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How to dispose object

How to dispose my object? I am doing it by this. Whats is wrong? The Obj.Dispose() function does not appear to be right.
class MainclassForm : Form, IDisposeable
{
public void createanddispose()
{
A obj = new A();
obj.dowork();
obj.Dispose();//does not appear as a function
}
}

You can better use the using statement. Something like
using (MyIDisposableObject obj = new MyIDisposableObject())
{
// object here
}
A good reference to check on MSDN: Avoiding Problems with the Using Statement
The C# "using" statement results in a call to Dispose(). This is the
same as Close(), which may throw exceptions when a network error
occurs. Because the call to Dispose() happens implicitly at the
closing brace of the "using" block, this source of exceptions is
likely to go unnoticed both by people writing the code and reading the
code. This represents a potential source of application errors.

To call Dispose() on an object, your class must be inherited from IDisposeable interface and have an implementation of it:
class A : IDisposable
{
public void Dispose()
{
GC.Collect();
}
}

There are a couple things wrong here, but I believe the root is that you might confusing IDisposable with a Garbage Collector.
IDisposable is an interface that the type A, in your example, may implement. It that were the case, you could be sure that any instance of A had the method Dispose() you're looking for. This is useful for things like Streams, where they need to be closed, but it's not useful for (just as an example) a ComplexNumber type that has no outstanding resources.
In these cases, your managed C# code will handle all the "disposal" that needs to happen. It will get rid of the memory that object is using. That feature comes for free (sort of), and you don't need (or want) to do anything to explicitly invoke it. That's the main difference between managed (C#, Java, etc.) and unmanaged (C++) code.
Essentially, if an object is using more than just memory (like an open file does), IDisposable will be useful. If it is just memory (like a Form, or DateTime, or a majority of other things), there's no need for it.
As for your specific code, you've applied IDisposable to the type that contains your functions. Just as you couldn't call this.AddMinutes(1) to get at DateTime's method, you can't get at this one.
If you do need the added functionality of implementing IDisposable, you'll have to do it on A. Applying IDisposable, like any other interface, to MainclassForm will tell the compiler that you have a Dispose() method on that class, which is true only because the Windows Forms object has one. If it didn't, this would throw a compiler error, and you'd have to add one.

Advantage of using IDisposable over performing actions in C# class finalizer

There are a lot of question discussing the "patterned" was of implementing and using IDisposable/Dispose, but what advantage does it have over having all the cleanup code in C# class finilizer?
Sure other classes can explicitly call Dispose earlier than the class instance is garbage collected and the finilizer is called. Is it the only one?

You have no guarantees about when or even if a Finalizer (destructor) will be called.
So in order to timely cleanup resources (Files, Db Connections) the Dispose pattern is essential.

The IDisposable is made to avoid destructors. The problem with destructors is that you never know when they are called, and objects with destructors are always the last to be cleaned up.
Using IDisposable you inform the user of you class that they should be using thwe using-method.
Eg:
using(MyClass myClass = new MyClass())
{
// Do something with MyClass.
}

using in defining object in c#

when we use using for defining an object?for example:
using (Login objLogin = new Login())
i know that we use when we want to clean the memory after using this object but i dont know when should we clean the memory.

The using statement should be used to timely dispose of objects which implement IDisposable. This does not actually clean managed memory but allows a managed object to release any unmanaged resources it may be holding and in some occasions remove references to managed objects to prevent memory leaks.
I suggest reading up on the following sites which provide in depth explanations of both IDisposable and the using statement
IDisposable, Finalizers and the definition of an unmanaged resource
http://www.codeproject.com/KB/dotnet/IDisposable.aspx

Whenever an object is disposable (it implements IDisposable interface) it means that it probably uses some unmanaged resources that can not be managed by garbage collector and therefore if your object is collected these resources might remain in the memory causing some problems. The solution for this problem is :
1.To implement IDisposable interface in such kind of objects and to clear/close unmanaged resources in Dispose method (for example if you are using a disposable object inside your object it'd be better to have a Dispose method to call its dispose inside)
2.To call the Dispose method of disposable objects when they are not needed anymore but be careful cause reusing a disposed object can throw some exceptions.
The using syntax that you mentioned is a short way of doing the same and it interprets this:
using(var obj=new myDisposableObject)
{
obj.Something();
}
into following :
var obj=new myDisposableObject();
try
{
obj.Something();
}
catch
{
throw;
}
finally
{
obj.Dispose();
}
thus you can always be sure that whatever happens the Dispose method of your object is always called.

You don't clean the memory; the object implementing IDisposable will clean its unmanaged resources in its Dispose method (or at least, that's the implication that the class is making by implementing IDisposable), and .NET will clean the memory when the object is collected.

still trying to understand the dispose pattern

i've read msdn and various posts about dispose pattern, and there are still a couple of things i don't understand. I've written the following code to test the dispose pattern. Please note that there aren't unmanged resources, i'm using vs2008 and .net 3.5 :
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void tryDispose()
{
//test 1 : allocate resource and leave manage it to gc
BL.myclass df = new BL.myclass();
//test 2 : try to force garbage collecting
//GC.Collect();
//test 3 : call dispose myself
//using (BL.myclass df = new BL.myclass())
//{
//}
}
private void button1_Click(object sender, EventArgs e)
{
tryDispose();
}
this is my disposable class:
class myclass: IDisposable
{
private StronglyTypedDs myDS;
private bool _disposed;
public myclass()
{
using (myDSTableAdapter docDocadpt = new myDSTableAdapter())
{
myDS = new StronglyTypedDs();
docDocadpt.Fill(myDS.TheTable);
}
}
#region IDisposable Members
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
~myclass()
{
Dispose(false);
}
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
if (myDS != null)
myDS .Dispose();
myDS = null;
}
}
_disposed = true;
}
#endregion
}
The results are :
test 1a - just instantiating myclass, the destructor is commentend since myclass doesn't contains unmanaged resources : myclass.dispose is not called, even if i close the application (whose dispose is executed instead) . So what's the state of the dataset once i close the application ?
test 1b - uncommenting destructor, it's ok all disposes are called when i close the application.
test 2a and 2b - i do the above test just calling gc.collect : the behaviour is identical to test 1a and 1b respectively
test 3 - everything works fine (of course)
many posts says that, if myclass doesn't contains unmanaged resources, i don't need to add the destructor; yet in my tests , if i don't add the destructor , myclass.dispose doesn't get called when i close the application. I haven't waited for the gc to run by itself (if i remember correctly gc.collect doesn't guarantes the class instance is deallocated) to check if it will call myclass.dispose .
So what's the correct implemention : always define e destructor or avoid it if myclass contains only managed resources ?
If i had filled all generations levels, would had the gc called myclass dispose or not without having implemented a destructor?
Finally i've noticed that if i define a destructor , but don't declare the class as implementing IDisposable, the disposing chain works anyway. This could make sense since the destructor might be translated to finalize in IL. But i find it really confusing : is it some kind of "implicit" interface implementation i don't know? gc can dispose the item but users can't
thank you in advance
Stefano

Trust your Garbage Collector. Managed resources will get cleaned up, eventually. There is no need for a finalizer or implementing IDisposable unless you have some external resource that needs to be released.
This typically means that you only should implement IDisposable when you either:
Are wrapping a native resource. (In this case, you probably also want a finalizer.)
Are encapsulating a class which implements IDisposable. (In this case, you want IDisposable, but don't need to implement a finalizer/destructor.)
Part of the confusion with IDisposable, in my opinion, is that it covers quite a few use cases, and the proper implementation changes depending on what you're doing (ie: wrapping native resources, wrapping other IDisposable classes, or using Factored types). To address this, I've written a multiple part series on IDisposable - it might help clarify some of this for you.

The correct pattern is to only use a finalizer when your class contains unmanaged resources. As to relying on the GC to dispose of your managed objects, don't. The IDisposable contract makes it clear that this object needs to be disposed.

Ok i think i've understood, referring to my example its correct to implement a dispose because the dataset is global to my class and implements IDisposable , while i don't need the finalizer because there aren't unmanaged resources.
Even if i "forget" to dispose some managed resource in my class dispose method, the gc will collect it at some point. The dispose method is just an utility i provide to other classes/developers for managed resources, a must with the finalizer if i wrap unmanaged resources .
i'll read the articles you have provided asap, but in the mean time i've the last question : when gc will free memory owned by my class and its resources ? when someone calls dispose or when it will run (it will free memory instead of moving it to next generation ) ?
thank you everybody for your answers and examples

I wrote a brief seris entitled How to Implement IDisposable and Finalizers: 3 Easy Rules. It describes a much simpler approach that Microsoft themselves have followed since the 2.0 version of the BCL.
The "official" pattern is needlessly complex and needlessly confusing.

Your code is correct, you've implemented it exactly like it is documented in the MSDN library.
You'll need to take a second look though. Reason what happens when the destructor (aka finalizer) runs. The disposing argument will be false, the protected Dispose method does nothing. This is entirely normal, finalizers should only ever release unmanaged resources. You don't have any. It is extraordinary rare to ever have an unmanaged resource in your own code. They belong in the nice wrapper classes available in .NET to turn an unmanaged operating resource into a nice managed class. If you find yourself thinking you need a finalizer, you'll be wrong 99.99% of the time. Even if you do wrap an unmanaged resource, you should use one of the SafeHandle wrappers. And rely on their finalizers.
Okay, you want to get rid of the destructor. It isn't healthy to leave it in, it keeps the object in memory longer than necessary. When you do, you'll cut it down to:
public void Dispose()
{
if (myDS != null) myDS.Dispose();
}
Which is the boiler-plate implementation of most any Dispose() method, just call the Dispose method of members of the class. You can completely omit it if you don't have any members with a Dispose() method.
Next, you do misunderstand how the Dispose() method gets called. It is not automatic. Which is the point of having it in the first place, releasing resources automatically is already taken care of by the garbage collector. The Dispose() method is there for you to call, either with the using statement or calling it directly. So that you can release the resource early instead of waiting for the garbage collector finalizer thread to get around to it. Which can take a while. Call it when you know that your program won't be using the object anymore.
If your DataSet is actively used by the form then you cannot dispose it until the form closes. Call the class' Dispose() method in a FormClosed event handler. Or, better, open the form's Designer.cs file, cut-and-paste the Dispose() method you find in there and move it to the form's source code file. And add the dispose call. I know that's a bit confuzzling, but the only time it's okay to edit the designer file.

The main purpose of IDisposable is to have a consistent standard interface you can dispose of unmanaged resources with, that is if you didn't do something to ensure Dispose() was called these resources would hang around after the app was closed. Also understood by the using() syntax, that is using will implement the following block for you:
DisposableType someDisposable = new DisposableType();
try
{
// Do whatever
}
finally
{
((IDisposable)someDisposable).Dispose();
}
This is all implemented in a nice design like so:
using(DisposableType someDisposable = new DisposableType())
{
// Do whatever
}

Consider a "disposable" keyword in C#

What are your opinions on how disposable objects are implemented in .Net? And how do you solve the repetitiveness of implementing IDisposable classes?
I feel that IDisposable types are not the first-class citizens that they should've been. Too much is left to the mercy of the developer.
Specifically, I wonder if there should'nt have been better support in the languages and tools to make sure that disposable things are both implemented correctly and properly disposed of.
In C# for instance, what if my class that needs to implement the disposable semantics could be declared like this:
public class disposable MyDisposableThing
{
~MyDisposableThing()
{
// Dispose managed resources
}
}
The compiler could in this case easily generate an implementation of the IDisposable interface. The destructor ~MyDisposableThing could be transformed into the actual Dispose method that should release managed resources.
The intermediate C# code would look like this:
public class MyDisposableThing : IDisposable
{
private void MyDisposableThingDestructor()
{
// Dispose my managed resources
}
~MyDisposableThing()
{
DisposeMe(false);
}
public void Dispose()
{
DisposeMe(true);
GC.SuppressFinalize(this);
}
private bool _disposed;
private void DisposeMe(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
// Call the userdefined "destructor"
MyDisposableThingDestructor();
}
}
_disposed = true;
}
}
This would make for much cleaner code, less boilerplate disposing code, and a consistent way of disposing managed resources. Implementing IDisposable by hand would still be supported for edge cases and unmanaged resources.
Ensuring that instances are properly disposed is another challenge. Consider the following code:
private string ReadFile(string filename)
{
var reader = new StreamReader();
return reader.ReadToEnd(filename);
}
The reader variable never outlives the scope of the method but would have to wait for the GC to dispose it. In this case, the compiler could raise an error that the StreamReader object was not explicitly disposed. This error would prompt the developer to wrap it in a using statement:
private string ReadFile(string filename)
{
using (var reader = new StreamReader())
{
return reader.ReadToEnd(filename);
}
}

An oft-stated principle is that "design patterns are needed to address language deficiencies". This is an example of that principle. We need the disposable pattern because the language doesn't give it to you.
I agree that disposability could have been elevated out of the "pattern" world and into the C# language proper, as we did with, say, property getters and setters (which are standardizations of the pattern of having getter and setter methods), or events (which standardize the idea of storing a delegate and calling it when something interesting happens.)
But language design is expensive and there is a finite amount of effort that can be applied to it. Thus we try to find the most useful, compelling patterns to put into the language proper. And we try to find a way that does so in a way that is not merely convenient, but actually adds more expressive power to the language. LINQ, for example, moves the concepts of filtering, projecting, joining, grouping and ordering data into the language proper, which adds a lot of expressive power to the language.
Though this is certainly a good idea, I don't think it meets the bar. It would be a nice convenience, I agree, but it doesn't enable any really rich new scenarios.

In addition to the other answers, there is the problem of how much should this implement and what should people expect from it? Say I declared my class like this:
public disposable class MyClass
{
readonly AnotherDisposableObject resource = new AnotherDisposableObject();
~MyClass()
{
this.resource.Dispose();
}
public void DoStuff()
{
this.resource.SomeMethod();
}
}
Then what would you expect to happen if a caller called DoStuff after the instance had been disposed? Should the compiler automatically insert something like
if (this.disposed) throw new ObjectDisposedException();
at the start of every method because you have declared the class as disposable?
If so then what about cases where methods are explicitly allowed to be called after an object is disposed (e.g. MemoryStream.GetBuffer)? Would you have to introduce a new keyword that indicated this to the compiler, e.g. public useafterdispose void ...?
If not then how do you explain to people that the new keyword implements some of the boiler-plate code for you, but that they still need to write code to check whether the object is disposed in each method? Moreover, how can they even check this, because all the state information about whether the object has been disposed is auto-generated! Now they need to track their own flag in the ~MyClass method which undoes half the work the compiler should be doing for you.
I think as a specific language pattern there are too many holes in the concept, and it only attempts to solve one specific problem. Now what could solve this entire class of problem in a general-purpose fashion is mixins (i.e. a Disposable mixin) and this language feature would be generally reusable for different concepts (e.g. Equatable mixin, Comparable mixin, etc.). That's where my money would go.

Personally, I consider the support for IDisposable to be quite decent in the current version of .NET. The presence of the using keyword pretty much makes it into a first-class construct for me.
I do admit there is a certain amount of boilerplate code involved, but not enough to warrant a new language features. (Auto-implemented properties was a good example of a feature that was begging to be introduced.) You've missed out an important point in your post that this "boilerplate" code is not always what you need. Mainly, you need to dispose unmanaged resources outside of the if (disposing) block.
Of course, the destructor (~MyDisposableThing) and parameterless Dispose() method are genuinely boilerplate and could be eliminated by the user of a language keyword, as you suggest - but again I'm not sure the introduction of an actual new keyword is all that necessary for a few lines of code.
I certainly see the point you are making here, and do sympathise with it to some degree. (I'm sure no coder would complain if your suggestion becamse part of the language specification.) However, it's not likely to convince the .NET development team when there are a rather limited number of lines of code anyway, some of which are arguably fairly context-specific (and thus not boilerplate).

I completely agree that IDisposable needs better language suppprt. Here's my variant of it from a while ago. The details are probably wrong, but C++/CLI serves as a pretty good model for this. Unfortunately it confuses the hell out of C# programmers when I show them examples in C++/CLI. But it already does "the right thing" in terms of implementation; we would just need a new syntax in C#.
Even the simplest Windows Forms application has a Dispose method in it, which is generated by a wizard and is fragile in the face of inexpert changes. The idea of composing components together such that one component can "own" several others is so fundamental that IDisposable is practically unavoidable, and unfortunately it seems to take several pages of most books to explain how to implement it correctly.
The existing using statement takes care of the client side. Where we need more language support is on the implementation side.
Some of the fields of a class are references to things that the class "owns", and some not owned. So we have to be able to mark a field as owned.
Also, it would be a very bad idea to automatically generate a finalizer. Most often, a class will own other objects that implement IDisposable. Not all classes are thread safe, nor should they need to be. If they are called from a finalizer, that happens on another thread, forcing them to be thread safe. This is probably the one area around IDisposable that causes the most confusion - a lot of people read the books and come away with the mistaken impression that you have to write a finalizer on an object that supports IDisposable.

I realize this is an old thread but there is something that has been overlooked.
Dispose pattern in both C# and Java break the fundamental reason for not having a deterministic destructor.
MyObject A = new MyObject()
MyObject B = A;
A.Dispose();
What is the state of B now? What if the owner of B didn't really want it disposed. You now have the same issue in C++ where you have to keep track of all the references of objects you are holding on to.
IDisposable is only truly valid within the context of using() and ensuring resource cleanup if an exception occurs.
There are design patterns to do this but it isn't IDisposable
#Peter Yes I am arguing that the Dipsosable pattern has a fault. When implemented the Disposable pattern isn't normally meant to just dispose OS resources with the idea of being able to continue using the object that was disposed. By using the Disposable pattern outside of a try{} finally{} in Java or using() in .NET you break one of the reasons of having a GC. I am not saying memory will leak. I am saying you can now have other parts of the code that have a reference to an Object that has been disposed. Now the onus is back on the developer to check if an object has been disposed before each call, or at the very least catch a ObjectDisposedException.
Lets look at a silly example:
FileStream stream = new FileStream (#"c:\mylog.txt");
logger.setStream (stream);
Who is supposed to invoke .Dispose()? It may not be obvious that the logger is now aquiring ownership of the file stream. Let's say the stream was created somewhere else outside of the developer knowing it will be set as the logging stream.
if we were to add one line, we would break the logger
using (FileStream stream = new FileStream (#"c:\mylog.txt"))
{ logger.setStream (stream); }
or
FileStream stream = new FileStream (#"c:\mylog.txt");
logger.setStream (stream);
stream.Dispose();
The Disposable pattern does not reference count for resources. The developer now has to be conscious of who owns the object and who is responsible for cleaning it up. The real problem is that when Dispose() is invoked the normal behavior is to invalidate the whole object preventing it from being used.

IMHO, the .net languages have a major shortcoming in their handling of iDisposable, which is that there is no nice way of handling initializers that throw exceptions. Unless one 'leaks' a copy of the object under construction or the disposable objects therein, there's no way to clean up any iDisposable objects which were created (either in an initializer, or a base-level constructor) before an initializer throws.
Two features I would like to see toward that end:
A class declaration that would cause a particular method to be invoked if an exception throws out of its constructor.
A field declaration which would indicate that the field should have .Dispose called upon it if some special private method or keyword is used on the object.
BTW, I would also like to see a declaration available for structure methods which would indicate that the method alters the underlying structure. Use of such methods would be forbidden on structure rvalues, and use of such methods on structure properties would generate a read-modify-write sequence.

Okay you need to understand the difference between managed and unmanaged memory.
Put simply, c++ style destructors wouldn't work in the managed world of c# because there's no guarantee when the object gets garbage collected, hence you would never know when the destructor would get called, which would make things very unpredictable.
As opposed to c++, when destructors get called as soon as the class goes out of scope, so you can guarantee when it gets called.
This is the reason why c# can't have destructors.