Chapter62:IDisposableinterface

Section62.1:Inaclassthatcontainsonlymanagedresources

Managedresourcesareresourcesthattheruntime’sgarbagecollectorisawareandundercontrolof.Thereare manyclassesavailableintheBCL,forexample,suchasaSqlConnectionthatisawrapperclassforanunmanaged resource.TheseclassesalreadyimplementtheIDisposableinterface–it’suptoyourcodetocleanthemupwhen you are done.

It’snotnecessarytoimplementafinalizerifyourclassonlycontainsmanagedresources.

publicclassObjectWithManagedResourcesOnly:IDisposable

{

privateSqlConnectionsqlConnection=newSqlConnection();

publicvoidDispose()

{

sqlConnection.Dispose();

}

}

Section62.2:Inaclasswithmanagedandunmanaged resources

It’simportanttoletfinalizationignoremanagedresources.Thefinalizerrunsonanotherthread–it’spossiblethat themanagedobjectsdon’texistanymorebythetimethefinalizerruns.ImplementingaprotectedDispose(bool)methodisacommonpracticetoensuremanagedresourcesdonothavetheirDisposemethodcalledfroma finalizer.

publicclassManagedAndUnmanagedObject:IDisposable

{

privateSqlConnectionsqlConnection=newSqlConnection();

privateUnmanagedHandleunmanagedHandle=Win32.SomeUnmanagedResource();

privatebooldisposed;

publicvoidDispose()

{

Dispose(true);//clientcalleddispose

GC.SuppressFinalize(this);//telltheGCtonotexecutetheFinalizer

}

protectedvirtualvoidDispose(booldisposeManaged)

{

if(!disposed)

{

if(disposeManaged)

{

if(sqlConnection!=null)

{

sqlConnection.Dispose();

}

}

unmanagedHandle.Release();

disposed=true;

}

}

~ManagedAndUnmanagedObject()

{

Dispose(false);

}

}

Section62.3:IDisposable,Dispose

.NETFrameworkdefinesainterfacefortypesrequiringatear-downmethod:

publicinterfaceIDisposable

{

voidDispose();

}

Dispose()isprimarilyusedforcleaningupresources,likeunmanagedreferences.However,itcanalsobeusefulto forcethedisposingofotherresourceseventhoughtheyaremanaged.InsteadofwaitingfortheGCtoeventually alsocleanupyourdatabaseconnection,youcanmakesureit’sdoneinyourownDispose()implementation.

publicvoidDispose()

{

if(null!=this.CurrentDatabaseConnection)

{

this.CurrentDatabaseConnection.Dispose();

this.CurrentDatabaseConnection=null;

}

}

Whenyouneedtodirectlyaccessunmanagedresourcessuchasunmanagedpointersorwin32resources,createa class inheriting from SafeHandleand use that class’sconventions/tools to do so.

Section62.4:usingkeyword

WhenanobjectimplementstheIDisposableinterface,itcanbecreatedwithintheusingsyntax:

using(varfoo=newFoo())

{

//dofoostuff

}//whenitreachesherefoo.Dispose()willgetcalled

publicclassFoo:IDisposable

{

publicvoidDispose()

{

Console.WriteLine(“disposecalled”);

}

}

Viewdemo

usingissyntaticsugarforatry/finallyblock;theaboveusagewouldroughlytranslateinto:

{

varfoo=newFoo();

try

{

//dofoostuff

}

finally

{

if (foo!=null) ((IDisposable)foo).Dispose();

}

}

Section62.5:Inaninheritedclasswithmanagedresources

It’sfairlycommonthatyoumaycreateaclassthatimplementsIDisposable,andthenderiveclassesthatalso containmanagedresources.ItisrecommendededtomarktheDisposemethodwiththevirtualkeywordsothat clientshavetheabilitytocleanupanyresourcestheymayown.

publicclassParent:IDisposable

{

privateManagedResourceparentManagedResource=newManagedResource();

publicvirtualvoidDispose()

{

if(parentManagedResource!=null)

{

parentManagedResource.Dispose();

}

}

}

publicclassChild:Parent

{

privateManagedResourcechildManagedResource=newManagedResource();

publicoverridevoidDispose()

{

if(childManagedResource!=null)

{

childManagedResource.Dispose();

}

//cleanuptheparent’sresources

base.Dispose();

}

}