I'm getting confused about all this talk about IDispose and "using" Statements. I wonder if someone can tell me if I need to use either a "using" Statement or some sort of implementation of IDispose in the following test example...
public class Main()
{
MyFile myFile = new MyFile("c:\subdir\subdir2\testFile.txt");
Console.Writeline("File Name: " + myFile.FileName() + "File Size: " + myFile.FileSize());
}
public class MyFile
{
private FileInfo _fInfo;
public MyFile(string fullFilePath)
{
_fInfo = new FileInfo(fullFilePath);
}
public string FileName()
{
return _fInfo.Name;
}
public long FileSize()
{
return _fInfo.Length;
}
}
No, your example doesn't use any resources which need disposing (it doesn't touch anything which implements IDisposable, or have any direct handles to unmanaged resources) so you don't need to implement IDisposable.
Now if you changed your class to open the file, and maintain a FileStream field referring to the open file handle, then it would make sense to implement IDisposable to close the stream.
No, in the code provided I don't see any resource used that have to be disposed. So the answer is no, do not use in this code it.
In your example there is nothing to dispose, so you have no need to do that.
If you want to read/write in file you can use Streamreader/Streamwriter for that and in that way you will need to dispose that objects after using them.
using(StreamReader sreader=new StreamReader())
{
//your code
}
So in this case using statement will help you to don't think about manually disposing/closing your object/
In your code there is no need for any Dispose / using - for a definitive guide on IDisposable see here.
Related
Seeking best inputs on correct usage of C# using statement. Can I use using statement on a parameter object as in the following uncommon example code snippet (viz., multi-layer application)?
Although the code snippet is different from what I feel that the using statement should be in ProcessFileAndReturnNumberFromStream() method of 'Business' class.
Why is it an uncommon practice to use using statement on object passed via parameter? Please correct or elaborate on the flaw?
using System;
using System.IO;
class Data
{
public double? GetNumberFromStream(StreamReader sr)
{
double? number;
try
{
using (sr)
{
number = Convert.ToDouble(sr.ReadToEnd());
return number;
}
}
finally
{
number = null;
}
}
}
class Business
{
public double? ProcessFileAndReturnNumberFromStream()
{
string fileName = "Test.txt";
StreamReader sr = new StreamReader(fileName);
Data dat = new Data();
return dat.GetNumberFromStream(sr);
}
}
class GUI
{
static void Main()
{
Business bus = new Business();
double? number = bus.ProcessFileAndReturnNumberFromStream();
Console.WriteLine(number);
Console.ReadKey();
}
}
Please help.
Thanks
If a method is passed an object that implements IDisposable, it's usually the responsibility of the caller to manage the lifetime of that object, rather than the callee.
public double? ProcessFileAndReturnNumberFromStream()
{
string fileName = "Test.txt";
Data dat = new Data();
using (StreamReader sr = new StreamReader(fileName))
{
return dat.GetNumberFromStream(sr);
}
}
The caller that is passing the instance of IDisposable should be the one to use the using statement. If the callee uses it, the object will be disposed while outside the immediate control of the caller who 'owns' the object.
Can I use using statement on a parameter object as in the following uncommon example code snippet (viz., multi-layer application)?
You can, but it's generally odd to do so. Usually whatever is creating the StreamReader would be expecting to "own" it and dispose of it when they're done with it. It would be more usual for your ProcessFileAndReturnNumberFromStream method to be:
using (StreamReader sr = new StreamReader(fileName))
{
Data dat = new Data();
return dat.GetNumberFromStream(sr);
}
(Although I'd personally use File.OpenText instead of explicitly constructing the StreamReader.)
Your GetNumberFromStream method would then not need the using statement. It also doesn't need the try/finally block at all - it's an odd implementation all round, given that it will never return null, either...
It's also odd that you're creating a new instance of Data and then doing nothing with it - as your GetNumberFromStream method doesn't use an instance variables or override a base class method, you should consider making it static.
Such API would be extremely troublesome.
You would never know whether or not the object passed to a method is disposed inside the method or not. Thus, if this is you who create the object and pass it there, you would also never know whether or not you should dispose the object you have just created and passed to the method or not.
I guess then, while this is technically possible, it would promote the bad programming style.
Where to dispose StreamWriter if I need it during entire application lifetime? I'm going to dispose it in destructor, will that work? I have to dispose to flush data, and I don't want to use AutoFlush feature because from msdn: "You can get better performance by setting AutoFlush to false, assuming that you always call Close (or at least Flush) when you're done writing with a StreamWriter."
So should i Dispose in destructor like in the code below?
class Log
{
private static StreamWriter swLog = new StreamWriter("logMAIN.txt");
static ~Log()
{
swLog.Dispose();
}
public static void Push(LogItemType type, string message)
{
swLog.WriteLine(type + " " + DateTime.Now.TimeOfDay + " " + message);
}
}
upd instead of Dispose i meant to call Close but it is not improtant in this case because they seems doing exactly the same.
You seem to be basing your decision not to flush on some performance information from MSDN. That's not where I'd start.
Do you have evidence that using AutoFlush causes you significant performance problems?
Have you considered alleviating these performance problems in a different way, e.g. having a single thread writing to the StreamWriter, either auto-flushing or periodically flushing every 20 seconds or whatever?
You haven't told us what kind of application you're writing, mind you - that can make a significant difference in terms of how much you know about shutdown.
Also note that the code you've given isn't thread-safe to start with. You could end up using the StreamWriter from multiple threads concurrently; I doubt that StreamWriter is particularly designed for that scenario.
The problem really is the way the StreamWriter is initialized. Using a regular object like this
using (var logger = new Log())
{
app.Run();
}
The StreamWriter can still be a static field in the Log class, but is initialized and disposed at known points in time rather than using a static initializer.
For this to work you will need to let you log class implement the IDisposable interface and dispose the StreamWriter in the Dispose method like this:
class Log: IDisposable
{
private static StreamWriter swLog;
public Log()
{
swLog = new StreamWriter("logMAIN.txt");
}
public void Dispose()
{
swLog.Dispose();
}
public static void Push(LogItemType type, string message)
{
swLog.WriteLine(type + " " + DateTime.Now.TimeOfDay + " " + message);
}
}
Also note how the Log will be disposed even if an exception is thrown.
Possible Duplicate:
Should I Dispose() DataSet and DataTable?
OP comment: I would like to say that the "Should I Dispose() DataSet and DataTable?" link isn't a possible solution. It's a good link, but this is more design related. Instead, ignore that the exposed property is a DataSet and replace it with something that should be disposed. The same question would apply there.
I'm messing around with Crystal Reports, and I have a "ReportData" class. In other words, this class encapsulates the "Filling" of the DataSet I will use.
public class ReportData
{
private DataSet1 m_DS = null; // Notice this disposable member variable
public ReportData( ... some parameters ...)
{
m_DS = new DataSet1();
// Plus some other manipulation on m_DS
}
public DataSet1 GetDataSet
{
get
{
return m_DS;
}
}
// Everything else is pretty much private.
// This class is here to generate my DataSet
}
Here is how it would be used by some other class:
private void SetReportDataSource()
{
DataSet1 ds = m_RptData.GetDataSet;
m_Rpt.SetDataSource(ds);
}
I'm pretty much learning C# on the fly (read a couple of chapters in an intro book, and just went at it, googling everything along the way). From what I understand, if it implements IDisposable, you better Dispose it. A DataSet implements IDisposable, so we need to Dispose it.
Here's where the design part comes in:
Question 1a: Do I make my ReportData class IDisposable?
In other words, it looks like I could just do this and be done with it:
private void SetReportDataSource()
{
using (DataSet1 ds = m_RptData.GetDataSet)
{
m_Rpt.SetDataSource(ds);
}
}
Question 1b: Should I be more defensive in some way?
I don't know, I guess I'm really, really trying to ensure that it gets disposed. For example, taking my SetReportDatsSource function as an example. I used "using", but someone else may use the class and forget to add the using or call Dispose in some way. Therefore, I go to my ReportData class:
public class ReportData : IDisposable
{
private DataSet1 m_DS = null; // Notice this disposable member variable
private bool m_IsDisposed = false; // This is new!
public ReportData( ... some parameters ...)
{
m_DS = new DataSet1();
// Plus some other manipulation on m_DS
}
// New code here (up until the GetDataSet property)
~ReportData()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (m_IsDisposed == true)
{
return;
}
if (m_DS != null)
{
m_DS.Dispose();
m_DS = null;
}
m_IsDisposed = true;
}
// Done with new code
public DataSet1 GetDataSet
{
get
{
return m_DS;
}
}
// Everything else is pretty much private.
// This class is here to generate my DataSet
}
Now, let's go back to the calling class, we still have:
private void SetReportDataSource()
{
using (DataSet1 ds = m_RptData.GetDataSet)
{
m_Rpt.SetDataSource(ds);
}
}
But, I made ReportData (m_RptData) disposable now too! So, we are going to want to dispose of that! And because it's a member variable (and I can't just use "using" in the way I'm using it with SetReportDataSource), you start thinking about making this calling class IDisposable, so I can have:
protected virtual void Dispose(bool disposing)
{
if (m_IsDisposed == true)
{
return;
}
if (m_ReportData != null)
{
m_ReportData.Dispose();
m_ReportData = null;
}
m_IsDisposed = true;
}
So, now this class has the destructor/finalizer and its public Dispose method, disposing of ReportData. We're guaranteed that we dispose of the DataSet!
But then again, this will result in DataSet's Dispose method getting called twice. Because the SetReportDataSource function disposes the exposed DataSet, and the ReportData class is also disposing the same thing (and there is not an easy way to determine if someone disposed of the exposed DataSet).
Seems kind of nutty. It looks like to me that I:
a) May be overthinking this (or just trying to be really defensive, which is good)!
b) Might be jumping through a bunch of hoops.
Maybe the rule should be: If my class is going to expose it, the calling function should be responsible for disposing it.
The only issue I see with that (and that's why I posted here):
In between the time that ReportData member variable is instantiated, and SetReportDataSource is called, some error/exception may occur. So, we never get a chance to do the "using" (inside of SetReportDataSource) on our DataSet. But that dataset was constructed with ReportData (and we want to call dispose on it!)
So, now we're back to making ReportData IDisposable, because we are going to at least need some public "CleanUp" function ... ok, I'm done. :)
If you are holding onto something that implements IDisposable, the simplest pattern is to implement IDisposable yourself, and call the Dispose methods on all IDisposables you own. Being more defensive than doesn't seem feasible; if somebody using your class forgets to call your Dispose method, then how do you ever know they are done using you?
Edit: On second thoughts, a Finalize call tells you that your client is done using you; they have no more references to you...
Please see: Should I Dispose() DataSet and DataTable?
As has come up several times on SO, if an object it implements IDisposable then you should call Dispose(). [There are a few places in the .NET framework where the original designers, presumably thouight they would require Dispose() but then didn't need it. But the safest and correct thing to do would be to call Dispose regardless.]
You don't show the code for SetDataSource but this piece of code is only going to work if SetDataSource immediately consumes the contents of the DataSet and does not store a reference to it:
private void SetReportDataSource()
{
using (DataSet1 ds = m_RptData.GetDataSet)
{
m_Rpt.SetDataSource(ds);
}
}
As for the rest of your code and question (quoting a deleted answer):
you don't have anything that needs to be finalized. You might have noticed that when you found out that you had no use for the disposing argument. All you need is this:
void Dispose() {
if (m_DS != null) m_DS.Dispose()
}
The general rule for Finalizers is: When in doubt, Don't.
You will only need one when you directly use an unmanaged resource.
Answer 1A: I would recommend the using syntax, the reason for that is it seems to be the standard for handling things of this nature.
Answer 1B: If someone else is using your class, I assume you mean extending, it is on the implementer to handle any changes he sees fit. According to the docs on Dispose()
If an object's Dispose method is called more than once, the object must ignore all calls after the first one. The object must not throw an exception if its Dispose method is called multiple times. Dispose can throw an exception if an error occurs because a resource has already been freed and Dispose had not been called previously. (http://msdn.microsoft.com/en-us/library/system.idisposable.dispose%28VS.71%29.aspx)
The garbage collector will at some point get a hold of your object and handle it. Barring catastrophe.
This question already has answers here:
Closed 13 years ago.
I see loads of code snippets with the following Syntax
using (RandomType variable = new RandomType(1,2,3))
{
// A bunch of code here.
}
why not just declare the variable and use it?
This Using syntax seems to just clutter the code and make it less readable. And if it's so important that that varible is only available in that scope why not just put that block in a function?
Using has a very distinct purpose.
It is designed for use with types that implement IDisposable.
In your case, if RandomType implements IDisposable, it will get .Dispose()'d at the end of the block.
using (RandomType variable = new RandomType(1,2,3))
{
// A bunch of code here.
}
is pretty much the same (with a few subtle differences) as:
RandomType variable = new RandomType(1,2,3);
try
{
// A bunch of code
}
finally
{
if(variable != null)
variable.Dispose()
}
Note that when calling "Using", you can cast anything as IDisposable:
using(RandomType as IDisposable)
The null check in the finally will catch anything that doesn't actually implement IDisposable.
No, it does not clutter your code , or make it less readable.
A using statement can only be used on IDisposable types (that is, types that implement IDisposable).
By using that type in a using - block, the Dispose method of that type will be used when the scope of the using-block ends.
So, tell me which code is less readable for you:
using( SomeType t = new SomeType() )
{
// do some stuff
}
or
SomeType t = new SomeType();
try
{
// do some stuff
}
finally
{
if( t != null )
{
t.Dispose();
}
}
An object being used in a using statement must implement IDisposable, so at the end of the scope, you're guaranteed that Dispose() will be called, so theoretically, your object should be released at that point. In some cases, I've found it makes my code clearer.
The using keyword provides a deterministic way to clean up the managed or unmanaged resources that an object allocates. If you don't use the using keyword, you are responsible to call Dispose() (or in some cases, Close()) when finished with that object. Otherwise, the resources may not be cleaned up until the next garbage collection, or even not at all.
According to MSDN, the following using code:
using (Font font1 = new Font("Arial", 10.0f))
{
byte charset = font1.GdiCharSet;
}
expands to this:
{
Font font1 = new Font("Arial", 10.0f);
try
{
byte charset = font1.GdiCharSet;
}
finally
{
if (font1 != null)
((IDisposable)font1).Dispose();
}
}
And it does really not clutter your code. Quite the opposite actually!
I was reading another answer. And it made me wonder, when do does one need to explicitly call Dispose if I am using using statements?
EDIT:
Just to vindicate myself from being a total know-nothing, the reason I asked was because someone on another thread said something implying there was a good reason to have to call Dispose manually... So I figured, why not ask about it?
You don't. The using statement does it for you.
According to MSDN, this code example:
using (Font font1 = new Font("Arial", 10.0f))
{
byte charset = font1.GdiCharSet;
}
is expanded, when compiled, to the following code (note the extra curly braces to create the limited scope for the object):
{
Font font1 = new Font("Arial", 10.0f);
try
{
byte charset = font1.GdiCharSet;
}
finally
{
if (font1 != null)
((IDisposable)font1).Dispose();
}
}
Note: As #timvw mentioned, if you chain methods or use object initializers in the using statement itself and an exception is thrown, the object won't be disposed. Which makes sense if you look at what it will be expanded to. For example:
using(var cat = new Cat().AsDog())
{
// Pretend a cat is a dog
}
expands to
{
var cat = new Cat().AsDog(); // Throws
try
{
// Never reached
}
finally
{
if (cat != null)
((IDisposable)cat).Dispose();
}
}
AsDog will obviously throw an exception, since a cat can never be as awesome as a dog. The cat will then never be disposed of. Of course, some people may argue that cats should never be disposed of, but that's another discussion...
Anyways, just make sure that what you do using( here ) is safe and you are good to go. (Obviously, if the constructor fails, the object won't be created to begin with, so no need to dispose).
Normally you don't. This is the point of the using statement. There is however a situation where you have to be careful:
If you reassign the variable to another value the using statement will only call the Dispose method on the original value.
using (someValue = new DisposableObject())
{
someValue = someOtherValue;
}
The compiler will even give you a Warning about this:
Possibly incorrect assignment to local 'someValue' which is the argument to a using or lock statement. The Dispose call or unlocking will happen on the original value of the local.
Be careful when using c# 3.0 object initializers though. An example can be found here: http://ayende.com/Blog/archive/2009/01/15/avoid-object-initializers-amp-the-using-statement.aspx
Never. It will call Dispose once the statements inside using blocks finish execution.
The whole point of the using statement is that if your object implements IDisposable, the dipose will be called at the end of the code block. That's what it's there for, to do it automaticaly for you.
As far as i know
using (var myDisposable = new MyDisposable())
{
...
}
is basically translated by the compiler to
var myDisposable = new MyDisposable()
try
{
...
}
finally
{
myDisposable.Dispose();
}