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Object disposal guidance neededI'm a recent migrant from VB6 so I'm used to creating references to objects and then setting them to Nothing when they are no longer needed. Do I understand correctly that setting to Nothing is unnecessary in VB 2008 when the owning class or form is about to close anyway? Can disposal of objects always be left to the garbage collector, or are there times when setting to Nothing would be useful or desirable? Second, though related, question: when showing a form, using ..ShowDialog, I always call the form's .Dispose method on return. Should I set the form to Nothing as well? Everything seems to work whether I set to Nothing or not, but I can't tell whether resources are being retained unnecessarily. Thanks for any guidance. Gale. On 2010-04-04, Gale Green <g***@databeat.fsnet.co.uk> wrote:
Show quoteHide quote > Setting an local object to nothing is almost always useless - just as it was> Hi all. > > I'm a recent migrant from VB6 so I'm used to creating references to > objects and then setting them to Nothing when they are no longer > needed. > > Do I understand correctly that setting to Nothing is unnecessary in VB > 2008 when the owning class or form is about to close anyway? > > Can disposal of objects always be left to the garbage collector, or > are there times when setting to Nothing would be useful or desirable? > > Second, though related, question: when showing a form, using > .ShowDialog, I always call the form's .Dispose method on return. > Should I set the form to Nothing as well? Everything seems to work > whether I set to Nothing or not, but I can't tell whether resources > are being retained unnecessarily. > > Thanks for any guidance. > > Gale. in VB6 (except in very rare circumstances). About the only time setting an object to nothing is valuable is when it is a module or class level reference. The only time special handling is required is when an object implements the IDisposable interface. This is generally an indication that the object holds some resource (most often unmanaged) that needs cleanup. In those cases you will generally want to make sure that Dispose is called on the object when you are through with it. The easiest way to do this is to use Using... Using d As New MyDialog() If d.ShowDialog() = DialogResult.OK Then ' do cool stuff End If End Using The value of using is that it will ensure that Dispose is called on the object, even if an exception is thrown. It is bascially syntactic sugar for a Try/Finally block. There are objects that implement IDisposable that calling Dispose is not strictly necessary - such as DataSet. These objects actually end up with Dispose because they inherit from component. You may see advice from some that says to avoid calling dispose on these objects. I personally disagree with this advice for a number of reasons and suggest that you make it a strict rule to always call dispose if an object implments IDisposable. The reasons I disagree is because: 1) It makes the rules for Dispose more complicated - always call dispose except on object a, b, c, d. It's easier to remember, if an object implements IDisposable call dispose. 2) In OOP it is generally a bad idea to program to an objects implementation. As a rule, it is better to program to an Interface - and ignoring dispose on certain objects means you are programming against a known implementation details. This can leave your code broken if a future implementation changes... But, feel free to follow what ever rule you are most comfortable with... -- Tom Shelton On Sun, 04 Apr 2010 10:20:33 -0700, Tom Shelton
<tom_shel***@comcastXXXXXXX.net> wrote: > Good stuff. Thanks for all that Tom. All is now clear, and I agree with yourattitude to the Dispose method. Gale. However, in fact Tom does not call the Dispose method in 90% of the cases,
because he knows that those are implicitly called. Show quoteHide quote "Gale Green" <g***@databeat.fsnet.co.uk> wrote in message news:k8jhr5lsh37g7bu21era172b2i6ijera5p@4ax.com... > On Sun, 04 Apr 2010 10:20:33 -0700, Tom Shelton > <tom_shel***@comcastXXXXXXX.net> wrote: > >> Good stuff. > > Thanks for all that Tom. All is now clear, and I agree with your > attitude to the Dispose method. > > Gale. On 2010-04-05, Cor Ligthert[MVP] <Notmyfirstn***@planet.nl> wrote:
> However, in fact Tom does not call the Dispose method in 90% of the cases, Cor... It is true that I do not often call the Dispose method directly - > because he knows that those are implicitly called. > > I generally enclose disposable objects in a using block, which guarentees the call to dispose. The point that I was makeing is that I generally code to make sure that the object is disposed when I am done with it. I in fact, pointed this out in my post to the OP - the use of using. I am suggesting that the OP does likewise. Making sure a dispose call is made, implicitly via using, or explicitly amounts to about the same thing in my book. I wonder, did you have some valid point to make? -- Tom Shelton Yes I've a point, don't tell Wabash, it seems just to create a Trolling
thread, this is not the VB6 newsgroup. You wrote > There are objects that implement IDisposable that calling Dispose is not What you wrote, is the same reason why the OP was setting anything to > strictly necessary - such as DataSet. These objects actually end up with > Dispose because they inherit from component. You may see advice from some > that says to avoid calling dispose on these objects. I personally > disagree > with this advice for a number of reasons and suggest that you make it a > strict > rule to always call dispose if an object implments IDisposable. Nothing in VB6, somebody had written that and he took the chance that that one was right as the best. Now you tell him that he should change that practice to use on everything which implements Idisposable the "often" senseless dispose method, which only trashes often code in the same way as for ever using nothing in VB6. Form Closing label1.dispose Label2.dispose Label3.dispose Why don't you write that he should always count like this. Result = Cint(X.ToString) += 1 because every value type implements even an overloaded ToString method, so in your theory it must be used. All Forms controls and components implement the dispose method inherited from the Component class. You know likewise me that where calling the dispose is needed, this for forms and components is done implicit but since version 2005 hidden for most beginners in VB.Net in the designer part. You know also very well, that I am almost the only one who shows in the Microsoft Visual Basic forums samples with "using", so don't accuse me from things, which you know that aint true. You know how some regulars in this newsgroup disagree about this with you, while other of those agree, no problem but don't see it as a kind of evangelism to newbie's, who have set in past everything to nothing, just to take no risk and somebody wrote it. With every object which implements IDisposable, can be used with Using, so calling Dispose has no sense anymore, use the better code for that, it trashes at least not the code like I showed above. So where Dispose is needed it is better to use the Using keyword and if you don't know, you can also use that using keyword. Luckily the newer Classes don't implement IDisposale anymore so much anymore as in past. Your message could have also been without that sentence I quoted, it would have been a good and correct message. Now it seems at least to me more a little bit to kick some regulars here to the head. Cor Show quoteHide quote "Tom Shelton" <tom_shel***@comcastXXXXXXX.net> wrote in message news:#A0P71J1KHA.4204@TK2MSFTNGP04.phx.gbl... > On 2010-04-05, Cor Ligthert[MVP] <Notmyfirstn***@planet.nl> wrote: >> However, in fact Tom does not call the Dispose method in 90% of the >> cases, >> because he knows that those are implicitly called. >> >> > > Cor... It is true that I do not often call the Dispose method directly - > I generally enclose disposable objects in a using block, which guarentees > the > call to dispose. The point that I was makeing is that I generally code to > make sure that the object is disposed when I am done with it. I in fact, > pointed this out in my post to the OP - the use of using. I am suggesting > that the OP does likewise. Making sure a dispose call is made, implicitly > via > using, or explicitly amounts to about the same thing in my book. > > I wonder, did you have some valid point to make? > > -- > Tom Shelton Hmmm ,,,.........
to the OP This is discussed here manny times and it mostly indeed ends in a nothing saying thread http://www.developersdex.com/vb/message.asp?p=1121&r=6705983 http://bytes.com/topic/visual-basic-net/answers/444984-command-close-vs-command-dispose http://www.pcreview.co.uk/forums/thread-3854824-3.php etc etc etc etc etc etc http://www.google.nl/#hl=nl&source=hp&q=michel+posseth+dispose&meta=&aq=f&aqi=&aql=&oq=&gs_rfai=&fp=6bc54ad77a0995ae Read a few of them and try some of the examples i showed in these threads and you will notice that your program in some of my described situations can run forever while if you follow the Not call dispose camp in the same situation your progs will crash or degrade overall system performance . In case you are wondering ,, yes i am in the call dispose and set to nothing camp when it actually makes sense to do so , and if you are in doubt just do it, as it also doesn`t hurt while omitting it wil sure hurt your app. As i am a so called "Balena" programmer i follow his design patterns ( wich actually conform to MS standards as he is also the writer of the MS VB core reference guides ) described in the Core reference guides of Visual Basic ..Net and in these guide there are examples where a object pointer is set to nothing and it perfectly makes sence to do so , i have posted this example several times in the group so with the provided links you should find it :-) . Regards Michel Posseth Show quoteHide quote "Cor Ligthert[MVP]" <Notmyfirstn***@planet.nl> schreef in bericht news:eZVmWzK1KHA.6108@TK2MSFTNGP06.phx.gbl... > Yes I've a point, don't tell Wabash, it seems just to create a Trolling > thread, this is not the VB6 newsgroup. > > You wrote > > There are objects that implement IDisposable that calling Dispose is not >> strictly necessary - such as DataSet. These objects actually end up with >> Dispose because they inherit from component. You may see advice from >> some >> that says to avoid calling dispose on these objects. I personally >> disagree >> with this advice for a number of reasons and suggest that you make it a >> strict >> rule to always call dispose if an object implments IDisposable. > > What you wrote, is the same reason why the OP was setting anything to > Nothing in VB6, somebody had written that and he took the chance that that > one was right as the best. Now you tell him that he should change that > practice to use on everything which implements Idisposable the "often" > senseless dispose method, which only trashes often code in the same way as > for ever using nothing in VB6. > > Form Closing > label1.dispose > Label2.dispose > Label3.dispose > > Why don't you write that he should always count like this. > > Result = Cint(X.ToString) += 1 because every value type implements even an > overloaded ToString method, so in your theory it must be used. > > All Forms controls and components implement the dispose method inherited > from the Component class. > > You know likewise me that where calling the dispose is needed, this for > forms and components is done implicit but since version 2005 hidden for > most beginners in VB.Net in the designer part. > > You know also very well, that I am almost the only one who shows in the > Microsoft Visual Basic forums samples with "using", so don't accuse me > from things, which you know that aint true. > > You know how some regulars in this newsgroup disagree about this with you, > while other of those agree, no problem but don't see it as a kind of > evangelism to newbie's, who have set in past everything to nothing, just > to take no risk and somebody wrote it. > > With every object which implements IDisposable, can be used with Using, > so calling Dispose has no sense anymore, use the better code for that, it > trashes at least not the code like I showed above. > > So where Dispose is needed it is better to use the Using keyword and if > you don't know, you can also use that using keyword. > > Luckily the newer Classes don't implement IDisposale anymore so much > anymore as in past. > > Your message could have also been without that sentence I quoted, it would > have been a good and correct message. > > Now it seems at least to me more a little bit to kick some regulars here > to the head. > > Cor > > > > "Tom Shelton" <tom_shel***@comcastXXXXXXX.net> wrote in message > news:#A0P71J1KHA.4204@TK2MSFTNGP04.phx.gbl... >> On 2010-04-05, Cor Ligthert[MVP] <Notmyfirstn***@planet.nl> wrote: >>> However, in fact Tom does not call the Dispose method in 90% of the >>> cases, >>> because he knows that those are implicitly called. >>> >>> >> >> Cor... It is true that I do not often call the Dispose method directly - >> I generally enclose disposable objects in a using block, which guarentees >> the >> call to dispose. The point that I was makeing is that I generally code >> to >> make sure that the object is disposed when I am done with it. I in fact, >> pointed this out in my post to the OP - the use of using. I am >> suggesting >> that the OP does likewise. Making sure a dispose call is made, >> implicitly via >> using, or explicitly amounts to about the same thing in my book. >> >> I wonder, did you have some valid point to make? >> >> -- >> Tom Shelton > On Mon, 5 Apr 2010 13:15:11 +0200, "Michel Posseth [MCP]"
<m***@posseth.com> wrote: Thanks for all that, I shall have a read. I thought it was a fairly straightforward question - I never expected to start a thread going. Oh well. I shall have to get the Balena book - I used his VB book when I first started using VB6. Thanks again. Gale. Show quoteHide quote > >Hmmm ,,,......... > >to the OP > >This is discussed here manny times and it mostly indeed ends in a nothing >saying thread > >http://www.developersdex.com/vb/message.asp?p=1121&r=6705983 >http://bytes.com/topic/visual-basic-net/answers/444984-command-close-vs-command-dispose >http://www.pcreview.co.uk/forums/thread-3854824-3.php >etc etc etc etc etc etc > >http://www.google.nl/#hl=nl&source=hp&q=michel+posseth+dispose&meta=&aq=f&aqi=&aql=&oq=&gs_rfai=&fp=6bc54ad77a0995ae > >Read a few of them and try some of the examples i showed in these threads >and you will notice that your program in some of my described situations can >run forever >while if you follow the Not call dispose camp in the same situation your >progs will crash or degrade overall system performance . > >In case you are wondering ,, yes i am in the call dispose and set to nothing >camp when it actually makes sense to do so , and if you are in doubt just do >it, as it also doesn`t hurt while omitting it wil sure hurt your app. > >As i am a so called "Balena" programmer i follow his design patterns ( wich >actually conform to MS standards as he is also the writer of the MS VB core >reference guides ) described in the Core reference guides of Visual Basic >.Net and in these guide there are examples where a object pointer is set >to nothing and it perfectly makes sence to do so , i have posted this >example several times in the group so with the provided links you should >find it :-) . > >Regards > >Michel Posseth > > > > >"Cor Ligthert[MVP]" <Notmyfirstn***@planet.nl> schreef in bericht >news:eZVmWzK1KHA.6108@TK2MSFTNGP06.phx.gbl... >> Yes I've a point, don't tell Wabash, it seems just to create a Trolling >> thread, this is not the VB6 newsgroup. >> >> You wrote >> > There are objects that implement IDisposable that calling Dispose is not >>> strictly necessary - such as DataSet. These objects actually end up with >>> Dispose because they inherit from component. You may see advice from >>> some >>> that says to avoid calling dispose on these objects. I personally >>> disagree >>> with this advice for a number of reasons and suggest that you make it a >>> strict >>> rule to always call dispose if an object implments IDisposable. >> >> What you wrote, is the same reason why the OP was setting anything to >> Nothing in VB6, somebody had written that and he took the chance that that >> one was right as the best. Now you tell him that he should change that >> practice to use on everything which implements Idisposable the "often" >> senseless dispose method, which only trashes often code in the same way as >> for ever using nothing in VB6. >> >> Form Closing >> label1.dispose >> Label2.dispose >> Label3.dispose >> >> Why don't you write that he should always count like this. >> >> Result = Cint(X.ToString) += 1 because every value type implements even an >> overloaded ToString method, so in your theory it must be used. >> >> All Forms controls and components implement the dispose method inherited >> from the Component class. >> >> You know likewise me that where calling the dispose is needed, this for >> forms and components is done implicit but since version 2005 hidden for >> most beginners in VB.Net in the designer part. >> >> You know also very well, that I am almost the only one who shows in the >> Microsoft Visual Basic forums samples with "using", so don't accuse me >> from things, which you know that aint true. >> >> You know how some regulars in this newsgroup disagree about this with you, >> while other of those agree, no problem but don't see it as a kind of >> evangelism to newbie's, who have set in past everything to nothing, just >> to take no risk and somebody wrote it. >> >> With every object which implements IDisposable, can be used with Using, >> so calling Dispose has no sense anymore, use the better code for that, it >> trashes at least not the code like I showed above. >> >> So where Dispose is needed it is better to use the Using keyword and if >> you don't know, you can also use that using keyword. >> >> Luckily the newer Classes don't implement IDisposale anymore so much >> anymore as in past. >> >> Your message could have also been without that sentence I quoted, it would >> have been a good and correct message. >> >> Now it seems at least to me more a little bit to kick some regulars here >> to the head. >> >> Cor >> >> >> >> "Tom Shelton" <tom_shel***@comcastXXXXXXX.net> wrote in message >> news:#A0P71J1KHA.4204@TK2MSFTNGP04.phx.gbl... >>> On 2010-04-05, Cor Ligthert[MVP] <Notmyfirstn***@planet.nl> wrote: >>>> However, in fact Tom does not call the Dispose method in 90% of the >>>> cases, >>>> because he knows that those are implicitly called. >>>> >>>> >>> >>> Cor... It is true that I do not often call the Dispose method directly - >>> I generally enclose disposable objects in a using block, which guarentees >>> the >>> call to dispose. The point that I was makeing is that I generally code >>> to >>> make sure that the object is disposed when I am done with it. I in fact, >>> pointed this out in my post to the OP - the use of using. I am >>> suggesting >>> that the OP does likewise. Making sure a dispose call is made, >>> implicitly via >>> using, or explicitly amounts to about the same thing in my book. >>> >>> I wonder, did you have some valid point to make? >>> >>> -- >>> Tom Shelton >> On 2010-04-05, Cor Ligthert[MVP] <Notmyfirstn***@planet.nl> wrote:
Show quoteHide quote > Yes I've a point, don't tell Wabash, it seems just to create a Trolling And as always, we disagree on this point (and despite your inferences, you are> thread, this is not the VB6 newsgroup. > > You wrote > > There are objects that implement IDisposable that calling Dispose is not >> strictly necessary - such as DataSet. These objects actually end up with >> Dispose because they inherit from component. You may see advice from some >> that says to avoid calling dispose on these objects. I personally >> disagree >> with this advice for a number of reasons and suggest that you make it a >> strict >> rule to always call dispose if an object implments IDisposable. > > What you wrote, is the same reason why the OP was setting anything to > Nothing in VB6, somebody had written that and he took the chance that that > one was right as the best. Now you tell him that he should change that > practice to use on everything which implements Idisposable the "often" > senseless dispose method, which only trashes often code in the same way as > for ever using nothing in VB6. > almost the only one I know who does). I see you once again bring in a long set of unrelated arguments. I will ignore the rest of your post, and just try to make sure my position is clear. Integer.ToString(): Totally irelavent. I am in no way saying that every method of an object must be called simply because it exits. IDisposable is part of a resource management pattern. The presence of IDisposable is supposed to signal to the developer using the object that this class potentially contains resources that should be released as early as possible. As such, it should be called when you are done with the object. Now, I treat controls and components that are sited on forms a bit differently, because the system generates the code to dispose of these. In other words, the parent forms dispose method disposes all of it's children. So, using a dialog: Using dlg As New MyDlg If dlg.ShowDialog() = DialogResult.OK Then ... End If End Using Is sufficent to dispose the form and all of it's children. So, with the exception of the main form - since that object lives the entire life of the program, it's a pretty safe bet that I am making sure a call to dispose is made. Other objects, that maybe used as local values, ect that implement Dispose are almost always wrapped in a using block - so I very rarely call Dispose directly. And yes, I do advocate the use of a using with classes such as dataset, memorystream, etc. The main reason is that I like to keep rules simple and consistant. And, I don't believe in programming to an object's implementation. Just because I've looked, and I know a memorystream holds no unmanaged resources - it's simply wrapper for a byte array, I still wrap it in a using block. Why? Because I try to program to interfaces and not implementations. It implements IDisposable, that is an interface with a special meaning - so I follow the contract. -- Tom Shelton <Snipped quote from Tom>
> And as always, we disagree on this point (and despite your inferences, you There is a guy here already a while active with the name Armin Zingler,> are > almost the only one I know who does). I see you once again bring in a > long set of unrelated arguments. I will ignore the rest of your post, and > just try to make sure my position is clear. > It is of course possible you've never seen any post from him. He has in this no other opinion than me. Another guy, Herfried Wagner. Ever seen a post from him? The same. In past; somebody who changed his opinion and then told the same like me, Jay B. Harlow. A pity that you've never seen any post from them about dispose. If you had read my last post in this thread, you would have seen, that I am not discussing the use of using. I assume that I am making more propaganda (at least in quantity) for that then you. However, in my idea is therefore the use of the dispose method a proof of non well formed code. Cor Am 05.04.2010 19:18, schrieb Cor Ligthert[MVP]:
>> I'm not really getting your point mentioning my name, but I was about to> There is a guy here already a while active with the name Armin Zingler, reply to Tom's message and say that I 100% agree with him. Despite, let's stay friends. ;) -- Armin The last one or the first one in which he writes that dispose should always
be used? The last one is completely different from the first one, and I am writing about his first one, where he tells he is a follower from those who write. They did not put for nothing the Idisposable interface on those classes. It is a contract so it should be used. I was not aware it was your opinion, but glad to know. Maybe you wont believe, but then I don't agree that with you. :-) CorShow quoteHide quote "Armin Zingler" <az.nospam@freenet.de> wrote in message news:#FL2koO1KHA.3412@TK2MSFTNGP05.phx.gbl... > Am 05.04.2010 19:18, schrieb Cor Ligthert[MVP]: >>> >> There is a guy here already a while active with the name Armin Zingler, > > I'm not really getting your point mentioning my name, but I was about to > reply to Tom's message and say that I 100% agree with him. > > Despite, let's stay friends. ;) > > -- > Armin Am 05.04.2010 20:36, schrieb Cor Ligthert[MVP]:
> The last one or the first one in which he writes that dispose should always I read them again but I don't see a contradiction.> be used? > > The last one is completely different from the first one, and I am writing > about his first one, where he tells he is a follower from those who write. > They did not put for nothing the Idisposable interface on those classes. It yes, should be used.> is a contract so it should be used. > I was not aware it was your opinion, but glad to know. Maybe you wont Maybe it's all a big misunderstanding?!> believe, but then I don't agree that with you. > > :-) -- Armin > Maybe it's all a big misunderstanding?! Yea, good words Armin, I hope so.> Cor 
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