Types that own disposable fields should be disposable

A class declares and implements an instance field that is a System.IDisposable type and the class does not implement IDisposable.

A class implements the IDisposable interface to dispose of unmanaged resources that it owns. An instance field that is an IDisposable type indicates that the field owns an unmanaged resource. A class that declares an IDisposable field indirectly owns an unmanaged resource and should implement the IDisposable interface. If the class does not directly own any unmanaged resources, it should not implement a finalizer.

To fix a violation of this rule, implement IDisposable and from the System.IDisposable.Dispose method call the field's Dispose method.

Do not exclude a warning from this rule.

The following example shows a class that violates the rule and a class that satisfies the rule by implementing IDisposable. The class does implement a finalizer because it does not directly own any unmanaged resources.

Imports System
Imports System.IO
  
Namespace DesignLibrary

   ' This class violates the rule.
   Public Class NoDisposeMethod
   
      Dim newFile As FileStream

      Sub New()
         newFile = New FileStream("c:\temp.txt", FileMode.Open)
      End Sub

   End Class

   ' This class satisfies the rule.
   Public Class HasDisposeMethod 
      Implements IDisposable
   
      Dim newFile As FileStream

      Sub New()
         newFile = New FileStream("c:\temp.txt", FileMode.Open)
      End Sub

      Overloads Protected Overridable Sub Dispose(disposing As Boolean)

         If disposing Then
            ' dispose managed resources
            newFile.Close()
         End If

         ' free native resources

      End Sub 'Dispose
     
      
      Overloads Public Sub Dispose() Implements IDisposable.Dispose

         Dispose(True)
         GC.SuppressFinalize(Me)

      End Sub 'Dispose
    
   End Class

End Namespace

using System;
using System.IO;
  
namespace DesignLibrary
{
   // This class violates the rule.
   public class NoDisposeMethod
   {
      FileStream newFile;

      public NoDisposeMethod()
      {
         newFile = new FileStream(@"c:\temp.txt", FileMode.Open);
      }
   }

   // This class satisfies the rule.
   public class HasDisposeMethod: IDisposable
   {
      FileStream newFile;

      public HasDisposeMethod()
      {
         newFile = new FileStream(@"c:\temp.txt", FileMode.Open);
      }

      protected virtual void Dispose(bool disposing)
      {
         if (disposing)
            {
               // dispose managed resources
               newFile.Close();
            }
          // free native resources
      }

      public void Dispose()
      {
         Dispose(true);
         GC.SuppressFinalize(this);
      }
   }
}

Disposable fields should be disposed

Disposable types should declare finalizer

Dispose methods should call base class dispose

Types that own native resources should be disposable