I want to created a method that calls a repository class in a using() statement. That class is not currently disposable. Is there anything I should consider before making it implement IDisposable?
i.e.
using(var repo = new RespositoryClass() )
{
//do work
}
You should implement IDisposable if the class uses unmanaged resources, or initializes other members that implement it. Otherwise, don't use it if you don't need it.
Just because you use an IDisposable object inside a class does not mean that the class needs to implement IDisposable.
The example class below doesn't need to implement IDisposable.
class NotDisposable
{
public void someMethod()
{
using(SomethingDisposable resource = new SomethingDisposable ())
{...}
}
}
Here is an example of a class that would need to implement IDisposable.
class SomethingToDispose : IDisposable
{
private SomethingDisposable resource = new SomethingDisposable();
public void someMethod()
{
//code that uses resource
}
//code to dispose of "resource" in a Dispose method.
}
As you can see in this second example there isn't really anywhere for the class to put a using statement to dispose of the resource. Since it's storing the disposable object in a field, and it is the one responsible for disposing of it, the best way of ensuring that it gets disposed is to implement IDisposable.
Related
I am just inheriting IDisposable interface in my class like this.
public class Program3:IDisposable
{
}
When I am creating an instance to the above class, I want to dispose the object manually or the object disposed by it automatically?
Note : I am not using Dispose method explicitly to dispose the object
You have to implement IDisposable interface methods:
public void Dispose()
{
// Clear all unmanaged resources
}
Whenever you then instantiate your object you should do it inside a using statement
using(Program3 p3 = new Program3())
{
//do your job
} // here the p3.Dispose gets called
It is important to note that the point of Dispose is to free unmanaged resources. What you get in. Net is already managed, so only if you are implementing something of your own should you use IDisposable.
I have a class which has a property of the type SqlConnection. SqlConnection implements IDisposable. I have following questions:
Should my class also implement IDisposable just because it has property of type IDisposable?
If yes, do I need to Dispose the property explicitly when I am disposing instance of my class? E.g.
public class Helper : IDisposable
{
// Assume that it's ANY OTHER IDisposable type. SqlConnection is just an example.
public SqlConnection SqlConnection { get; set; }
public void Dispose()
{
if (SqlConnection!= null)
{
SqlConnection.Dispose();
}
}
}
Note :
I know that there is a pattern to be followed while implementing IDisposable but my question is very specific to the case mentioned above.
Yes
Yes
There even exists a Code Analysis rule for that: CA1001: Types that own disposable fields should be disposable.
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.
EDIT: the above answer is always valid for IDisposable members that are owned by the parent class.
That said, the ownership of a member is kinda vague for public properties like yours: if the SqlConnection instance is created outside your class, chances are your class is not actually owning the instance, but nobody knows that except you.
There is a funny example about whether an IDisposable member is owned or not by its parent class: StreamWriter. There are lots of question about it, see for example this thread: Is there any way to close a StreamWriter without closing its BaseStream?
Now there even is a leaveOpen parameter so the StreamWriter doesn't dispose its base stream.
It depends. If your class creates and owns the IDisposable it must dispose it (so, both answers are "yes").
If your class just uses IDisposable it must not dispose it (so the first answer is, usually, "no" and the second answer is "no").
In your case, it seems that Helper class
public class Helper
{
// Note, that you can assign any arbitrary Connection via this property
public SqlConnection SqlConnection { get; set; }
....
}
just uses SqlConnection (because it provides "set") in the way like
// It's not helper that owns SqlConnection
using (SqlConnection con = new SqlConnection(...)) {
...
// helper just uses Connection, so helper must not dispose it
Helper helper = new Helper() {
SqlConnection = con;
};
...
}
so it must not dispose the connection. On the contrary, a class like that
public class Helper: IDisposable {
private SqlConnection m_SqlConnection;
// Note the absence of public "set"
public SqlConnection SqlConnection {
get {
return m_SqlConnection;
}
}
...
}
owns its SqlConnection so it's responsible for disposing it:
using (Helper helper = new Helper(...)) {
...
// it's helper that owns SqlConnection
SqlConnection con = helper.SqlConnection;
...
}
Yes for both - if your class is responsible for the lifecycle of a member field, then it needs to call Dispose on that object, which means your class needs to implements IDisposable so that the member can be disposed at the correct time.
However, note that you likely don't want to use a public settable property for such a member, as then anyone can clear, dispose, unset, reset that field directly. Your class needs to maintain control of that field, which means it should only be settable from inside the class itself - ideally using a private readonly field or readonly property.
Trying to understand when implementation of IDisposable is necessary:
I wrote a little example.
public class FileManager
{
private FileStream fileStream;
public void OpenFile(string path)
{
this.fileStream = File.Open(path, FileMode.Open, FileAccess.Read);
}
public void CloseFile(string path)
{
if ( this.fileStream != null && this.fileStream.CanRead)
{
this.fileStream.Close();
}
this.fileStream.Dispose();
}
}
// client
var manager = new FileManager();
manager.Open("path");
manager.Close("path");
Does this class need to implement IDisposable because it has a managed resource (FileStream) which holds onto an unmanaged resource (a file)? Or do I not have to implement IDisposable because I am cleaning up within the class?
Confused.
For every instance of any type which implements IDisposable and might do so in a non-trivial fashion, it must at every moment be possible to identify how that instance will be Disposed. In most cases, this means that each IDisposable instance will have a well-defined owner, which is responsible for calling Dispose. In the case of the FileStream instance created by the class, your class is the owner, since nothing else will be able to Dispose it.
Classes with fields that references to IDisposable instances which they own should almost always implement IDisposable, and use their Dispose method to Dispose the IDisposable objects they own. Your class has such a field; it should thus implement IDisposable.
Whenever possible, a class which requires cleanup should be designed so that calling IDisposable.Dispose on it will suffice to perform any and all such cleanup as may be needed. In some cases, it may be impractical to perform cleanup without using some other method, but those cases are pretty rare. If one can design a class so that Dispose will take care of all necessary cleanup, one should do so.
You will probably want to implement IDisposable, in the event that you (or another developer) use your FileManager class and forget to close it. Note how the example for IDisposable puts a call to Dispose(false) in the finalizer.
Why are you passing the path to the close method? In your case, it seems your manager can open different files if they are close before opening another one, so you won't want to dispose that object.
IMHO, I would prefer to implement it this way:
public class FileManager : IDisposable
{
private string path;
private FileStream fileStream;
public FileManager(string path)
{
this.path = path;
}
public void OpenFile()
{
this.fileStream = File.Open(path, FileMode.Open, FileAccess.Read);
}
public void CloseFile()
{
if ( this.fileStream != null && this.fileStream.CanRead)
{
this.fileStream.Close();
this.fileStream.Dispose();
}
}
public void Dispose(){
this.CloseFile();
}
}
// client
var manager = new FileManager("path")){
manager.OpenFile();
//Do other stuff
manager.CloseFile()
or
using( var manager = new FileManager("path")){
manager.OpenFile();
//Do other stuff
}
In the case that you call your Close method, you don't need to separately dispose. However, general practise in this case would be to implement IDisposable because there's no guarantee that a consumer of the class would call Close.
You can only reliably leave out IDisposable if a resource is created and then disposed within the same method, because that's the only way you can be sure that the resource is definitely disposed of after use.
You should implement IDisposable.
Imagine:
var manager = new FileManager();
manager.Open("path"); // <- throws for some reason
manager.Close(); // <- then this never gets called
Of course you could now put a try/finally around it like that:
try {
var manager = new FileManager();
manager.Open("path");
}
finally {
manager.Close();
}
... but that's exactly what using and IDisposable have been invented for, with which you can comfy write:
using (var manager = new Manager()) {
manager.OpenFile("path");
} // and CloseFile will automagically be called here.
Don't see any real benefits in implementing IDisposable here, if not declarative ones. If someone sees your class implements IDisposable he understands that there are somewhere resources that have to be cleaned up after use. It's just a built-in .net convension of declaring types like this.
If you don't use that pattern, you are free to do that , but you violate suggested and mainly followed by community guidelunes for .net type declaration.
Basically I have a few functions that look like this:
class MyClass
{
void foo()
{
using (SomeHelper helper = CreateHelper())
{
// Do some stuff with the helper
}
}
void bar()
{
using (SomeHelper helper = CreateHelper())
{
// Do some stuff with the helper
}
}
}
Under the assumption I can use the same resource instead of a different one [instance] in every function is it ok practice in regard to cleanup and such to do this?:
class MyClass
{
SomeHelper helper = CreateHelper();
// ...foo and bar that now just use the class helper....
~MyClass()
{
helper.Dispose();
}
}
No, do not add a destructor (Finalizer).
You can reuse the resource but then your class has to implement IDisposable.
sealed class MyClass : IDisposable
{
SomeHelper helper = CreateHelper();
// ...foo and bar that now just use the class helper....
//~MyClass()
public void Dispose()
{
helper.Dispose();
}
}
And now you have to use MyClass instances in a using block. It self has become a managed resource .
A destructor is of no use, whenever a MyClass instance is being collected the associated helper object will also be in the same collection. But having a destructor still incurs considerable overhead.
The standard pattern for IDisposable uses a virtual void Dispose(bool disposing) method but when making the class sealed you can use the minimalistic implementation above.
In .NET you don't know when (or whether) finalizer is called at all.
Instead, explicitly indicate that your class is to be disposed of by implementing IDisposable:
(This is exactly what SomeHelper does)
class MyClass : IDisposable
{
readonly SomeHelper helper = CreateHelper();
// any method can use helper
public void Dispose()
{
helper.Dispose();
}
}
using(var myObj = new MyClass()) {
// at the end, myObj.Dispose() will trigger helper.Dispose()
}
I used readonly to ensure helper doesn't get re-assigned somewhere else in the class, but this really doesn't matter if you're careful.
You must be extra careful to never set it to null, or your Dispose will throw an exception. If the field is protected, you can check for nullity before calling Dispose on it so you know you're playing safe.
You can share such a resource during the lifetime of your object, in which case it is recommended that you implement IDisposable.
No, it is not. You don't know when the finalized will un. Also, if your resource is managed, it will be disposed of at some point without the finalized.
If you don't want to use using all the time, perhaps ou can use it once around many functions.
You don't need to override the finalizer in your object, which you have shown in your second code sample by ~MyClass().
You will need to implement the IDisposable pattern. You haven't been explicit in your question if you are using managed and unmanaged resources, but here's a quick sample for a managed resource. Stackoverflow has a myriad of examples on this. Reed Copsey also has a good series on it, and you can start here.
class MyClass : IDisposable
{
private bool _Disposed;
private SomeHelper _Helper;
protected virtual void Dispose()
{
this.Dispose(true);
}
public void Dispose(bool disposing)
{
if (_!Disposed && disposing)
{
if (_Helper != null)
_Helper.Dispose();
_Disposed = true;
}
}
}
The convention is that if your class owns an IDisposable object it should also implement IDisposable. So rather than implementing a finalizer your class should implement IDisposable and dipose of the helper there.
One problem with implementing the finalizer is that you have no control over when it's being called. The disposable pattern gives you a more deterministic way of cleaning up resources.
My question is why do I need IDisposable? I have a class that consumes some resources
that need to be freed. I have two options
Without IDisposable
class SomeUtilityClass
{
public Stop()
{
// free resources
}
}
With IDisposable
class SomeUtilityClass, IDisposable
{
public void Dispose()
{
// free resources
}
}
So why do I need IDisposable here? It does not matther how to name the function.
class Program
{
public Main(..)
{
SomeUtilityClass _class = new SomeUtilityClass();
// clean up when we've done
_class.Stop();
// OR
_class.Dispose();
}
}
Because IDisposable is supported by C# and you can use cool using syntax:
using (IDisposable someDisposable = new ...)
{
// your code with someDisposable
}
This is actually transformed by compiler to something like:
IDisposable someDisposable = new ...
IDisposable someDisposable2 = someDisposable ;
try
{
// your code with someDisposable
}
finally
{
if (someDisposable2 != null)
{
someDisposable2.Dispose();
}
}
So if any exception happens inside using block your object would be disposed anyway.
You should only really use IDisposable when your class consumes unmanaged resources, and they need to be freed immediately (streams, db etc).
It also provides a way for the CLR to 'clean up' when there are unhandled exceptions that cause your thread to be unloaded.
Calling IDisposable marks the object as being available for garbage collection immediately, but if not implemented correctly you can cause your object to be promoted a garbage collection generation which can cause memory pressure (refer to Jeffery Richters CLR via c# 3 if you want a full explanation).
a quick google turned this up:
http://kleahy-technical.blogspot.com/2009/01/idisposable-and-garbage-collection.html
i suggest you read into the IDisposable pattern, when to use it, when not to and its implications on GC and state.
EDIT:
there is loads of info on stackoverflow too:
Use of Garbage Collection?
Well in your case, there is not much point implementing IDisposable, since you can manually dispose of your resources.
A common use of IDisposable is when you expose an interface that handles data connections, and you want all derived classes to dispose when they're done.
Consider this:
public interface IDataCtx
{
void CallDB();
}
public class MyDataCtx : IDataCtx
{
private SqlConnection dc;
public MyDataCtx() { dc = new SqlConnection(); dc.Open(); }
public void CallDB();
{
dc.Something();
}
}
Allowing you to do something like this:
IDataCtx ctx = new MyDataCtx();
ctx.CallDB();
But wait, what about that open connection? Uh oh!
If you made IDataCtx : IDisposable (and implemented the code in your derived ctx), you could do this:
IDataCtx ctx;
using (ctx = new MyDataCtx())
{
ctx.CallDB();
}
Guaranteeing that whatever implementation of IDataCtx you use, it will always be disposed of (even in the case of an exception).
That's how i use it anyway. (plus it's just good practice).
IDisposable interacts with the using keyword to make it easy to clean up after yourself, e.g.:
using (var file = new FileStream(...))
{
file.Write(...);
}
In the above code, the FileStream is closed as soon as the using block completes, rather than waiting around to be garbage-collected.
It's a convention used in the C# language.
You also get the nifty using statement to your disposal.
using (SomeUtilityClass _class = new SomeUtilityClass()) {
} // Dispose is automatically called
As well as being able to use the using statement, it also give the garbage collector a hint that the object can be removed from memory.
If your class owns unmanaged resources or your class owns managed IDisposable resources you should in generel implement the IDisposable interface.
An easy readable little article on when to implement IDisposable and Finalizers can be found here: http://nitoprograms.blogspot.com/2009/08/how-to-implement-idisposable-and.html