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Hi!
I am quite new to C# and have noticed that one cannot give default values to arguments. Any idea why this is not implementend in C#? 
Best regards,
Alexandru Savescu
P.S. Interested in art? Visit this!
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Alexandru Savescu wrote:
Any idea why this is not implementend in C#?
As I've read, this leads to versioning problems. Where does the default is defined? On the client or in the interface implementation?
It's not the fall that kills you: it's the sudden stop - Down by Law, Jim Jamursch (1986)
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I think I was not clear enough. I meant default argument values to functions like in C++:
void f (int x = 0)
{
printf ("%d", x);
}
Best regards,
Alexandru Savescu
P.S. Interested in art? Visit this!
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Alexandru Savescu wrote:
I think I was not clear enough.
No, you were. I wasn't, sorry.
This page explains it better than me:
"
Because IL always calls a method passing a complete set of arguments, the value of an absent argument is determined at compile time, not at run time. This has versioning consequences. For example, say a ComponentAssembly.dll assembly contains a method that has an optional Int32 argument whose default value is 5. Now imagine an AppAssembly.exe assembly that contains a call to this method and the optional argument isn’t specified. When compiling AppAssembly.exe, the compiler emits IL code that passes 5 to the method. Let’s say that the method in ComponentAssembly.dll has its optional parameter’s default value changed to 123 and the assembly is rebuilt. If the AppAssembly.exe assembly isn’t rebuilt, then at run time, 5 is passed to the method—the new default value (123) isn’t passed to the method unless the code in AppAssembly.exe is also recompiled.
"
http://www.microsoft.com/mspress/books/sampchap/6199e.asp[^]
It's not the fall that kills you: it's the sudden stop - Down by Law, Jim Jamursch (1986)
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Thanks, that clarifies it.
Best regards,
Alexandru Savescu
P.S. Interested in art? Visit this!
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One way to get around this issue would be for the c# compiler to auto-generate the necesary method overloads for optional params.
for instance:
public void Foo(Int32 i = 5){...}
would get compiled to:
public void Foo(Int32 i) {...}
public void Foo() { Foo(5); }
This would allow the value of the optional paramter to be stored in the correct assembly for versioning issues.
It's not a perfect solution, but it works pretty well.
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Andy Smith wrote:
public void Foo(Int32 i) {...}
public void Foo() { Foo(5); }
This would allow the value of the optional paramter to be stored in the correct assembly for versioning issues.
Nice idea. 
-Nick Parker
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Can anyone point out me where i am wrong. The below code creates a user defined parameter object for a Command object in ADO.NET. I am just trying to type cast this parameter object with OracleParameter but i am getting invalid casting error.
Your help in this regard is highly appreciated.
Cheers
Venkat
using System;
using System.Data;
namespace venkat
{
///
/// This class is used to store the parameter information for a
/// command or a stored procedure.
///
public sealed class SPParameter: MarshalByRefObject,IDbDataParameter, IDataParameter, ICloneable
{
#region Private fields
private int m_DataType;
private DbType m_dbType;
private ParameterDirection m_Direction;
private bool m_blnIsNullable;
private string m_strParamName;
private string m_strSourceColumn;
private DataRowVersion m_oDataRowVersion;
private object m_oValue;
private byte m_bytePrecision;
private byte m_byteScale;
private int m_intSize;
#endregion
#region Public Attributes/properties
public int DataType
{
get{
return m_DataType;
}
set
{
m_DataType = value;
}
}
public DbType DbType
{
get{return m_dbType;}
set{m_dbType = value;}
}
public ParameterDirection Direction
{
get{return m_Direction;}
set{m_Direction = value;}
}
public bool IsNullable
{
get{return m_blnIsNullable;}
set{m_blnIsNullable = value;}
}
public string ParameterName
{
get{return m_strParamName;}
set{m_strParamName = value;}
}
public string SourceColumn
{
get{return m_strSourceColumn;}
set{m_strSourceColumn = value;}
}
public DataRowVersion SourceVersion
{
get{return m_oDataRowVersion;}
set{m_oDataRowVersion = value;}
}
public object Value
{
get{return m_oValue;}
set{m_oValue = value;}
}
public int Size
{
get{return m_intSize;}
set{m_intSize = value;}
}
public byte Precision
{
get{return m_bytePrecision;}
set{m_bytePrecision = value;}
}
public byte Scale {
get{return m_byteScale;}
set{m_byteScale= value;}
}
#endregion
#region Public member
public object Clone()
{
return this;
}
#endregion
///
/// Default constructor. Initialize member variables to default value.
///
public SPParameter()
{
this.m_blnIsNullable = false;
this.m_oValue = null;
this.m_strParamName = null;
this.m_strSourceColumn = null;
}
}
}
Cheers,
Venkatraman Kalyanam
Chennai - India
"Being Excellent is not a skill, it is an attitude"
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You can only cast to supertypes iow, base classes and inferfaces. [edit]if you do not define others[edit]
I rated this article 2 by mistake. It deserves more. I wanted to get to the second page... - vjedlicka 3:33 25 Nov '02
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Hello,
Please someone explain to me which is the need of Sychronized and SyncRoot in .NET collections. Why and how should I use this two features. Aren't the collections thread safe?? And if them aren't, a lock is not enough? Really, I think I have a big missunderstood about collections, please help.
Thanks,
Miguel
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I'm not expert here, but here is my understanding.
I believe most of the collections have the SyncRoot element, and when you are locking the collections you need to lock the SyncRoot element.
So if you are locking a hastable, it should look something like
lock(myhashtable.SyncRoot).
The locking keyword in c# is a bit misleading, actually what it does is grant you access to the lock, so that no other thread can acquire the lock until you release it.
regards
Kannan
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Don Miguel wrote:
which is the need of Sychronized
Synchronized tells you if the collection's operations will be thread-safe. Generally this is done by implementing a wrapper around the collection, using a lock on the SyncRoot for each operation performed.
Don Miguel wrote:
which is the need of SyncRoot
SyncRoot is for doing your own locking. Say you need to add a lot of items to the collection, during which no other thread should use it. Rather than using the Synchronized wrapper which would lock/unlock for each operation you would create a lock on the SyncRoot object, then perform each of your operations.
Don Miguel wrote:
Aren't the collections thread safe??
No, you need to refer to the documentation for each class you wish to use to find out if the operations are thread-safe. Making everything thread-safe by default is expense CPU wise, so you are better off not putting it in for the cases where thread-safety isn't an issue.
Most collection classes expose some way of getting a Synchronized version, usually by a static method of some sort. Always check the documentation to be sure.
James
"It is self repeating, of unknown pattern"
Data - Star Trek: The Next Generation
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Many thanks James!
You was very explicit, it helps me much.
Don Migule
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Hello,
How do I share data in my DLL with with other DLLs?
Chito
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I think I have come across a fairly common situation but I cant find any help with this.
I have a simple form with 2 controls. A text box (Employee's Name) and a combo box (Employee's Job Title). I have a DataTable that I have tied both the text box and combo box to. Changing positions using the CurrencyManager works fine and everything is good.
But now I want to populate the combo-box with a list of all available jobs. I want to be able to select a item from the list and have it update the appropriate row in my DataTable as would an edit within the text box.
I have the following code, but I get un-expected results.
<br />
DataTable jobs = new DataTable("Jobs");<br />
jobs.Columns.Add("Job", typeof(string));<br />
jobs.Rows.Add(new object[] {"Software Engineer"});<br />
jobs.Rows.Add(new object[] {"Project Manager"});<br />
jobs.Rows.Add(new object[] {"Tester"});<br />
jobs.Rows.Add(new object[] {"Documenter"});<br />
jobs.Rows.Add(new object[] {"Project Lead"});<br />
<br />
cboJob.DataSource = t;<br />
cboJob.DisplayMember = "Job";<br />
<br />
DataTable namesAndJobs = new DataTable("NamesAndJobs");<br />
namesAndJobs.Columns.Add("Name", typeof(string));<br />
namesAndJobs.Columns.Add("Job", typeof(string));<br />
<br />
namesAndJobs.Rows.Add(new object[] {"Bob", "Project Lead"});<br />
namesAndJobs.Rows.Add(new object[] {"Mark", "Documenter"});<br />
namesAndJobs.Rows.Add(new object[] {"Henry", "Project Manager"});<br />
<br />
txtName.DataBindings.Add("Text", namesAndJobs, "Name");<br />
cboJob.DataBindings.Add("Text", namesAndJobs, "Job");<br />
Can what I want to do, even be done? If not, what is the purpose of allowing multiple DataBindings to the same control?
"I am so smart. S-M-R-T. I mean, S-M-A-R-T" - Homer
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I was wondering how I would center the form when it loads? In VC++ and VB I believe there is a setting to center the form. But I don't see it in the properties. So the other way I was planning on doing this was to do something similar to
Form.Left = (Screen_Width+Form_Width/2)
for the width and height, but for that I need to know how to get the screen width.
Any help on either method or another one will be much appreciated.
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I found it.
// Center the Form on the user's screen everytime it requires a Layout.
this.SetBounds((Screen.GetBounds(this).Width/2) - (this.Width/2),
(Screen.GetBounds(this).Height/2) - (this.Height/2),
this.Width, this.Height, BoundsSpecified.Location);
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I don't know your specific circumstance but this code will always keep the form centered in the screen. This may or may not be desirable, personally I'd find it far too annoying to even use your app anymore.
To center a form on the screen at startup, set the StartupPosition property of the Form to FormStartupPosition.CenterScreen.
Even better is to do the above the first time the app is run, then store user preferences so they don't have to keep resizing/moving the form everytime they run your app.
Of course I don't know your circumstances so you may have a good reason for doing so (kiosk, controller, etc.).
James
"It is self repeating, of unknown pattern"
Data - Star Trek: The Next Generation
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Is there a way to differentiate between an event that is fired from the mouse vs. programmatically...??? For example, I need to be able to differentiate between a mouse clicking a treeview checkbox vs. my code setting a checkbox.
If you set a checkbox in the code with this statement:
"node.Checked = e.Node.Checked;"
it triggers the treeview AfterCheck event, just as if you'd clicked it with the mouse.
I only want the event to be fired from a mouse click... is there a way to do this?
thanks.
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A scenario I've used is with a global variable:
private bool m_ProgClick = false;
public void Foo()
{
...
m_ProgClick = true;
node.Checked = e.Node.Checked;
m_ProgClick = false;
...
}
protected void OnClick(...)
{
if (!m_ProgClick)
{
}
}
I've also used a stack to implement multiple places in the code that need to bypass the Click event (or other similar types of events). Write me if you want the details.
α.γεεκ Fortune passes everywhere.
Duke Leto Atreides
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Try this:
private void treeView1_AfterCheck(object sender, System.Windows.Forms.TreeViewEventArgs e)
{
if (e.Action == TreeViewAction.ByMouse)
{
MessageBox.Show("ByMouse");
}
}
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Try digging into the event arguments that are passed to you.
e.something may identify that a mouse click occured. That way
your coding is based off what is passed to you in the event and
you become independant of internal code.
_____________________________________________
The world is a dangerous place.
Not because of those that do evil,
but because of those who look on and do nothing.
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Please. I need to do a search for the not less or greater key than a specific value and using System.Collections like Hashtable, SortedList, ... in the same way as using STL map upper_bound and lower_bound functions. How could I do?
Thanks.
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Same problem !!!
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