Visual Basic

28-Aug-08 18:01

dBrong wrote:
Are there any system calls I can make to help me find out what's really happening with memory usage?

There aren't any system calls you can make that I am aware of. There may be some unmanged Win32 API calls, but I'm not sure. The best option to see what is happening with the GC is to use some of the performance counters that are built in. Check this post[^] on Channel 9 for more information.

dBrong wrote:
Secondly, is there a list of .net objects that explicity need dispose() to be called manually?

Unfortunately, there really isn't. The best option is to look at the following things:

Does the object provide a Close or Dispose method?
Does the object inherit from IDisposable?

You can also look at the MSDN documentation or use Reflector to check as well. The best rule of thumb is that if the object "feels" like it should be disposed of after you're done using it, it probably implements IDisposable.

dBrong wrote:
I'll wrap the close/dispose in try/catch. I was under the impression that if it failed I'd get a runtime error?

It all depends on how your objects (or the objects you are using) are implemented. If for some reason a disposable object were to throw an exception that was caught and eaten your calling code may not know about it and/or the call to Dispose may never occur. By putting the call to Dispose inside of a finally or using block you can guarantee that it will get called under all conditions.

Scott Dorman

Microsoft® MVP - Visual C# | MCPD
President - Tampa Bay IASA

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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

Re: Possible memory leak

Guffa28-Aug-08 21:51

Guffa

28-Aug-08 21:51

dBrong wrote:
is there a list of .net objects that explicity need dispose() to be called manually?

No, absolutely not. Such a list could never be complete, as the framework is growing with each new version, and there are thousands of thrird party libraries that contain objects that needs disposing.

If in doubt, check if the object has a Dispose method. If it does, there is a reason for that. Not every class that implements IDisposable needs disposing, but unless you have determined that it's actually not needed, you should always call the Dispose method if there is one.

Calling the Dispose method will not hurt even if it is not neccessary for that specific object. For example, you can close a SqlConnection object either by calling the Close method or the Dispose method, as the Dispose method makes sure that the Close method has been called. You can also call the Close method first, then the Dispose method, without harm. You can even call the Dispose method more than once on the same object without problems, you will never get an "object already disposed" error if you happen to call Dispose again.

Despite everything, the person most likely to be fooling you next is yourself.

Classes

CodingYoshi28-Aug-08 11:25

CodingYoshi

28-Aug-08 11:25

Public Class Employee
Public Name As String = Nothing
Public Age As Integer = 0
End Class

Module Module1

Sub Main()
Dim emp1 As New Employee()
emp1.Name = "Calvin"
emp1.Age = 30
Console.WriteLine("Emp1: " & emp1.Name & ", " & emp1.Age)
Dim emp2 As New Employee()
emp2 = emp1
emp2.Name = "Bob"
emp2.Age = 40
Console.WriteLine("Emp1: " & emp1.Name & ", " & emp1.Age)
Console.WriteLine("Emp2: " & emp2.Name & ", " & emp2.Age)
Dim emp3 As Employee = emp1
emp3.Name = "Bryan"
emp3.Age = 50
Console.WriteLine("Emp1: " & emp1.Name & ", " & emp1.Age)
Console.WriteLine("Emp2: " & emp2.Name & ", " & emp2.Age)
Console.WriteLine("Emp3: " & emp3.Name & ", " & emp3.Age)
Console.Read()
End Sub

End Module

Here are the results when run:

Emp1: Calvin, 30
Emp1: Bob, 40
Emp2: Bob, 40
Emp1: Bryan, 50
Emp2: Bryna, 50
Emp3: Bryan, 50

My question is:
How can I copy Emp1 to Emp2 and then if I change the Emp2 only Emp2 is changed, Not Emp1.

Gideon Engelberth28-Aug-08 13:13

Gideon Engelberth

28-Aug-08 13:13

You can create a Copy function on the Employee class that returns a shallow copy of the object.

Public Function Copy() As Employee
    Return CType(Me.MemberwiseClone, Employee)
End Function

then say

Dim emp2 As Employee = emp1.Copy()

I noticed that your example doesn't really gain from having a copy of the object. I'm assuming you have some other case where you don't just override the copied data with new values, because if you just override the old values right away

Scott Dorman28-Aug-08 13:35

28-Aug-08 13:35

The more correct method name would be Clone and potentially implementing the ICloneable interface.

Scott Dorman

Microsoft® MVP - Visual C# | MCPD
President - Tampa Bay IASA

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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

Gideon Engelberth28-Aug-08 17:05

Gideon Engelberth

28-Aug-08 17:05

I did not recommend that interface because it is actually recommended against by Microsoft[^]. The general reason the interface is not recommended is that you do not know if it is a deep or shallow copy (which in this case does not matter), and there are no library functions that really use that interface anyway.

You are right though in suggesting the function name Clone, as it does seem to be more "standard."

Scott Dorman28-Aug-08 17:51

28-Aug-08 17:51

Gideon Engelberth wrote:
I did not recommend that interface because it is actually recommended against by Microsoft

You are absolutely correct. I had completely forgotten about this piece of guidance.

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

Re: Classes [modified]

Scott Dorman28-Aug-08 13:36

28-Aug-08 13:36

The solution Gideon provided is the best one, although the method should be named Clone not Copy ~~and you should possibly implement the ICloneable interface as well~~.

[modification: 28-Aug-2008]The ICloneable interface is actually not recommended[^] per the Framework Design Guidelines.[/modification]

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

modified on Thursday, August 28, 2008 11:51 PM

CodingYoshi29-Aug-08 3:17

CodingYoshi

29-Aug-08 3:17

Thanks guys!

Gideon, yes I will be using it differently. I just used this example to test what happens. However, I still do not understand what is the difference between the following:

Dim emp1 As New Employee()

Dim emp2 as Employee = emp1 ' What is the difference between this
Dim emp2 as New Employee = emp1 ' and this

Automatic printing with VB.Net.

Guffa29-Aug-08 4:28

Guffa

29-Aug-08 4:28

CodingYoshi wrote:
Dim emp1 As New Employee()

That will declare the reference variable emp1, then it will create a new instance of the Emplyee class and assign it's reference to the variable.

CodingYoshi wrote:
Dim emp2 as Employee = emp1

That will declare the reference variable emp2 and assign to it the reference from the varaible emp1. The result is two reference variables that are referencing the same object.

CodingYoshi wrote:
Dim emp2 as New Employee = emp1

That doesn't compile at all, does it? You probably mean:

Dim emp2 as New Employee()<br />
emp2 = emp1

That will declare the reference variable emp2, create a new instance of the Employee class and assign it to the variable. Then it will throw away that instance and instead copy the reference from the emp1 variable. The result is two reference variables that are referencing the same object.

Despite everything, the person most likely to be fooling you next is yourself.

John Kh28-Aug-08 7:46

John Kh

28-Aug-08 7:46

Suppose I have an application that takes orders and save them in an Access databse. And after taking each order I need to print a summary of that order. The summary should contain the items, prices, order number... I need to automatically print this summary right after I save the order. Can this be done in VB.net?

I tried to save the orders in a table called Order1 & the summary in a table called Summary. And I retrieved the need information from Summary to a new form. But this form is being only printed at run time, which I want to avoid?

So is there any way to automatically print the summary for each order, right after the order itself?

I am using a VB.Net application with an Access database.

Thank you in advance.

John,

paas28-Aug-08 8:53

paas

28-Aug-08 8:53

It is not clear to me what you mean by wanting to avoid printing at run time but...

If you want to print via .NET you will need to work with the PrintDocument class (System.Drawing.Printing namespace). I am certain you can find some articles on this site and/or via an internet google that provide examples of working with the PrintDocument class.

Good luck with your project.

John Kh28-Aug-08 9:37

John Kh

28-Aug-08 9:37

The only function I found & worked with me was a function that prints a form at run time. Which means to print the desired form I should open the form, and with a button click on that form the pritings is intiated. Otherwise, The print function will print me the background & not te summary of th order I want.

You get my point now? It is kinda complicated actually. I just can't find the correct printing function.

John,

Low tech Automatic printing

paas29-Aug-08 1:25

paas

29-Aug-08 1:25

You can definitely do what you want to do via the PrintDocument class/object when the order is received, as opposed to just using some function that automatically prints a form with a button click sometime after the order. With the PrintDocument class you would programitically do the formatting (output lines, fonts, etc.) and tell the object what printer to use. It is a little complicated but, once again, there are article examples floating around on this site and elsewhere on the web.

David Mujica28-Aug-08 8:57

David Mujica

28-Aug-08 8:57

Here's a thought ...

1) Create your report with MS-Acess
2) Create a macro in MS-Access that Opens the report and uses the default view of Print, then quits Access; call it myMacro
3) From the command line you could use this syntax to have the report automatically generated: "msaccess c:\temp\db1.mdb /x myMacro"

The idea is that from your VB.net program, you issue the above command line and have MS-Access do the report for you.