C# using的用法

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
//为命名空间定义别名 "ElseName"
using ElseName = This.Is.Very.Very.Long.NamespaceName;
//为类定义定义别名
using ElseCName = This.Is.Very.Very.Long.NamespaceName.ThisIsVeryVeryLongClassName;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //通过别名实例化对象   ::是命名空间别名的修饰符
        ElseName::NamespaceExample NSEx = new ElseName::NamespaceExample();
        //通过别名实例化对象
        ElseCName CN = new ElseCName();
        Response.Write("命名空间：" + NSEx.GetNamespace() + "；类名：" + CN.GetClassName());
    }
}

namespace This.Is.Very.Very.Long.NamespaceName
{
    class NamespaceExample
    {
        public string GetNamespace()
        {
            return this.GetType().Namespace;
        }
    }

    class ThisIsVeryVeryLongClassName
    {
        public string GetClassName()
        {
            return System.Reflection.MethodBase.GetCurrentMethod().DeclaringType.FullName;
        }
    }
}

string str = "LittleBai";
//创建写入字符串
Byte[] bytesToWrite = Encoding.Default.GetBytes(str); ;
//创建文件
using (FileStream fs = new FileStream("test.txt", FileMode.Create))
{
    //将字符串写入文件
    fs.Write(bytesToWrite, 0, bytesToWrite.Length);
}