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Are classes always passed by reference to a method? I am getting the same results with and with out the ref keyword with a class. But when i use a int I get ref/value using them in the respective way. Is there anyway to pass a class by value?
thanks
-hammackj
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There's reference types and value types in .NET. Structs, enums, numeric types, booleans and chars are all value types. Everything else is a reference type. Like their names, reference types are always passed by ref while value types are passed by value, though you can - as you've found - use the ref and out (no initialization required) keywords to pass them by ref.
When you get into P/Invocation, keep this in mind. A pointer to an interface or class should not use the ref or out keywords, while a pointer to a struct or a numeric parameter should.
Microsoft MVP, Visual C#
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Thanks a ton sir. Clears up everything.
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Actually classes are also passed by value. You're passing a value of a reference.
If you call methodA(A a) and in the methodA you say: a = new A(...), the value of the a will not be changed in the caller scope. But if your method signature is: methodA(ref A a) and then in method you say a = new A(...) then in your caller scope value of a will change.
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Variables are passed by value. The class is still passed a reference. Performing any operation on that instance still occurs on the same instance, while it wouldn't on a value type. You're right about the variable, however. There is a difference, though.
Microsoft MVP, Visual C#
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Hallo, I have a strange problem:
When I use DrawString in a drawitem event the text ignores font and brush.
I have a listbox, the unselected items catch the font and brush, but the selected item doesn't. It is printed as unselected.
Do you have any answer??
Bye
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The DrawItemEventArgs contains the properties you need to draw the items, but you must use its State property to determine the state of items, like whether or not it is selected. Keep in mind that since the DrawItemEventArgs.State property uses a flag enumeration, you must use bitwise operators to determine state. For instance, to find out if the item is selected, use something like the following:
bool selected = (e.State & DrawItemState.Selected) != 0;
if (selected)
{
}
else
{
}See Resizable ListBox[^] for a pretty good example (there's many others, too - I just still had that URL in my clipboard used for another reply just a minute ago).
Microsoft MVP, Visual C#
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I am trying to do a word wrapping in the items of the ListBox.
But I donot see any such property provided by ListBox.
Any idea how can I do this.
Any help would be appreciated.
Thanks,
Binal
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You have to owner-draw the items, and there are a couple articles here on CodeProject that explain how. See An editable multi-line listbox for .NET[^] or Resizable ListBox[^] for a couple decent examples.
Basically, you just owner-draw the ListBox using a multi-line StringFormat and call Graphics.DrawString with that StringFormat. Slightly more is involved, but see the articles for details.
Microsoft MVP, Visual C#
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i try to much to deal with the video in the C#
i try to use DShowNet but i don't understand its functions so i need so urgent to know
1- the class or library or dll ..... used to deal with a video in the program
2- i need to cut the video into frames and give each frame its index
3- convert the frames into images
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If you're the same person that posted something similar a couple days ago, I gave you a link to one article here on CodeProject. If you don't understand it's functions, read any documentation available including source code comments or ask the authoring using the message board at the bottom.
No one's just going to give you code, and even in such a case you'll still need to understand it in order to implement it. If you're simply looking for a program that can do this, there are hundreds out there, even some installed with your OS (Microsoft Movie Maker, for example, can slice WMVs).
Microsoft MVP, Visual C#
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Hi Guys,
Im trying to display the ID (Next New One) on the form each time the New Record is entered. I m using this code, but it displaying the wrong ID.
this.txtFileId.Text = ((int)myDs4.Tables["tblFiles"].Rows[myDs4.Tables["tblFiles"].Rows.Count - 1]["fid"] + 1).ToString();
where 'fid' is the column in Table with autonumber type.
Thanx in advance.
Regards
msls
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A new record which hasn't been committed with data yet won't have a new ID. The data must be committed to a row before the ID exists in the DataRow. This is why record navigators (including the DataGrid itself) display a "*" until the record is committed.
Microsoft MVP, Visual C#
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Thanx for ur reply. If u look in my code, I m trying to get Id of last record and trying to add 1 into that but it still not giving me the correct id of the last record. coul du pls confirm the code to access last record in OK or something wrong into that.
Thanx
msls
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This would only work if your DataTable was sorted by ID.
Microsoft MVP, Visual C#
My Articles
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Thanx alot, its working now. I was thinking that coz the ID field id automuner and PK as well in the table, it would be sorted by default.
Thanx
msls
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Hi
Someone knows, if it's possible regenerate a print preview? I have a form with a Print Preview Control, and if I change the paper orientation via a Page Setup Dialog this don't update the print preview. 
Thanks
----
hxxbin
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Is the PrintPage event handler called again? Put a breakpoint in your code and see. Otherwise, handle the StartPageChanged event on the PrintPreviewControl.
Microsoft MVP, Visual C#
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I got a stupid idea:
<br />
this.printPreviewControl1.Document = null;<br />
this.pageSetupDialog1.ShowDialog();<br />
this.printPreviewControl1.Document = this.reportDocument1;<br />
and works  .
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Hi, I want to build MDI Application. I got success in 1st level of MDIChild forms now the problem is that if the 1st level of MDI child form open new forms those forms cannot be included as MDI child becoz those are child forms of the 1st level MDI child form. So could u plz tell me how to proceed in this, to build an application in which all forms as child forms of the main MDI form. or is there any other wayout. Thanks for ur support.
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Whenever you create a new MDI child form, just set the MdiParent property to the main form. So, if a child MDI form created a new child, it's MdiParent is what you'd set as the new form's MdiParent.
See the Form.MdiParent property documentation in the .NET Framework SDK for more information.
Microsoft MVP, Visual C#
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Thank you, i got it running!
frmDlabMenu cpForm = new frmDlabMenu();
cpForm.MdiParent=this.MdiParent;
cpForm.Show();
this.Hide();
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Hi!
In my app I'd like to execute some code when an AppDomain is unloaded. I expected AppDomain.DomainUnload to be suitable for this, however the event never gets raised automatically - only if I call AppDomain.Unload with that AppDomain.
Example:
class Class1
{
static void Main(string[] args)
{
AppDomain.CurrentDomain.DomainUnload += new EventHandler(CurrentDomain_DomainUnload);
AppDomain domain = AppDomain.CreateDomain("Test");
domain.DomainUnload += new EventHandler(CurrentDomain_DomainUnload);
}
public static void CurrentDomain_DomainUnload(object sender, EventArgs e)
{
Console.WriteLine("Unloading appdomain");
AppDomain domain = sender as AppDomain;
if(domain != null)
Console.WriteLine("... unloading domain is: " + domain.FriendlyName);
}
}
I find this quite irritating. How can I implement some kind of per-AppDomain shutdown function?
Thanks in advance. Regards,
Andre Loker
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What about the ProcessExited event?
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ProcessExited only works for the main AppDomain (and even then, I find strange bevahvior to occur).
Regards,
Andre
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