IDisposable และคำสั่ง using

เหตุผลที่ใช้ IDisposable และ using

ใช้งาน IDisposable

using System;

// Simple disposable that tracks whether it was cleaned up
public sealed class FakeConnection : IDisposable
{
  public bool IsOpen { get; private set; }

  public FakeConnection()
  {
    IsOpen = true;
    Console.WriteLine("Open");
  }

  public void Dispose()
  {
    if (IsOpen)
    {
      IsOpen = false;
      Console.WriteLine("Close");
    }
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    FakeConnection c = new FakeConnection();
    c.Dispose(); // manual cleanup
  }
}

รูปแบบ try/finally

using System;

public sealed class FakeConnection : IDisposable
{
  public void Dispose() { Console.WriteLine("Dispose called"); }
  public void Send(string msg) { Console.WriteLine("Send: " + msg); }
}

public class Program
{
  public static void Main(string[] args)
  {
    // Manual try/finally
    FakeConnection a = null;
    try
    {
      a = new FakeConnection();
      a.Send("A");
      throw new Exception("boom");
    }
    finally
    {
      if (a != null) a.Dispose(); // runs even on exception
    }

    // unreachable due to thrown exception in this demo
  }
}

ตัวอย่างคำสั่ง using

using System;

public sealed class FakeConnection : IDisposable
{
  public void Dispose() { Console.WriteLine("Dispose called"); }
  public void Work() { Console.WriteLine("Working"); }
}

public class Program
{
  public static void Main(string[] args)
  {
    try
    {
      using (FakeConnection c = new FakeConnection())
      {
        c.Work();
        throw new InvalidOperationException("oops");
      } // Dispose runs here automatically
    }
    catch (Exception)
    {
      Console.WriteLine("Handled");
    }
  }
}

I/O ด้วย using

using System;
using System.IO;

public class Program
{
  public static void Main(string[] args)
  {
    // Create a small temp file then read it
    string path = "demo.txt";
    File.WriteAllText(path, "hello");

    using (StreamReader r = new StreamReader(path))
    {
      string text = r.ReadToEnd();
      Console.WriteLine(text);
    } // r.Dispose() closes the file handle
  }
}

เคล็ดลับและข้อควรระวังเรื่อง using

การรับประกันของคำสั่ง using

ทบทวน