use of “using” keyword in c# [duplicate]

Answer 1

Two uses:

• Using directives, e.g.

  using System;
  using System.IO;
  using WinForms = global::System.Windows.Forms;
  using WinButton = WinForms::Button;
  

  These are used to import namespaces (or create aliases for namespaces or types). These go at the top of the file, before any declarations.

• Using statements e.g.

  using (Stream input = File.OpenRead(filename))
  {
      ...
  }
  

  This can only be used with types that implement IDisposable, and is syntactic sugar for a try/finally block which calls Dispose in the finally block. This is used to simplify resource management.

Answer 2

There are two different uses of the using keyword in C#:

1. To declare implicit package scope, for example "using System;"
2. To cause the Dispose() method of an IDisposable object to be called.

In the latter case, using(myVar) {} is shorthand for:

IDisposable disposable = (IDisposable)myVar;
try
{
   // your code here
}
finally
{
   if (disposable != null)
      disposable.Dispose();
}

Answer 3

See:
using statement
using directive

Answer 4

"using" keyword can also be used to make type aliases. Here Item is an alias to Dictionary. This approach can save you some typing :)

For instance,

using Item = System.Collections.Generic.Dictionary<string, string>;
namespace Sample
{
    using Records = Dictionary<int, Item>;
    public class Controller
    {
      Records recordDictionary = new Records();
    }
}

Answer 5

Pretty sure there will be a duplicate of this one somewhere....however, in short the using keywords is used to specify the scope of the object you are creating. The object is disposed once it exits the using block i.e. Dispose is called automatically.

See using Statement (C#) for more details.

Answer 6

It gives you an easy way to cleanup resources after you are done with them. With the using construct, once you are done using the resources, they are freed automatically. It even cleans up the resources in the case of an exception.