What is the reason of casting to IDisposable before calling Dispose() ?
public interface ITransaction : IDisposable
{}
.
.
.
//in some other class:
public void EndTransaction(ITransaction transaction)
{
if (transaction != null)
{
(transaction as IDisposable).Dispose();
// is the following code wrong? transaction.Dispose()
transaction = null;
}
}
This is one of the concrete implementation of ITransaction:
public class NHibernateTransaction : ITransaction
{
public NHibernateTransaction(NHibernate.ITransaction transaction)
{
this.Transaction = transaction;
}
protected NHibernate.ITransaction Transaction { get; private set; }
public void Dispose()
{
if ( this.Transaction != null )
{
(this.Transaction as IDisposable).Dispose(); // this is NHibernate ITransaction object
this.Transaction = null;
}
}
}
I have seen that code snippet many times in an open source implementation of the repository pattern and I cannot seem to understand the reason behind the cast. Directly calling transaction.Dispose() inside the if clause should work just fine. Did I miss something?
The original code can be found here:
NHibernateTransaction.cs
Since ITransaction inherits from IDisposable, it is possible that the implementer has implemented IDisposable as an explicit interface implementation, in which case the cast is required in order to access the implemented members.
In such a case, casting ensures that the call will call the IDisposable.Dispose method. The cast is done to cover all bases.
If ITransaction doesn't inherit from IDisposable, but the implementer does, a cast is needed for Dispose to be callable. Such a case may fail (throwing an exception) if the implementer does not implement IDisposable.
When calling Dipose() on an interface deriving from IDisposable, there is no difference.
There could be a difference when calling Dispose() on a class implementing IDisposable, because the method Dispose() may be implemented explicitly.
I don't do this often but I whacked my whole original answer as I understand what Oded is trying to say now. Their intent is to solve this problem:
namespace StackOverflow7051864
{
using System;
public interface ITransaction : IDisposable {}
public interface ITryToConfuseDispose
{
void Dispose();
}
public class Transaction : ITransaction, ITryToConfuseDispose
{
void IDisposable.Dispose()
{
Console.WriteLine("Happy");
}
void ITryToConfuseDispose.Dispose()
{
Console.WriteLine("Confused");
}
}
class Program
{
static void Main(string[] args)
{
EndTransaction(new Transaction());
}
public static void EndTransaction(ITransaction transaction)
{
(transaction as IDisposable).Dispose();
transaction.Dispose();
}
}
}
What does 'transaction.Dispose()' invoke? It invokes IDisposable.Dispose()
The problem though, is that since the contract into EndTransaction is ITransaction, it will always invoke the IDisposable version.
Related
I have following piece of C# code
iSomeObject.MyPoint(SomeConstants.cpU, 2,
myInterface.MySystem.MyCustomType == OtherConstants.cpProjected ? Constants.cpU : Constants.cpT,
1, ref t1, ref t2, ref t3);
When I ran my proprietary analysis tool it says that myInterface.MySystem is causing a resource leak.
class MyClass:MyInterface,IDisposable
{}
MyInterface myInterface = new MyClass();
And I'm explicitly disposing off instance myInstance by casting it back to IDisposable and calling Dipose() method on it.
Now MySystem properties' get method is invoked on myInterface which(MySystem) is of type IExampleInterface which is further implemented like the following code:
class ExampleClass:IExampleClass,IDisposable
{}
I'm not sure whether calling a Dipose() method on myInterface will also dispose off resource created by MySystem or do I need to explicitly call Dispose() method on it as well. But all is happening inside IF statement condition and I'm not sure how to handle this situation and make my code dispose off all disposable objects in other words I'm not sure about the C# syntax in this case and how to deal with dispoal concept in such a scenario.
Any suggestion will be appreciated.
If MySystem is an IDisposable object then your class should dispose of that object in it's implementation of Dispose.
Otherwise fix your static analysis tool.
I would say you should put the disposal at the layer of code that's aware that you have a MyClass.
using(var iSomeObject = new MyClass(...)) {
// do something
iSomeObject.MyPoint(SomeConstants.cpU, 2,
myInterface.MySystem.MyCustomType == OtherConstants.cpProjected ? Constants.cpU : Constants.cpT,
1, ref t1, ref t2, ref t3);
}
I am not sure what you mean by the if statement. If you use disposable instances in a method / property / constructor (whatever) and they are not scoped as instance members to the class they should be disposed of immediately after use.
If you have members in the class that implement IDisposable then your class should also implement IDisposable and the Dispose should be called as soon as an instance of your class is no longer needed (just like anything else that implements IDisposable).
Also always use a try/finally or using block when interacting with instances that implement IDisposable.
Finally see this write up from Microsoft for complete details and best practices for using IDisposable.
public interface IExampleInterface { void DoSomething();}
public class ExampleClass : IExampleInterface, IDisposable {
private bool _switch = true;
public void DoSomething() {
// lets use something disposable
if(_switch) { // is this what you mean by in an if statement??
var stream = new System.IO.MemoryStream();
try {
// do something with stream
} finally {
stream.Dispose(); // call dispose!
}
}
}
private System.IO.FileStream fs; // class level field
public void Dispose(){
// dispose of class fields here that implement IDisposable
if(fs != null)
fs.Dispose();
fs = null;
}
}
I work on a huge project in C# .NET 4.0. There is a custom class inherited from System.Net.Sockets.SocketAsyncEventArgs class. Something like the following:
public class SocketTaskArgs : SocketAsyncEventArgs
{
public SocketTaskArgs()
{
Completed += someEventhHandler;
}
public void CleanUp()
{
Completed -= someEventhHandler;
}
/*
There is a lot of code here that is unimportant at the moment.
*/
}
So, I wanted to move the content of CleanUp() method to Dispose(bool) method.
As first, I checked the source code of the base class - SocketAsyncEventArgs (using Go To Definition so that I saw metadata as source). I found out, this class implements IDisposable interface. Nice, I just need to override the Dispose(bool) method, don't I? (See IDisposable Interface on MSDN, the "IDisposable and the inheritance hierarchy" section, for more details). Nothing new for me... Unfortunately, the SocketAsyncEventArgs class is implemented as following:
public class SocketAsyncEventArgs : EventArgs, IDisposable
{
public void Dispose();
//some other stuff here
}
That means, there is no way how to override Dispose(bool) method, as it's implemented as private instead of protected... What is the reason for this?
Next, I read about SocketAsyncEventArgs.Dispose() method on MSDN. The funny thing is that, it contains the following section:
Notes to Inheritors
Dispose can be called multiple times by other
objects. When overriding Dispose(Boolean), be careful not to reference
objects that have been previously disposed of in an earlier call to
Dispose. For more information about how to implement Dispose(Boolean),
see Implementing a Dispose Method.
Wait... what?
When overriding Dispose(Boolean), ...
How am I supposed to override Dispose(Boolean)?
What is the recommended way to implement IDisposable interface in this case?
There doesn't seem to be anything stopping you from implementing IDisposable on your child class, take this example:
public class DisposableParent : IDisposable
{
public void Dispose()
{
Console.WriteLine("The parent was disposed.");
}
}
public class DisposableChild : DisposableParent, IDisposable
{
public new void Dispose()
{
base.Dispose();
Console.WriteLine("The child was disposed.");
}
}
public class Program
{
public static void Main()
{
using (DisposableChild c = new DisposableChild()) { }
Console.ReadKey(true);
}
}
Gives the following output:
The parent was disposed.
The child was disposed.
The compiler warns about hiding the dispose of the parent class in the child, so using the new operator gets rid of that warning, just make sure to call the base class Dispose from the child class (and implement it the right way).
The dispose for the child would become something like:
public class DisposableChild : DisposableParent, IDisposable
{
private bool _disposed = false;
public new void Dispose()
{
Dispose(true);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
if (!_disposed)
{
base.Dispose();
Console.WriteLine("The child was disposed.");
_disposed = true;
}
}
}
}
And yes, this still works if you do something like:
using (DisposableParent p = new DisposableChild())
{
}
But something like this can break it:
public class Program
{
public static void Main()
{
DisposableChild c = new DisposableChild();
DisposeOfIt(c);
Console.ReadKey(true);
}
public static void DisposeOfIt(DisposableParent p)
{
p.Dispose();
}
}
Only prints out that the parent was disposed. So if you used this method you would have to be careful about controlling the lifetime of your objects.
Given the following class which implements both Dispose and IDisposable.Dispose:
internal class DisposableClass : IDisposable
{
public void Dispose()
{
}
void IDisposable.Dispose()
{
}
}
When I make a call to DisposeableClass.Dispose (through an instance of the class), the public void Dispose is called:
DisposableClass newClass = new DisposableClass();
try
{
}
finally
{
newClass.Dispose();
}
If you change the try-finally to a using statement, IDisposable.Dispose is called.
using (DisposableClass newClass = new DisposableClass())
{
}
But NOT the IDisposable.Dispose which I defined.
The compiler translates the using-statement to ((IDisposable)newClass).Dispose(). The full methodname shows it to be from System.IDisposable.Dispose.
IL_0014: callvirt instance void [mscorlib]System.IDisposable::Dispose()
When will my custom implementation of IDisposable.Dispose be called?
Note that I am not using this actual implementation and I get that this should not be used. But I am still curious as to which implementation gets called when.
If I'd have a different implementation for each of the Dispose methods; which implementation would be called when?
Your approach to disposing is wrong. You should look at The Dispose Pattern to understand how to do this properly.
However... To answer your question how / why are they called...
Your public void Dispose() is being called when you say newClass.Dispose(); because it is the best "match" for what you have asked. By that (and without getting too complicated) it is because it is the highest in the hierarchy and therefore the one the compiler expects you to mean because it is the most specific. If you hadn't created your own it would have gone through hierarchy to find a Dispose method.
When you wrap with using the compiler produces code similar to this:
DisposableClass newClass = new DisposableClass();
try
{
}
finally
{
((IDisposable)newClass).Dispose();
}
This will therefore call the IDiposable version explicitly.
UPDATE
Full working sample below that will give this output:
Manually calling newClass.Dispose();
public void Dispose() being called.
Now wrapped in using...
void IDisposable.Dispose() being called.
Manually calling IDisposable.Dispose();
void IDisposable.Dispose() being called.
Full working code (paste this inside a console app and run):
using System;
namespace zPlayGround
{
class Program
{
static void Main()
{
Console.WriteLine("Manually calling newClass.Dispose();");
var newClass = new DisposableClass();
try
{
}
finally
{
newClass.Dispose();
}
Console.WriteLine("Now wrapped in using...");
using (var usingClass = new DisposableClass())
{
}
Console.WriteLine("Manually calling IDisposable.Dispose();");
var demoClass = new DisposableClass();
try
{
}
finally
{
((IDisposable)newClass).Dispose();
}
Console.ReadKey();
}
}
internal class DisposableClass : IDisposable
{
public void Dispose()
{
Console.WriteLine("public void Dispose() being called.\r\n");
}
void IDisposable.Dispose()
{
Console.WriteLine("void IDisposable.Dispose() being called.\r\n");
}
}
}
I've looked in SO about a question like this one, and even that I've found quite a few, any of those threw any light into this matter for me.
Let's assume I have this code:
public class SuperObject : IDisposable
{
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing) { }
}
Do I need the protected virtual void Dispose(bool) on SuperObject? Since there is really nothing to dispose there.
public interface ICustom : IDisposable { }
public class Custom : ICustom
{
public SuperObject Super { get; protected set; }
public Custom()
{
Super = new SuperObject();
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
public virtual void Dispose(bool disposing)
{
if (!disposing) return;
if (Super != null)
Super.Dispose();
}
}
public class Foo
{
public Foo()
{
using (var c = new Custom())
{
//do magic with c
}
}
}
Now what happens if I want/need/try to use Custom on a class like System.Web.Mvc.Controller which already implements and has implemented IDisposable?
public class Moo : Controller
{
Custom c;
public Moo()
{
c = new Custom();
}
// Use c throughout this class
}
How to properly dispose c in Moo?
The normal approach is to apply the standard IDisposable implementation - HOWEVER this is really only necessary if your class or some class that derives from it will use UNmanaged resources - this case is infact VERY rare (and when this case does apply it is better to wrap the unmanaged resource in its own class that has a full standard IDisposable implementation).
So assuming you are not dealing with UNmanaged resources (raw file handles, globally alloced memeory etc) and are only dealing with members that are disposable (i.e that have managed resources and implement IDisposable) then you can safely get a way with a mimimal implimentation of IDispose - that is:
Just have a single void Dispose() method. In that method just call dispose on dispoable members and then Dispose on the base class if its disposable. If you have a class hierachy its ok to make this Dispose virtual. There is no need to have a Dispose(bool) method. Nor is there any need to check if the object is disposed - because all your doing is calling dipsose on other objects and those implementation will do that check.
If you don't like the mimimal appraoch then apply the standard full implimentation (but it is not strictly necessary). I.e either do a standard implimentation because your a stickler for following the recommended approach OR do a simple minimal (but correct) implementation - but don't do something in between (i.e not standard, not simple or not correct)!
See this question for more details: Minimal IDispose implimenation for managed resources only
So in your case the following is the mimimal implimentation:
public class SuperObject : IDisposable {
public void Dispose() {
// Dispose code...just call dispose on dispoable members.
// If there are none then no need to implement IDisposable!
}
}
public interface ICustom : IDisposable { }
public class Custom : ICustom {
public SuperObject Super { get; protected set; }
public Custom() {
Super = new SuperObject();
}
public void Dispose() {
if (Super != null)
Super.Dispose();
}
}
public class Moo : Controller {
Custom c;
public Moo() {
c = new Custom();
}
public Dispose() {
if (c!=null)
c.Dispose()
base.Dispose();
}
}
Note that if Super object does not have any disposable resources then there is no point in implementing IDisposable and having a Dispose method. If Customs only disposable object is SuperObject then the same applies there, and again the same logic rocks through to Moo. Finally then if all the above applies and there are no other disposable objects around all you need really need is:
public class Moo : Controller {
Custom c;
public Moo() {
c = new Custom();
}
public Dispose() {
base.Dispose();
}
}
How to properly dispose c in Moo?
public class Moo : Controller
{
Custom c;
public Moo()
{
c = new Custom();
}
// Use c throughout this class
protected override Dispose(bool disposing)
{
base.Dispose(disposing);
if (disposing)
c.Dispose()
}
}
And that also answers your first question, Controller needs to make its Dispose(bool) method protected virtual or the above would not be possible.
But a few notes:
you don't have any isDisposed logic. It is a good idea to do the disposing only once, and you may want to trap usage-after-dispose.
omitting destructors (finalizers) is in itself a good idea but you now have the extra constraint that no derived class should own an unmanaged resource.
I have written the following class:
public class CoupleFrames
{
public CoupleFrames(ColorImageFrame cif, Bitmap df)
{
this.colorFrame = cif;
this.desktopFrame = df;
}
public ColorImageFrame colorFrame;
public Bitmap desktopFrame;
}
Now I'm using the following code for disposing the variables.
CoupleFrames cf = new CoupleFrames(frame1, frame2);
// some code...
cf.colorFrame.Dispose();
cf.desktopFrame.Dispose();
I'm not sure that this is the correct way. Someone can suggest me the correct way for disposing the entire object?
I'm not sure that this is the correct way. Someone can suggest me the correct way for disposing the entire object?
Sure - you should make CoupleFrames implement IDisposable, and its Dispose method should dispose of the objects it "owns". For example:
public sealed class CoupleFrames : IDisposable
{
private readonly ColorImageFrame colorFrame;
private readonly Bitmap desktopFrame;
public CoupleFrames(ColorImageFrame cif, Bitmap df)
{
// TODO: Argument validation, unless it's valid for these parameters
// to be null, in which case the Dispose method would need to be careful.
this.colorFrame = cif;
this.desktopFrame = df;
}
public void Dispose()
{
colorFrame.Dispose();
desktopFrame.Dispose();
}
}
A few points to note:
You should make sure it's clear that the CoupleFrame really "owns" these constituent objects. Disposal relies on a clear ownership model
If CoupleFrame isn't sealed (and can't be) you may need to go into a more complicated pattern with virtual methods and finalizers. It can get very complicated, and you should read the advice given here by Joe Duffy et al. If your class is sealed, a lot of that complexity goes away
Public fields are generally a bad idea (in terms of encapsulation), which is why I've made them private here. I've also made them readonly, as if they can be changed later you need to think about whether changing them should dispose of the previously-referenced object etc.
By making CoupleFrame implement IDisposable, you're basically telling all clients that they should dispose of any instance they own. If you're not happy with imposing that burden, you need to rethink the design a bit.
I would implement the Dispose pattern
public class CoupleFrames : IDisposable
{
public CoupleFrames(ColorImageFrame cif, Bitmap df)
{
this.colorFrame = cif;
this.desktopFrame = df;
}
public ColorImageFrame colorFrame;
public Bitmap desktopFrame;
private bool disposed;
public void Dispose()
{
Dispose(true);
GC.SupressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposed)
{
return;
}
if (disposing)
{
colorFrame.Dispose();
desktopFrame.Dispose();
}
disposed = true;
}
}
You can use the IDisposable interface.
public class CoupleFrames : IDisposable
{
....
public void Dispose()
{
// Your disposing code here
}
~CoupleFrames()
{
Dispose();
}
}
You can use the destructor to call the Dispose method since the object can sometimes be deleted by the GC.
Make CoupleFrames Implement the Idisposable Interface.
public class CoupleFrames : IDisposable
{
public CoupleFrames(ColorImageFrame cif, Bitmap df)
{
this.colorFrame = cif;
this.desktopFrame = df;
}
public ColorImageFrame colorFrame;
public Bitmap desktopFrame;
public void Dispose()
{
cf.colorFrame.Dispose();
cf.desktopFrame.Dispose();
}