Use of using keyword in C# (.Net) (Viewed - 4145 times)



There are three use of using keywords

  1. using directive to use to import namespace in C# class
  2. Create a using directive to use the types in a namespace withough having to specify that actual namespace (i.e. using directive creates an alias).
  3. To automatically close and dispose any object references implementing the IDisposable interface

A using directive does not give you access to any of the various namespaces that might be nested in the namespace that you specified.

A user defined namespace is referring to any namespace you have created in your code.

Example For 2nd Point:

// using keyword
using System;
using CSF = SomeMain.Resource.ForCSharp;  // alias 

namespace SomeMain.Resource
{
    public class MyClass
    {
        public static void Something()
        {
            //empty
        }
    }

    namespace ForCSharp
    {
        public class MyNestedClass
        {
            public static void MyMessage()
            {
                System.Console.WriteLine("CSharpFriends!");
            }
        
        }        
    
    }

}
public class TestUsing
{
    public static void Main()
    {
        CSF.MyNestedClass.MyMessage();
        
        // pauses output window
        Console.ReadLine();
    }
}


Example 3rd Point:

using (SqlConnection cn = new SqlConnection(connectionString))
{
      // do something
}

is the same as:

SqlConnection cn = new SqlConnection(connectionString)
try
{
           // do something...
}
catch
{  }
finally
{
        cn.Dispose();
}



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