|
Hi All,
Can anyone please clarify my dout about IDisposable intreface in C#.
We all know tat IDisposable interface is using for disposing unmanaged resources.
I have a class which contains following code. here i have implimented the Dispose method from IDisposable interface.
class ClassA:IDisposable
{
public ClassA()
{
Console.WriteLine("ClassBeingTested: Constructor");
}
private bool disposed = false;
Image img = null;
public Image Image
{
get { return img; }
}
~ClassA()
{
Console.WriteLine("ClassBeingTested: Destructor");
// call Dispose with false. Since we're in the
// destructor call, the managed resources will be
// disposed of anyways.
Dispose(false);
}
public void Dispose()
{
Console.WriteLine("ClassBeingTested: Dispose");
// dispose of the managed and unmanaged resources
Dispose(true);
// tell the GC that the Finalize process no longer needs
// to be run for this object.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposeManagedResources)
{
// process only if mananged and unmanaged resources have
// not been disposed of.
if (!this.disposed)
{
Console.WriteLine("ClassBeingTested: Resources not disposed");
if (disposeManagedResources)
{
Console.WriteLine("ClassBeingTested: Disposing managed resources");
// dispose managed resources
if (img != null)
{
img.Dispose();
img = null;
}
}
// dispose unmanaged resources
Console.WriteLine("ClassBeingTested: Disposing unmanaged resouces");
disposed = true;
}
else
{
Console.WriteLine("ClassBeingTested: Resources already disposed");
}
}
// loading an image
public void LoadImage(string file)
{
Console.WriteLine("ClassBeingTested: LoadImage");
img = Image.FromFile(file);
}
}
What my doubt is why i need to impliment the Dispose method from IDisposable interface?. Instead of that i can create my own Dispose method in my class without inheriting from IDisposable interface which i have given below.
for the class below i haven't inherited my class from IDisposable interface. instead of that i created my own dispose method. this also works fine.
class ClassA
{
public ClassA()
{
Console.WriteLine("ClassBeingTested: Constructor");
}
private bool disposed = false;
Image img = null;
public Image Image
{
get { return img; }
}
~ClassA()
{
Console.WriteLine("ClassBeingTested: Destructor");
// call Dispose with false. Since we're in the
// destructor call, the managed resources will be
// disposed of anyways.
Dispose(false);
}
public void Dispose()
{
Console.WriteLine("ClassBeingTested: Dispose");
// dispose of the managed and unmanaged resources
Dispose(true);
// tell the GC that the Finalize process no longer needs
// to be run for this object.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposeManagedResources)
{
// process only if mananged and unmanaged resources have
// not been disposed of.
if (!this.disposed)
{
Console.WriteLine("ClassBeingTested: Resources not disposed");
if (disposeManagedResources)
{
Console.WriteLine("ClassBeingTested: Disposing managed resources");
// dispose managed resources
if (img != null)
{
img.Dispose();
img = null;
}
}
// dispose unmanaged resources
Console.WriteLine("ClassBeingTested: Disposing unmanaged resouces");
disposed = true;
}
else
{
Console.WriteLine("ClassBeingTested: Resources already disposed");
}
}
// loading an image
public void LoadImage(string file)
{
Console.WriteLine("ClassBeingTested: LoadImage");
img = Image.FromFile(file);
}
}
So can any one tel me tat the reason behind of implimenting dispose method from IDisposable interface. I think everybody understands my question. i searched in google a lot. but i did not get a proper answer.So please clarify my doubt.
Regards
Lijo
|
|
|
|
|
As you pointed out yourself, it makes sense to implement IDisposable to free up unmanaged resources. Since this class embeds an Image, which is IDisposable, it should itself be disposable. I didn't read all of the lenghty unformatted code you posted, but if that's all there is to it, it would suffice to do this:
public void Dispose()
{
if (img != null) img.Dispose();
}
|
|
|
|
|
Thats fine. There is nothing relevant in my code. Code i have given just for explaining my Problem.
So Can u please tell me why should i inherit my class from IDisposable intreface for implementing dispose method? Here i can write my own Dispose method without inheriting IDisposable intreface which i have shown in my code. Then can u please tell me why microsoft is telling that i have to inherit my class from IDisposable intreface for implimenting dispose method? is there any specific reason behind that?
in my code directly i used img.Dispose();. here i no need to inherit my class from IDisposable intreface.
I think u can understand what i am trying to clarify..
Regards
Lijo
|
|
|
|
|
Once i used interface for a plugin.
If you use unmanaged calss, you need to close window handles and other stuff. The IDisposable interface exsist for GarbageColletor that can properly dispose a class. This apply to automatic Dispose. Not call from a code
|
|
|
|
|
I think u guys did not understand my question. i very well know tat we have to use IDisposable intreface for handiling un managed resources. but we no need to inherit our class from IDisposable intreface for implimenting Dispose method. I can write my own Dispose method. So my question is what is the specific reason behind inheriting our class from IDisposable intreface?
|
|
|
|
|
This is from MSDN:
The primary use of this interface is to release unmanaged resources. The garbage collector automatically releases the memory allocated to a managed object when that object is no longer used. However, it is not possible to predict when garbage collection will occur. Furthermore, the garbage collector has no knowledge of unmanaged resources such as window handles, or open files and streams.
In other words if you implement your own Dispose without implementing IDisposable interface, Garbage collector won't be able to call Dispose method. If you call manualy Dispose method it does not hurt system. If you do not implement IDisposable iterface and you do not call Dispose method, Garbage Collector will not call Dispose, so any unmanaged handles will remain even after the process was closed or killed. I suggest you Implement it, because it doesn't hurt to have it
|
|
|
|
|
Sorry for the delay in responding - I forgot about it.
1) It tells the user of the class that instances should be disposed.
A programmer familiar with .NET will immediately recognize and understand what pattern is involved and the reasons for it just by glancing at the class declaration.
2) It allows code to test programmatically if an object is disposable and to invoke the logic without knowledge of it's type.
if (obj is IDisposable) ((IDisposable)obj).Dispose();
3) It allows encapsulation of the object's resources.
In your case, and in many cases, you may need to expose the image to outside users (rather than clone the internal resource and return a copy). But in general, a class should be responsible for managing all the state belonging to it. Following this guideline greatly simplifies life even if you cannot always *enforce* it by fully encapsulating state.
4) It allows the user to easily ensure instances are in fact disposed, whether or not exceptions occur, since several CLS-compliant languages (including C# and VB.NET) have special statements for this exact purpose. In C#,
using (var x = new MyThing())
{
... code block ...
}
var x = new MyThing();
try
{
... code block ...
}
finally
{
if (x != null) x.Dispose();
}
All of these are, in my opinion, important reasons for implementing IDisposable when the object is in fact disposable. Having x.img.Dispose() violates established OOP practice (and there are good reasons for that practice).
|
|
|
|
|
If you did not implement from IDisposable, you wouldn't be able to use the using construct to automatically dispose your object - you'd have to take care of it yourself. Effectively, the using construct turns the code into a try/finally block where Dispose is called in the finally portion - it uses a cast to IDisposable to ensure that it can do this. Consider the following sample:
public class MyBaseClass
{
public virtual void Dispose()
{}
}
public class MyDisposableBaseClass : MyBaseClass, IDisposable
{
}
using (MyBaseClass myClass = new MyDisposableBaseClass())
{
}
using (MyDisposableBaseClass myClass = new MyDisposableBaseClass())
{
}As you can see, even though MyBaseClass has a Dispose method, you can't use it in a using block for disposal.
"WPF has many lovers. It's a veritable porn star!" - Josh Smith As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.
My blog | My articles | MoXAML PowerToys | Onyx
|
|
|
|
|
Along with what Pete said in the above reply about the using construct, implementing IDisposable helps automatic tools detect potential memory leaks. In your example, your class contains a disposable object. If the dispose method on your class never gets called, the image will not be disposed and the unmanaged resource will leak. When you implement IDisposable, tools have a better chance of detecting such leaks.
As an aside, you should not have a class finalizer (the ~A()) method unless you directly own an unmanaged resource such as a file handle stored as an IntPtr. The IDisposable classes you own as fields will have their own finalizer to take care of the unmanaged resources. Having unnecessary finalizers decreases the efficiency of the garbage collector.
|
|
|
|
|
Gideon Engelberth wrote: As an aside, you should not have a class finalizer (the ~A()) method unless you directly own an unmanaged resource such as a file handle stored as an IntPtr. The IDisposable classes you own as fields will have their own finalizer to take care of the unmanaged resources. Having unnecessary finalizers decreases the efficiency of the garbage collector.
I agree mainly as it is a valid information, but he get's around this problem, as he is using:
GC.SuppressFinalize(this);
By calling the "SuppressFinalize", the GC will not move the object to the finalization queue, and so prefent the double lookup of the object.
All the best,
Martin
|
|
|
|
|
He does, but only when the user has called Dispose. And since the class didn't implement IDisposable there is a higher probability that objects would not have been disposed. (At least where I've worked there tend to be plenty of programmers who fail to include try-finally blocks where necessary for correctness, as they (I believe) work based on the idea that if it runs OK on their machine this means the code is "correct" - a notion it would be useful to disspell from our profession imho.)
|
|
|
|
|
dojohansen wrote: And since the class didn't implement IDisposable there is a higher probability that objects would not have been disposed.
Second that! I wouldn't like to see such an implementation in my projects as it makes no sence not to implement IDisposable.
I just wanted to point to the "SuppressFinalize", also for the cases were you have to worry about your unmanaged recources.
All the best,
Martin
|
|
|
|
|
That's the main hit, but there is still a small hit from the fact that it has to be put on the finalization list in the first place (and then taken back off in Dispose). I have no idea how big that hit is, since that will depend mostly on how many of these objects are being created.
|
|
|
|
|
How can I get a single character without pressing enter in C#, something like _getch in C++? Tried with Console.Read, but still have to press enter to continue.
|
|
|
|
|
Have you tried Console.ReadKey()?
Life is a stage and we are all actors!
|
|
|
|
|
How I can get value of tag <!-- Hi World --> by C# codes.
I have used this code but it gives me error !
Code :
string b = node.SelectSingleNode("<!--").InnerText;
<code></code>error : Expression must evaluate to a node-set.
I can get <value>dsf and and <comment> with this code.
string a = node.SelectSingleNode("comment").InnerText;
|
|
|
|
|
Hi,
the selectSingleNode-method expects a string containing a xpath-expression. See here:
<a href="http://msdn.microsoft.com/en-us/library/h0hw012b%28VS.80%29.aspx">http://msdn.microsoft.com/en-us/library/h0hw012b%28VS.80%29.aspx</a>[<a href="http://msdn.microsoft.com/en-us/library/h0hw012b%28VS.80%29.aspx" target="_blank" title="New Window">^</a>]
So the second line you posted is a correct xpath-expression.
So with this xpath-expression:
<code>
/mynode/comment()
</code>
you select all comments within the node mynode. To access the first comment use:
<code>
/mynode/comment()[1]
</code>
This should do the trick.
Regards
Sebastian
|
|
|
|
|
Sorry I didnt get your idea
how can i get the value of
would you explaine more.....
in my Resource file i have this tags
<value>Ok
<comment>button Ok
<value>0,0
<comment>button Ok
<value>75, 23
<comment>button Ok
|
|
|
|
|
Is this an xml-file? Okay let us assume your file looks like this:
<br />
<resources><br />
<item><br />
<tag1>OK</tag1><br />
<tag2>button OK</tag2><br />
<!-- button2 --><br />
</item><br />
<item><br />
<tag1>0,0</tag1><br />
<tag2>button OK</tag2><br />
<!-- button2 --><br />
</item><br />
<item><br />
<tag1>75,23</tag1><br />
<tag2>button OK</tag2><br />
<!-- button2 --><br />
</item><br />
</resources><br />
Then you can get the first comment with (with itemNode is set to the first node with the tag item):
<br />
string b = itemNode.SelectSingleNode("./comment()[1]").InnerText<br />
Does this help you?
Regards
Sebastian
|
|
|
|
|
Thanks a Lot !!!!!!!!!!!!!!!
  ![Rose | [Rose]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/rose.gif)   
it was great help to me
|
|
|
|
|
You can't get this value as far as I know. You can put this value in a hidden label, than get this value.
modified 27-May-14 5:05am.
|
|
|
|
|
Hello,
I have a problem:
I want to draw a line between object A (Say an ellipse) and object B (also an ellipse). Now, between those object lies object C (which is a triangle). Now how can I draw the shortest line between A and B avoiding object C, using GDI+?
Thanks in advance,
Zaegra
Motivation is the key to software development.
|
|
|
|
|
In two steps:
1) Solve the mathmatical formula to determine the line's endpoints
2) Draw the line
I can't tell from your question which of the two steps you need help with, but it seems like you are asking for help with step 1. If you already know how to do step 2, then this is the wrong forum to ask your question as part 1 is not C# related.
Sounds like somebody's got a case of the Mondays
-Jeff
|
|
|
|
|
I have a datatable(code behind datatable class) that contains a column with the name aa which have ulphanumeric values.
Is there any way to find those rows having numeric values onlywithout doing iteration ?
|
|
|
|
|
The Select method of the DataTable class allows you to do just that, using pseudo T-SQL.
It returns an array of DataRow.
E.g.:
DataRow[] results = yourDataTable.Select("aa=15");
var question = (_2b || !(_2b));
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
