Is it dangerous to use a memorystream as a private field in an instance class?
The class implements IDisposable:
class MyIDisposableClass:IDisposable{
private MemoryStream _stream;
//do stuff with _stream
void Dispose(){
_stream.Close();
_stream.Dispose();//does this statement make sense here ?
}
}
and will be used like this:
using(MyIDisposableClass() bla=new MyIDisposableClass())
{...}
Is that good approach or should I do something else, to give all class member access to that kind of information?
You're fine as long as you are wrapping your object in a using
After the using block the object's disposed method will get called. As long as you clean up everything you'll be fine.
And if you are worried about when it will be called the code here will show you.
using System;
public class DisposableExample : IDisposable
{
public void Dispose()
{
Console.WriteLine("Disposed");
}
}
public class Program
{
public static void Main()
{
Console.WriteLine("Before Disposing");
using(var disposableObj = new DisposableExample())
{
Console.WriteLine("Inside Using Statement");
}
Console.WriteLine("After Disposing");
}
}
This will print out
Before Disposing
Inside Using Statement
Disposed
After Disposing
See fiddle here
Related
Is there a .NET class which calls a method when it gets disposed, sometimes instead of:
try
{
...
}
finally
{
MyCleanupMethod()
}
I'd like to:
using(new OnDisposed(MyCleanupMethod))
{
...
}
Before I get berated, for three reasons:
For long try blocks it allows the reader to see what needs to be cleaned up at the start
try has an implication that its catching an error (which it's not)
To keep the disposal code private (if the IDisposable object is returned from a class)
Is this valid practice? If so, is a .NET class which does this?
You could add a constructor that takes the action:
public class OnDisposed : IDisposable
{
private readonly Action _disposeAction;
public OnDisposed(Action disposeAction)
{
_disposeAction = disposeAction;
}
public void Dispose()
{
// ...
if(_disposeAction != null)
_disposeAction();
}
}
For example:
using (new OnDisposed(() => Console.WriteLine("Dispose Called")))
{
Console.WriteLine("In using...");
}
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 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();
}
This is probably a dumb question but I'm going to ask it anyways... I am programing in C#.NET. I have a class that contains a non-static, instance EventHandler. Is it possible to trigger that EventHandler for every instance of the class that exists from a static method?? I know this is a long shot!
You can do this, but you'll need to create a static collection of all your objects:
public class Thing
{
public static List<Thing> _things = new List<Thing>();
public Thing()
{
_things.Add(this);
}
public static void SomeEventHandler(object value, EventHandler e)
{
foreach (Thing thing in _things)
{
// do something.
}
}
}
You'll want to watch out for accumulating too may "Things" . Make sure you remove them from the list when you don't need them anymore.
No, there isn't. Basically there's no way to find all instances of a class, unless you write your own code to do that.
EDIT: Intrigued as to why this is downvoted. Anyway, to add a bit more detail: you should avoid needing to do this. You could make your type implement IDisposable, then register against a static event handler in the constructor, and unregister in the Dispose method. Heck, you could even have a finalizer to do that for you, which will cost you performance but at least not leak if you fail to dispose of the instance.
All of these are somewhat grim options, however. It would be far better to try to redesign so as to avoid the requirement. Perhaps you can give us more information about what you're trying to do, and we can come up with a workaround?
I could be wrong in understanding what you mean, but it should be simple...
This is the main file
using System;
using IdeaClass;
namespace TestIdeas
{
class Program
{
static void Main(string[] args)
{
Ideas i = new Ideas();
Ideas.triggerMany();
Console.ReadLine();
}
}
}
Then there is the Ideas class:
using System;
namespace IdeaClass
{
public class Ideas
{
static OtherClass oc = new OtherClass();
public static void triggerMany()
{
oc.runThing("textual");
}
public Ideas()
{
Ideas.oc.ThingEvent += DoThingHandler;
}
public void DoThingHandler(string thing)
{
System.Console.WriteLine(thing);
}
}
}
And then the other class.
using System;
namespace IdeaClass
{
class OtherClass
{
public delegate void DoThing(string text);
public event DoThing ThingEvent;
public void runThing(string text)
{
if (ThingEvent != null)
{
ThingEvent(text);
}
}
}
}
It does cause unfortunate coupling between the class that raises the event and the class with the static call, but it seems to do what you want.
You can do like this :
public class MyClass{
private static List<MyClass> Instances = new List<MyClass>();
public MyClass(){
lock(typeof(MyClass)){
Instances.Add(this);
}
}}
After this you can do what ever you want with Instances.