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Is Close() same as Using statement

Is Close() same as Dispose() or using statement. Is it necessary to call using statement even if Close is called?.
I know before disposing of an object, close should be called, so we close the resource and may it available to Dispose.
https://msdn.microsoft.com/en-us/library/aa355056(v=vs.110).aspx
says Close is same as Dispose.

Is Close() same as Using statement?
No it is not.
Should you call Close() after a using?
No, it will break due to access to the disposed object.
Should I call Close() before exiting the using block?
It's complicated. If the IDisposable interface is implemented correctly: no. Otherwise: possibly.
Close() has no relation to IDisposable interface, see: https://msdn.microsoft.com/en-us/library/system.idisposable(v=vs.110).aspx
using only applies to IDisposable inherited objects, see: https://msdn.microsoft.com/en-us/library/yh598w02.aspx
Thus:
Close() and Dispose() may not considered to be related in any way.
When the IDisposable interface is correctly implemented, you may assume all clean-up necessary will be carried out. This implies an internal call to a Close() method would be carried out. This means that an explicit call to Close() should not be necessary.
The other way round; when a object is of type IDisposable and exposes a Close() method, a call to Close() will not be sufficient to properly dispose/clean-up the object. Dispose() must still be called, you can do this directly, or through the using statement.
You can also let the garbage-collector handle the Dispose() call for you (if its correctly implemented, see: Proper use of the IDisposable interface) But this is considered bad-practice, since you need to rely on a proper implementation and have no direct control over the GC timing.
Please note, a reason to implement a Close() function, is usually to give a developer a way to reuse the object. After calling Dispose() the object is considered to be marked for finalization and may not be used any more.

The using pattern is useful because it includes a try ... finally ... that will protect against exceptions...
If you do:
FileStream fs = null;
try
{
fs = File.OpenRead("MyFile.txt");
}
finally
{
if (fs != null)
{
fs.Close();
}
}
then in this case it would be nearly equivalent (because the Stream.Close() calls the Dispose(true))
BUT it is still "wrong"... You use using for IDisposable classes unless you have a very very good reason (there are some reasons for not doing it... Sometimes the lifetime of an object is very very difficult to track. In that case it is normally ok to no Dispose() it.).
The concept of a pattern is that it should become part of you... If you try to skirt from a pattern, then before or later you'll forget about it... And for what? For writing MORE lines that are MORE error-prone?

Not necessarily. I can write a class that has a Close and a Dispose method that aren't related.
class Foo : IDisposable
{
public void Close() { DoBar(); }
public void Dispose() { DoBaz(); }
}

Order of disposal for base classes

When a derived class overrides Dispose should the base class Dipose be called first before the derived class disposes of any local resources?
The reason I ask is because someone on our team is saying yes for every scenario, I'm trying to work out if this is good idea or just 'cargo cult' programming, I don't have a strong view either way.
Before:
public override void Dispose()
{
base.Dispose();
if (!_isDisposed)
{
_isDisposed = true;
if (_foo != null)
{
_foo.Dispose();
}
}
}
After:
public override void Dispose()
{
if (!_isDisposed)
{
_isDisposed = true;
if (_foo != null)
{
_foo.Dispose();
}
}
base.Dispose();
}
Note: I'm not looking for how to implement the basic dispose pattern but more clarification from peoples experiences.

"It depends"
You can't have a hard-and-fast rule for this, because the order you need to call dispose will depend on the implementation of the classes.
Sometimes you might want it at the start, sometimes at the end, and sometimes in the middle. Most of the time, it probably won't matter.
Generally speaking, people seem to call it first (in the absence of any other reason to call it at a different time).
One reason to lean towards calling it first is that then the derived class has a chance to do special stuff afterwards if it needs to.

You should think about the consequences of the different approaches. In most cases, the IDisposable objects owned by the base class will be independent of those owned by the derived class, and the order of disposal won't matter, provided none of the Dispose methods throws an Exception (*).
If it's critical to release an IDisposable resource, you could consider using try/finally to ensure all Dispose methods are called - but this isn't universally done. For example, the System.Component.Container class manages and disposes multiple IDisposable objects, but makes no attempt to ensure they are all disposed if an exception is thrown.
(*) It's perfectly legitimate for Dispose to throw: for example a FileStream might attempt to flush data to a network resource that's no longer available during Dispose.

Dispose object in the reverse order to create. So firstly is created base class, so it should be dispose in the end, and so on...

IDisposable Question

Say I have the following:
public abstract class ControlLimitBase : IDisposable
{
}
public abstract class UpperAlarmLimit : ControlLimitBase
{
}
public class CdsUpperAlarmLimit : UpperAlarmLimit
{
}
Two Questions:
1.
I'm a little confused on when my IDisposable members would actually get called. Would they get called when an instance of CdsUpperAlarmLimit goes out of scope?
2.
How would I handle disposing of objects created in the CdsUpperAlarmLimit class? Should this also derive from IDisposable?

Dispose() is never called automatically - it depends on how the code is actually used.
1.) Dispose() is called when you specifically call Dispose():
myAlarm.Dispose();
2.) Dispose() is called at the end of a using block using an instance of your type.
using(var myAlarm = new CdsUpperAlarmLimit())
{
}
The using block is syntactic sugar for a try/finally block with a call to Dispose() on the object "being used" in the finally block.

No, IDisposable won't be called just automatically. You'd normally call Dispose with a using statement, like this:
using (ControlLimitBase limit = new UpperAlarmLimit())
{
// Code using the limit
}
This is effectively a try/finally block, so Dispose will be called however you leave the block.
CdsUpperAlarmLimit already implements IDisposable indirectly. If you follow the normal pattern for implementing IDisposable in non-sealed classes, you'll override void Dispose(bool disposing) and dispose your composed resources there.
Note that the garbage collector does not call Dispose itself - although it can call a finalizer. You should rarely use a finalizer unless you have a direct handle on unmanaged resources though.
To be honest, I usually find it's worth trying to change the design to avoid needing to keep hold of unmanaged resources in classes - implementing IDisposable properly in the general case is frankly a pain. It's not so bad if your class is sealed (no need for the extra method; just implement the Dispose() method) - but it still means your clients need to be aware of it, so that they can use an appropriate using statement.

IDisposable has one member, Dispose().
This is called when you choose to call it. Most typically that's done for you by the framework with the using block syntactic sugar.

I'm a little confused on when my IDisposable members would actually get called. Would they get called when an instance of CdsUpperAlarmLimit goes out of scope?
No. Its get called when you use using construct as:
using(var inst = new CdsUpperAlarmLimit())
{
//...
}//<-------- here inst.Dispose() gets called.
But it doesn't get called if you write this:
{
var inst = new CdsUpperAlarmLimit();
//...
}//<-------- here inst.Dispose() does NOT get called.
However, you can write this as well:
var inst = new CdsUpperAlarmLimit();
using( inst )
{
//...
}//<-------- here inst.Dispose() gets called.

The best practice recommend when you implement Dispose() method in non sealed class you should have a virtual method for your derived classes to override.
Read more on Dispose pattern here http://www.codeproject.com/KB/cs/idisposable.aspx

when using an IDisposable object, it's always good to use it this way:
using(var disposable = new DisposableObject())
{
// do you stuff with disposable
}
After the using block has been run, the Dispose method will be called on the IDisposable object. Otherwise you would need to call Dispose manually.

When someone calls .Dispose on it.
No, it already implements it through inheritance.

IDisposable is implemented when you want to indicate that your resource has dependencies that must be explicitly unloaded and cleaned up. As such, IDisposable is never called automatically (like with Garbage Collection).
Generally, to handle IDisposables, you should wrap their usage in a using block
using(var x = new CdsUpperAlarmLimit()) { ... }
this compiles to:
CdsUpperAlarmLimit x = null;
try
{
x = new CdsUpperAlarmLimit();
...
}
finally
{
x.Dispose();
}
So, back to topic, if your type, CdsUpperAlarmLimit, is implementing IDisposable, it's saying to the world: "I have stuff that must be disposed". Common reasons for this would be:
CdsUpperAlarmLimit keeps some OTHER IDisposable resources (like FileStreams, ObjectContexts, Timers, etc.) and when CdsUpperAlarmLimit is done being used, it needs to make sure the FileStreams, ObjectContexts, Timers, etc. also get Dispose called.
CdsUpperAlarmLimit is using unmanaged resources or memory and must clean up when it's done or there will be a memory leak

C# disposable objects

Are there some advices about how I should deal with the IDisposable object sequences?
For example, I have a method that builds a IEnumerable<System.Drawing.Image> sequence and
at some point I would need to dispose that objects manually, because otherwise this might lead to some leaks.
Now, is there a way to bind the Dispose() call to garbage collector actions, because I want these objects disposed right in the moment they are no longer accessible from other code parts?
**Or maybe you could advice me some other approach? **
Generally, this seems to be the same problem as it comes, for example, in unmanaged C++ without shared pointers, where you can have a method:
SomeObject* AllocateAndConstruct();
and then you can't be sure when to dispose it, if you don't use code contracts or don't state something in the comments.
I guess the situation with disposable objects is pretty the same, but I hope there is an appropriate solution for this.

(from the question)
Now, is there a way to bind the
Dispose() call to garbage collector
actions, because I want these objects
disposed right in the moment they are
no longer accessible from other code
parts?
GC doesn't happen immediately when your object goes out of scope / reach; it is non-deterministic. By the time GC sees it, there is no point doing anything else (that isn't already handled by the finalizer), as it is too late.
The trick, then, is to know when you are done with it, and call Dispose() yourself. In many cases using achieves this. For example you could write a class that implements IDisposable and encapsulates a set of Images - and wrap your use of that encapsulating object with using. The Dispose() on the wrapper could Dispose() all the images held.
i.e.
using(var imageWrapper = GetImages()) {
foreach(var image in imageWrapper) {
...
}
// etc
} // assume imageWrapper is something you write, which disposes the child items
however, this is a bit trickier if you are displaying the data on the UI. There is no shortcut there; you will have to track when you are done with each image, or accept non-deterministic finalization.

If you want to determiniscally dispose of the objects in the collection, you should call Dispose on each:
myImages.ToList().ForEach(image => image.Dispose());
If you don't do this, and if your objects become unreachable, the GC will eventually run and release them.
Now, if you don't want to manually code the Dispose calls, you can create a wrapper class that implements IDisposable and use it through a using statement:
using (myImages.AsDisposable()) {
// ... process the images
}
This is the needed "infrastructure":
public class DisposableCollectionWrapper<D> : IDisposable
where D : IDisposable {
private readonly IEnumerable<D> _disposables;
public DisposableCollectionWrapper(IEnumerable<D> disposables) {
_disposables = disposables;
}
public void Dispose() {
if (_disposables == null) return;
foreach (var disposable in _disposables) {
disposable.Dispose();
}
}
}
public static class CollectionExtensions {
public static IDisposable AsDisposable<D>(this IEnumerable<D> self)
where D : IDisposable {
return new DisposableCollectionWrapper<D>(self);
}
}
Also notice that this is not the same as the situation you described with C++. In C++, if you don't delete your object, you have a genuine memory leak. In C#, if you don't dispose of your object, the garbage collector will eventually run and clean it up.

You should design your system in a way that you know when the resources are no longer needed. In the worst case, they'll be eventually disposed when the garbage collector gets to it, but the point of IDisposable is that you can release important resources earlier.
This "earlier" is up to you to define, for example, you can release them when the window that's using them closes, or when your unit of work finishes doing whatever operations on them. But at some point, some object should "own" these resources, and therefore should know when they're no longer needed.

You can use the 'using' block, to make sure, the IDisposable is disposed as soon the block is left. The compiler does encapsulate such blocks into try - finally statements in order to make sure, Dispose is called in any case when leaving the block.
By using a finalizer, one can make the GC call the Dispose method for those objects which where "missed" somehow. However, implementing a finalizer is more expensive and decreases the garbage collection efficiency - and possibly the overall performance of your application. So if any possible, you should try to make sure to dispose your IDisposables on your own; deterministically:
public class Context : IDisposable {
List<IDisposable> m_disposable = new List<IDisposable>();
public void AddDisposable(IDisposable disposable) {
m_disposable.Add(disposable);
}
public void Dispose() {
foreach (IDisposable disp in m_disposable)
disp.Dispose();
}
// the Context class is used that way:
static void Main(string[] args) {
using (Context context = new Context()) {
// create your images here, add each to the context
context.AddDisposable(image);
// add more objects here
} // <- leaving the scope will dispose the context
}
}
By using some clever design, the process of adding objects to the context may can get even more easier. One might give the context to the creation method or publish it via a static singleton. That way, it would be available for child method scopes as well - without having to pass a reference to the contex around. By utilizing that scheme it is even possible, to simulate an artificial destructor functionality like f.e. known from C++.

The neat method would be to create your own generic collection class that implements IDisposable. When this collection class is Disposed() ask for each element if it implements IDisposed, and if so Dispose it.
Example (look elsewhere if you don't know about the IDisposable pattern)
public class MyDisposableList<T> : List<T> : IDisposable
{
private bool disposed = false;
~MyDisposableList()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
}
protected void Dispose(bool disposing)
{
if (!disposed)
{
foreach (T myT in this)
{
IDisposable myDisposableT = myT as IDisposable;
if (myDisposableT != null)
{
myDisposableT.Dispose();
}
myT = null;
}
this.Clear();
this.TrimExcess();
disposed = true;
}
}
...
}
usage:
using (MyDisposableList<System.Drawing.Bitmap> myList = new ...)
{
// add bitmaps to the list (bitmaps are IDisposable)
// use the elements in the list
}
The end of the using statement automatically Disposes myList, and thus all bitMaps in myList
By the way: if you loaded the bitmap from a file and you forgot to Dispose() the bitmap you don't know when you can delete that file.

You can call GC.Collect() if you really was to dispose those objects right away but to my understanding it is up to the GC to decide whether to collect the memory.
This in turn will call the Finalize() method for each object that should be released.
Note that if the collection goes out of scope the GC will eventually collect the memory used by the images.
You can also use the using construct if you use a collection that implements IDisposeable. That will guarantee that the objects will be disposed exactly when the collection goes out of scope (or nearly after the end of the scope).

Why is calling Dispose() in a finalizer causing an ObjectDisposedException?

I have a NHibernate repository that looks like this:
public class NHibRepository : IDisposable
{
public ISession Session { get; set; }
public ITransaction Transaction { get; set; }
// constructor
public NHibRepository()
{
Session = Database.OpenSession();
}
public IQueryable<T> GetAll<T>()
{
Transaction = Session.BeginTransaction();
return Session.Query<T>();
}
public void Dispose()
{
if (Transaction != null && Transaction.IsActive)
{
Transaction.Rollback(); // ObjectDisposedException on this line
}
Session.Close();
Session.Dispose();
}
~NHibRepository()
{
Dispose();
}
}
When I use the repository like this, it runs fine:
using (var repo = new NHibRepository())
{
Console.WriteLine(repo.GetAll<Product>().Count());
}
But when I use it like this, it will throw an ObjectDisposedException:
var repo = new NHibRepository();
Console.WriteLine(repo.GetAll<Product>().Count());
The easy solution would be to always dipose of the repository explicitly, but unfortunately I don't control the life cycle of some of the classes that use the repository.
My question is, why is the Transaction disposed of already even though I did not explicitly call Dispose()? I'd like to have the repository automatically clean itself up if it was not disposed explicitly.

My question is, why is the Transaction disposed of already even though I did not explicitly call Dispose()?
Perhaps the transaction's finalizer ran first. Remember, finalizers of dead objects can run in any order and on any thread, and need not have been correctly initialized before they are finalized. If you do not understand all the rules of finalizers then learn them all before you attempt to write any more code that uses finalizers. This is one of the hardest things to get right.
It also looks as though you have implemented the disposable pattern incorrectly, and that is going to cause you a world of grief. Read up on the pattern and do it correctly; the finalizer should not be disposing stuff that has already been disposed:
http://msdn.microsoft.com/en-us/magazine/cc163392.aspx

Lose the finalizer. Very few classes in .net need a finalizer; generally, the only .net 2.0-or-later classes which should have finalizers are those whose sole reason for existence revolves around it.
If a class with a finalizer holds an access to some other object, one of three conditions will apply when the finalizer is run:
The other object has already had its finalizer (if any) run; there's no need to dispose it, since it's already been taken care of.
The other object has a finalizer scheduled to run; there's no need to dispose it, since it will be taken care of automatically.
A reference to the other object exists outside of the object whose finalizer is running; this usually means one shouldn't dispose it.
The only time a finalizer should ever take any action to dispose of a manage object is when an outside reference is likely to exist, and the collection of the object being finalized will imply that the other object should be disposed despite the existence of that reference. That's a very rare situation.

You should put GC.SuppressFinalize(this); in your Dispose method otherwise the finalizer will dispose an already disposed object. Also, finalizers are in almost all cases only needed for unmanaged resources

The CLR makes no guarantees with respect to the order that finalizers will be called. It sees a group of unrooted objects (e.g. not reachable from any GC root) and starts calling finalizers. It doesn't matter that you have connections within your object graph. The finalizers can be called in any order. Finalizers are intended to clean up unmanaged resources, not child objects. You need to re-think your API.

You should have a member variable isDisposed that would be set to true by the Dispose() method. Then at the beginning of the Dispose() command just return if it is already set to true. According to .NET whitepapers, Dispose() could be executed multiple times without side effects and this is the way to do it.
Secondly, make the class sealed (the class is not implementing the Dispose pattern properly for inheritance) and put GC.SuppressFinalize(this); right before the isDisposed variable assignment in the Dispose() method.
public void Dispose()
{
if (isDisposed) { return; }
....
GC.SuppressFinalize(this);
isDisposed = true;
}