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The reason is that you have declared c outside the using statement.
The Dispose method is called by the Garbage Collector when collecting objects that are not longer referenced. Because you are still holding a reference to c after leaving the using block, the GC does not collect c and consequently Dispose is called only when Main goes out of scope.
But even if you had declared c within the using statement, you are not garantueed to see the expected order of events - the GC is invoked at indeterminate points. You must use GC.Collect if you want to be sure:
using(C c = new C())
{
c.UseLimitedResource();
GC.Collect();
}
Regards
Thomas
www.thomas-weller.de
Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
Programmer - an organism that turns coffee into software.
modified on Friday, November 21, 2008 5:26 AM
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You are wrong: the purpose of the using keyword is exactly to call the Dispose method at the end of a scope.
The misunderstanding here is that Dispose has to be used to release unmanage resources used by an object, not to release the object itself. So, if you declare an object outside an using scope, the object and its (managed) properties are still accessible.
Try rewriting the OP example using a FileStream instead to a custom class: outside the using scope the stream object is still accessible, but you can no longer use it to read or write data.
All is explained, as usually, in MSDN[^].
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As the other guy pointed out, the GC does not call Dispose(), because it does know about it. What it knows about, is the finalizer, which usually calls the Dispose() method.
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Thomas Weller wrote: You must use GC.Collect if you want to be sure
No, you shouldn't. Calling GC.Collect is a very bad practice. The using statement translates in to a try/finally block where c.Dispose will be called in the finally.
Scott Dorman Microsoft® MVP - Visual C# | MCPD
President - Tampa Bay IASA
[ Blog][ Articles][ Forum Guidelines]
Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai
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There is nothing magical about the Dispose method. If the Dispose method doesn't do anything to make the object unusuable, it's still usable after the Dispose method has been called.
I think that you are confusing disposal with garbage collection. The object can be collected when it's not used any more, and there is no direct connection between disposal and garbage collection.
The IDisposable interface is used when there is a need to control the life cycle of an object. There is no destructors in .NET (as in systems that use reference counters instead of garbage collection), i.e. an object is not removed instantly when you remove the last reference to it. The garbage collector collects the object eventually, but you have no control over when that happens, so that can't be used reliably to clean up unmanaged resources.
(Eventhough memory is a limited resource, it's managed, so the garbage collector can safely free up large memory structures on it's own.)
Despite everything, the person most likely to be fooling you next is yourself.
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As Guffa said, calling Dispose does not actually release the memory used by the object. It simply helps tell the GC that you're done using the object. The GC will determine when it should be "collected" and the memory reclaimed. Until that happens, the object is still accessible.
By the way, you shouldn't explicitly implement Dispose as this doesn't follow the Dispose pattern properly. See this article[^] for more details.
Scott Dorman Microsoft® MVP - Visual C# | MCPD
President - Tampa Bay IASA
[ Blog][ Articles][ Forum Guidelines]
Hey, hey, hey. Don't be mean. We don't have to be mean because, remember, no matter where you go, there you are. - Buckaroo Banzai
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I created an application in vs2003, created report of that application, then created Setup of that application using VS.
Also checks the setup/install after creating it on same machine on which i had developed application. It works fine and reports too.
But when I install the application on different machine application is working but while fetching data in crystal viewer its giving error.
May be some helping files are required to show the report properly  ,
any help or comments !!
thanks and regards.
the error:
See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.
************** Exception Text **************
CrystalDecisions.CrystalReports.Engine.InternalException: Cannot find KeycodeV2.dll, or invalid keycode.
at .F(String , EngineExceptionErrorID
)
at .B(String , Int32 )
at CrystalDecisions.CrystalReports.Engine.ReportDocument.;()
at CrystalDecisions.CrystalReports.Engine.ReportDocument.InternalInit()
at CrystalDecisions.CrystalReports.Engine.ReportDocument..ctor()
at CrystalDecisions.CrystalReports.Engine.ReportClass..ctor()
at WpcDetails.CRWPC..ctor()
at WpcDetails.frmSearch.cmdName_Click(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
************** Loaded Assemblies **************
mscorlib
Assembly Version: 1.0.5000.0
Win32 Version: 1.1.4322.573
CodeBase: file:----------------------------------------
Wpc
Assembly Version: 1.0.3247.19842
Win32 Version: 1.0.3247.19842
CodeBase: file:----------------------------------------
System.Windows.Forms
Assembly Version: 1.0.5000.0
Win32 Version: 1.1.4322.573
CodeBase: file:----------------------------------------
System
Assembly Version: 1.0.5000.0
Win32 Version: 1.1.4322.573
CodeBase: file:----------------------------------------
System.Drawing
Assembly Version: 1.0.5000.0
Win32 Version: 1.1.4322.573
CodeBase: file:----------------------------------------
System.Data
Assembly Version: 1.0.5000.0
Win32 Version: 1.1.4322.573
CodeBase: file:----------------------------------------
System.Xml
Assembly Version: 1.0.5000.0
Win32 Version: 1.1.4322.573
CodeBase: file:----------------------------------------
Accessibility
Assembly Version: 1.0.5000.0
Win32 Version: 1.1.4322.573
CodeBase: file:----------------------------------------
CrystalDecisions.Windows.Forms
Assembly Version: 9.1.5000.0
Win32 Version: 9.1.9800.0
CodeBase: file:----------------------------------------
CrystalDecisions.Shared
Assembly Version: 9.1.5000.0
Win32 Version: 9.1.9800.0
CodeBase: file:----------------------------------------
CrystalDecisions.CrystalReports.Engine
Assembly Version: 9.1.5000.0
Win32 Version: 9.1.9800.0
CodeBase: file:----------------------------------------
CrystalKeyCodeLib
Assembly Version: 9.1.5000.0
Win32 Version: 9.1.9800.0
CodeBase: file:----------------------------------------
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In my application i have a form designed with 8 Usercontrols (pages), 1 StatusStrip (bottom) and 1 ToolStrip (top).
The application works like this: i press a button to switch usercontrols, that work as pages, so, i go from menu login_page to menu_page
and from there to any other page.
I manage all this with the help of a visibility method delegate.
Login_page load is different from all, only because ToolStrip is not visible, in any other "page" load both ToolStrip
and StatusStrip are visible.
(i do that because in login_page i manage logins, so only after login i allow ToolStrip controls to the user!!!, so, before login the toolstrip is not visible)
So whats wrong? nothing. When i open the project in c# (not run it) i get the message bellow inside the form, but
when i run it everthing works sweet, 100% like i want.
<System.NullReferenceException: Object reference not set to an instance o an object.
at
Use_Usercontrols_as_Pages.Usercontrol_PageMenu.Usercontrol_PageMenu_VisibleChanged
(object sender, eventargs e) in ...UserControls_as_pages|use_usercontrols_as_Pages\Usercontrol_PageMenu.cs:line 56
at system.windows.forms.controls.onvisiblechanged(eventargs e)
at system.windows.forms.scrollablecontrol.onvisiblechanged(eventargs e)
at system.windows.forms.control.onparentvisiblechanged(eventargs e)
at system.windows.forms.scrollablecontrol.onvisiblechanged(eventargs e)
at system.windows.forms.form..onvisiblechanged(eventargs e)
at system.windows.forms.control.wmshowwindow(message&m)
at system.windows.forms.scrollablecontrol.wndproc(message&m)
at system.windows.forms.containercontrol.wndproc(message&m)
at system.windows.forms.form.wndproc(message&m)
at system.windows.forms.form.wndproc(message&m)
at system.windows.forms.control.controlnativewndow.onmessage(message&m)>
nelsonpaixao@yahoo.com.br
trying to help & get help
modified on Thursday, November 20, 2008 7:35 PM
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When I was an MVP, I reported this as a bug. MS thinks it's a feature, but in fact, it's one of the stupidest changes they've ever made. The IDE runs some, but not all, of your code, and if your code doesn't work when only part of it is run, it won't show in the designer. If you attach one instance of the IDE to another, then you can use the IDE to 'debug' your code. Of course, your code is not broken, the IDE is. You will need to rework your code if you want to use the designer. Which is the stupidest thing ever.
Christian Graus
Driven to the arms of OSX by Vista.
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hi, thanks for the post. 
this application is meent to be my first article submition to codeproject you know? but i really dont know what to make of this, like i said everthing works!!!
i think is not nice to submit a article with that kind of ..."error" or what ever it is
i really dont know that IDE stuff you know?! where can "find" it to change?
nelsonpaixao@yahoo.com.br
trying to help & get help
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Like I said, attach one IDE to another, then try to view the control in the designer, your attached IDE will catch the 'exception' and show you where an object in your code is in a bad state, because not all of your code was run by the IDE.
Christian Graus
Driven to the arms of OSX by Vista.
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Hi,
as the exception indicates, have a look at line 56 of file Usercontrol_PageMenu.cs
chances are adding a null test will fix things.
BTW: make sure your IDE always shows line numbers, that will make things a lot easier:
Compiler errors and run-time exceptions tend to show line numbers
(look at Exception.ToString(), not Exception.Message).
The Visual Studio editor can show them too, but for some mysterious reason does not
do so by default; see menu Tools/Options/Text Editor/All Languages/General/...
If you turn them on, you'll locate problem spots much more easily.
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crap, i going to figure it out some how 
nelsonpaixao@yahoo.com.br
trying to help & get help
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Can some one give me a link which has good demo on how to use the code generated by SQLMetal
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hi i have a dataset which consists of one tables. i need to filter this data set and store it in another table. how can i do this?
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A dataset allows you to set a filter. Then I'm not sure if there's a quicker way than just to iterate over the records and store them.
Christian Graus
Driven to the arms of OSX by Vista.
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Hi ..
There is a quicker way ... use the Select Method of the DataTable
ds.Tables[0].Select(filterExpression); ... read this MSDN article regarding the Select method ... it will help you ...
http://msdn.microsoft.com/en-us/library/det4aw50.aspx[^]
Hope this helps ...
Sincerely Samer Abu Rabie
Note: Please remember to rate this post to help others whom reading it.
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Use a dataview to do the filtering and you can copy the filtered dataview to a new table (dvData.CopyTable I think)
Never underestimate the power of human stupidity
RAH
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hi evryone
i have big problem using com1
i have 9 pin cable (rs232)
i need to light LED from rs232
i try to wright:
port.Write(new byte[] { 0x1B, 0x4C, 0x30, 0x1B, 0x1A }, 0, 5);
but the LED not light
how can i know what to send to recive signal that light the LED,
and what pin's i need to connect to the LED
thank's alot for any help
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Try network byte order?
Need software developed? Offering C# development all over the United States, ERL GLOBAL, Inc is the only call you will have to make.
Happiness in intelligent people is the rarest thing I know. -- Ernest Hemingway
Most of this sig is for Google, not ego.
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what ??  
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still no answer
any one ??....
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Hi,
you failed to sufficiently explain the problem:
- how is the LED connected to the PC? is it attached to a microcontroller of some kind?
if so, which one, what is the command set of the interface?
if not, I must assume it is connected straight to one of the RS232C control pins, so which one, and why would you need to send data bytes then? 5 bytes sent at an unknown baud rate take a few milliseconds at most, so if the LED is connected to the RS232C TxD pin, it gets energy for that long, and the human eye will not notice it al all.
- you did include a series resistor I hope, otherwise the LED has been killed already.
- how does this relate to C#?
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Can/would somebody tell me how to display an icon on a form in C# please (Windows CE 5.0)? I have to display the battery level of a remote sensor on a form. I created several icons, with VS, and depending on its battery level I will pick the corresponding icon file. I'm new to C# and Windows CE 5.0 and I'm sure it’s easy to do but I'm not having any luck with the searches.
Thanks,
Bob
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