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Hi All,
Does anybody of you know how to get distinct rows from DataView or DataTable.
Thanks
Ruchi
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The best way is to use the DISTINCT keyword in your SQL statement that fills the DataSet (which contains the DataTable) or the DataTable, but if for some reason you can't you could try a couple different ways.
The default implementation does support getting distinct values as a simple method call, but you could either sort the DataView, enumerate it and skip adjacent duplicates; or keep a look-up table of what you've already enumerated and compare that as you enumerate your DataTable. In most cases, the former method would be faster and would consume less space.
If you use a look-up table, consider a Hashtable with the distinct field as the key and a reference to your DataRow as the value (it'll be a reference, not a copy, making retrieval faster...unless you clone).
Microsoft MVP, Visual C#
My Articles
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HI,
Similar to what you suggested, I got an article on Microsoft website. It works but the limitation is what if DISTINCT is to be applied on multiple columns
http://support.microsoft.com/default.aspx?scid=kb;en-us;326176
Add the following Private method to the class definition. This method is the same as the method that is used in other DataSetHelper articles. It is used to compare field values (including NULL).
private bool ColumnEqual(object A, object B)<br />
{<br />
<br />
<br />
if ( A == DBNull.Value && B == DBNull.Value )
return true; <br />
if ( A == DBNull.Value || B == DBNull.Value )
return false; <br />
return ( A.Equals(B) );
}
Add the following Public method to the class definition. This method copies unique values of the field that you select into a new DataTable. If the field contains NULL values, a record in the destination table will also contain NULL values.
public DataTable SelectDistinct(string TableName, DataTable SourceTable, string FieldName)<br />
{ <br />
DataTable dt = new DataTable(TableName);<br />
dt.Columns.Add(FieldName, SourceTable.Columns[FieldName].DataType);<br />
<br />
object LastValue = null; <br />
foreach (DataRow dr in SourceTable.Select("", FieldName))<br />
{<br />
if ( LastValue == null || !(ColumnEqual(LastValue, dr[FieldName])) ) <br />
{<br />
LastValue = dr[FieldName]; <br />
dt.Rows.Add(new object[]{LastValue});<br />
}<br />
}<br />
if (ds != null) <br />
ds.Tables.Add(dt);<br />
return dt;<br />
}
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Yes, all they're doing here is implementing a custom IComparer with which to sort (not really necessary in most cases since two columns with DBNull.Value would still have the same value, but whatever).
The only good way to do this is to use the DISTINCT keyword in your SQL statement. What's wrong with that?
It's either that, or use look-up tables which could be very expensive, especially with large data sets.
Microsoft MVP, Visual C#
My Articles
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the following are my classes
Class Students.cs
<br />
using System;<br />
using System.Collections;<br />
using System.IO;<br />
using System.Runtime.Serialization;<br />
using System.Xml.Serialization;<br />
namespace WindowsApplication1<br />
{<br />
[Serializable]<br />
public class Students<br />
{<br />
int index = 1;<br />
ArrayList students = new ArrayList();<br />
public Students()<br />
{<br />
}<br />
<br />
<br />
public void AddStudent( string name, string add)<br />
{<br />
Student t = new Student(index++, name, add);<br />
students.Add(t);<br />
}<br />
public void RemoveStudent(int sID)<br />
{<br />
foreach(Student s in students)<br />
{<br />
if (s.StudentID == sID)<br />
{<br />
students.Remove(s);<br />
return;<br />
}<br />
}<br />
return;<br />
}<br />
<br />
public ArrayList Items<br />
{ get {return students;} }<br />
<br />
public Student this[int index]<br />
{<br />
get<br />
{<br />
foreach(Student s in students)<br />
{<br />
if(s.StudentID == index)<br />
return s;<br />
}<br />
return null; <br />
}<br />
}<br />
}<br />
}<br />
<br />
<br />
Class Student.cs
using System;<br />
using System.IO;<br />
using System.Runtime.Serialization;<br />
using System.Xml.Serialization;<br />
namespace WindowsApplication1<br />
{<br />
[Serializable]<br />
public class Student<br />
{<br />
private int intStudentID = 0;<br />
private string strName = "";<br />
private string strAddress = "";<br />
<br />
public Student(){}<br />
public Student(int sID, string n, string a)<br />
{<br />
StudentID = sID;<br />
Name = n;<br />
Address = a;<br />
}<br />
public int StudentID<br />
{<br />
get{return intStudentID;}<br />
set{intStudentID = value;}<br />
}<br />
public string Name<br />
{<br />
get{return strName;}<br />
set{strName = value;}<br />
}<br />
public string Address<br />
{<br />
get{return strAddress;}<br />
set{strAddress = value;}<br />
}<br />
}<br />
}<br />
The following is the code that I have used to attempt to serialize the class.
StreamWriter w = null;<br />
try<br />
{<br />
XmlSerializer ser = new XmlSerializer(typeof(Students));<br />
w = new StreamWriter("class.xml");<br />
ser.Serialize(w, Hstudents);<br />
}
catch (Exception ex)<br />
{<br />
string strErr = String.Format("Unable to serialize class, error '{0}'",<br />
ex.Message);<br />
MessageBox.Show(strErr,"Serialize Error",MessageBoxButtons.OK,<br />
MessageBoxIcon.Error);<br />
}
finally<br />
{<br />
if (w != null) w.Close();<br />
w = null;<br />
}
If i change it to work with binary serialization, the serialization works fine. Is there somethign special that i have to do to the classes to get it to serialize correctly?
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First of all, using a binary formatter implies you're using runtime serialization. Runtime serialization and XML serialization are COMPLETELY different monsters. Don't confuse the two. You can read more about the differences by reading Serializing Objects[^] in the .NET Framework SDK. Also, binary and SOAP serialization are in the System.Runtime.Serialization (and child) namespaces, while XML Serialization is in System.Xml.Serialization.
To answer your question, though, take a look at the XmlArrayAttribute and the XmlArrayItemAttribute that you'd use both on your ArrayList property.
Microsoft MVP, Visual C#
My Articles
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Hey all, I've been working on a wrapper for the WindowsXP Peer-to-Peer sdk for a while now in my free time and I've just completed an initial release of it with enough functionality to create and maintain networks between peers. I'm working on a .Net wrapper because the API is basically written in C and looks clunky in .Net applications. Anways, I'd like to write an article about it for Code Project, but would like some input from people and find out if anyone is having any problems with it. If you know what the WinXP P2P SDK is, then that's great and you should have no problem using this wrapper, otherwise you may have some issues, but hopefully my explanation of how to use it is good enough. Here's the link to the WinP2P.Net (what I've called it so far):
WinP2P.Net[^]
Here's a link to MS's info on what they've done with the API:
Windows XP P2P SDK From Microsoft[^]
Anyways, I hope you all can use this and it works well for you, if not, send me an email or post a message on the forums on the WinP2P.Net site, I check those quite often. Thanks in advance and good coding!! Oh yeah, I've never attempted anything really of this scale, so bear with the bugs that may be in there, I'll do what I can to get them fixed as soon as possible 
Jason Schneekloth
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Sounds like it would be an interesting article. I'll give this a try later.
One thing I might mention - especially being a CodeProject editor - is that it is ".NET", not ".Net". This is a common mistake but is not proper. ".net" is also not allowed in images (i.e., logos) as it is reserved for Microsoft use only. Technically, you're not even supposed to use ".NET" in your product naming, but you're not a commercial solution so it's not like they can do much (although look at "MikeRoweSoft"). Just a heads-up.
Microsoft MVP, Visual C#
My Articles
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Ack! I didn't know that. Hehe, looks like there's gonna be a change in what it's called. Thanks for the head's up
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Ya but all he did was hand over the domain and he got loads of free stuff !
Matthew Hazlett
Windows 2000/2003 MCSE
Never got an MCSD, go figure...
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Heath Stewart wrote:
is that it is ".NET", not ".Net". This is a common mistake but is not proper. ".net" is also not allowed in images (i.e., logos) as it is reserved for Microsoft use only.
.net is an internet root domain, and no-one can tell me how to spell it. 
top secret
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If, for some reason, you were having issues with getting the Advanced Networking Pack installed and started, there are updated instructions in the manual and also in the forums under tech support for WinP2P.
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Thanks to this great site and the great people contributing source code examples, I've managed to create my first C# application! woot woot woot!
The only problem I'm having is that my application launches internet explorer for every url that I click on (from a list of urls). Instead of having a new instance of internet explorer started everytime, is there a way to find an existing instance of iexplorer and change it's url?
Currently, I can find an existing instance of iexplorer bring it to the foreground via "SetForegroundWindow" in user32.dll, but I don't know how to change it's url?
Can anyone help me on this?
Thanks.
Chris.
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One way is to simply use ShellExecute. The default implementation in windows is to use a running instance of Internet Explorer (or whatever the default browser is, which is often the preferred way anyway):
ProcessStartInfo info = new ProcessStartInfo(url);
info.UseShellExecute = true;
Process.Start(info); You can also use the InternetExplorer out-of-process server if you want to force the user to use IE. This represents the fore-most instance of IE. First create an interop assembly of Internet Explorer by either typing the following:
tlbimp.exe /out:Interop.SHDocVw.dll %WINDIR%\system32\shdocvw.dll Or using VS.NET to add a COM reference to the "Microsoft Internet Controls" (shdocvw.dll). Then create an instance of the InternetExplorerClass like so:
InternetExplorerClass ie = new InternetExplorerClass();
object url = url;
object missing = Missing.Value;
ie.Navigate2(ref url, ref missing, ref missing, ref missing, ref missing); See Programming and Reusing the Browser[^] for more details.
If you want to host the WebBrowser control (the control that is actually IE, which also hosts MSHTML, the Microsoft HTML rendering engine), you can additionally run:
aximp.exe /out:AxInterop.SHDocVw.dll %WINDIR%\system32\shdocvw.dll to create an ActiveX host for the WebBrowser control (by default, named AxWebBrowser), which you can host in your forms and container controls. You can find more information about this in the link above (related to the COM interfaces exposed by WebBrowser and MSHTML). There's also several articles here on CodeProject that described advanced hosting using .NET. Just search (a good query term is "IDocHostUIHandler").
Microsoft MVP, Visual C#
My Articles
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Hi Heath,
thanks for the quick response!
I tried the first option of using UseShellExecute but that didn't work for me. Reason was because in the IE options, the option of "Reuse Windows for Launching Shortcuts" was unchecked. When I had this checked, it worked.
Thanks.
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Actually, you should honor the user's preferences as much as possible. Last time I checked, that option should be turned on anyway (it also affects browsing with Windows Explorer).
As I said, though, if you want to force users to use IE with your app (and there's good reasons, though they are usually more suited to hosting the WebBrowser control) you can use the second method I mentioned - the out-of-process automation server for IE.
Microsoft MVP, Visual C#
My Articles
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I have made a control whice inherits from Listbox, and made it ownerdraw...
In the OnDrawItem i have the following code:
base.OnDrawItem(e);
e.DrawBackground();
Graphics g = e.Graphics;
Bitmap b = new Bitmap(30, 30);
Graphics gs = Graphics.FromImage(b);
Brush brush = Brushes.Red;
gs.FillRectangle(brush, 0f, 0f, 30f, 30f);
g.DrawImage(b, e.Bounds.Left + 5, e.Bounds.Top + 5);
Brush myBrush = Brushes.Black;
g.DrawString("hey", e.Font, myBrush,e.Bounds, StringFormat.GenericDefault);
The text is drawed fine, but the bitmaps only blinks and then they are gone. If I scroll the listbox everything is showed fine, but if I minimize and maximize the application (force a redraw) the bitmaps are now drawn.
If I select an item, the bitmap for that item is showed just fine 
Any ideas?
- Anders
Money talks, but all mine ever says is "Goodbye!"
ShotKeeper, my Photo Album / Organizer Application[^]My Photos[^]
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Not sure if this would cause that particular problem, but be sure to dispose your Graphics object that you use to fill the Bitmap. The using statement is handy for this since it would be disposed even if any exceptions occur.
Microsoft MVP, Visual C#
My Articles
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I didn't figure it was, but thought I'd mention it anyway.
When you click on an item after the images fail to display, and then click on another item, does the bitmap continue to display fine? What if you scroll the list again - do the items that were out of view and are not in view display the bitmaps correctly?
Microsoft MVP, Visual C#
My Articles
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When I click an item and then click another item both images shows just fine, and when scrolling everything works as expected...
But when minimize/maximize the bitmaps goes away again...
Really strange...
- Anders
Money talks, but all mine ever says is "Goodbye!"
ShotKeeper, my Photo Album / Organizer Application[^]My Photos[^]
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Definitely a refresh bug, then. Try setting ControlStyles.AllPaintingInWmPaint and ControlStyles.UserPaint to true using SetStyle in your constructor.
Microsoft MVP, Visual C#
My Articles
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All those list-type views are always funky when it comes to painting.
It's a bit of a hack, but how about calling Refresh (invalidates and forces an immediate update) in an override to Visible (when set to true) or something along those lines.
Sorry for all the responses. I've just never seen this behavior before, and I've seen (and usually fix) a lot of painting bugs (the ubiquitous ListView being the usual suspect).
Microsoft MVP, Visual C#
My Articles
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I just tried to make a simple listbox in my application, and making it ownerdraw, and added the code from my first post to the drawitem eventhandler...
Same problem when I minimize/maximize the app....
So when the control is refreshed, it erases everything, kinda strange...
And yeah, I have never seen this one before, and I have done lots of ownerdrawing in my time. (i actually prefer drawing in C++  )
- Anders
Money talks, but all mine ever says is "Goodbye!"
ShotKeeper, my Photo Album / Organizer Application[^]My Photos[^]
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