implicit imports but remove a specific one:

<ItemGroup>
	<Using Remove="System.Net.Http" />
</ItemGroup>

Using Statement

The using statement generates a finally statement that calls the Dispose() method on an object that implements IDisposable:

using (FileStream xmlFileStream = File.Create(file.xml)) { … }