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A few months ago some of you helped this hardware engineer with a c background understand that list elements are passed by reference. I solved my immediate problem but have run into another wall.
I have two global lists defined in my form:
List <CUserMem> MemoryBank = new List<CUserMem>(100);
List <CUserMem> CombinedMemories = new List<CUserMem>(100);
After a while, the first list becomes has out of date info and I must "garbage collect" by copying the still-needed elements of the first list to the second list. I simply do :
CombinedMemories[Index].whateverelement = MemoryBank[AnotherIndex].whateverelement;
It works the first time through but of course the next time I update MemoryBank, CombinedMemories is also updated. I tried to avoid this by:
local (temporary) variable = MemoryBank[AnotherIndex].whateverelement;
CombinedMemories[Index].whateverelement = local (temporary) variable;
That doesn't work. After the local variable is destroyed, the two list elements still have the same reference.
So what is the correct way to work with 2 global lists like this?? Can I create a copy of the first list that is not "linked" (have the same reference)???
Thanks -
Chuck
Chuck
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1. Please tell us more about CUserMem and whateverelement so we can help you better.
2. Is it the intention to have each item in one of the lists, but never in both of them?
Luc Pattyn
I only read code that is properly indented, and rendered in a non-proportional font; hint: use PRE tags in forum messages
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CombinedMemories[Index].whateverelement = (cast as appropriate) MemoryBank[AnotherIndex].whateverelement.MemberwiseClone();
This will give you two separate objects with the same contents instead of multiple references to the same object.
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Gerry:
Thanks fot taking the time to reply.
I had seen a couple of references to the fact that cloning a List just copies the references, so you end up with the same problem I started with. See: http://social.msdn.microsoft.com/Forums/en-US/netfxbcl/thread/de75a3c3-2920-48ae-bf85-0399e5ee7a10 and also http://weblogs.asp.net/jeff/archive/2005/11/21/431125.aspx .
But wanting to give it a try anyhow, I took your advice and used MemberwiseClone with your syntax:
CombinedMemories[NumberOfCombinedMemories].bUsed = (Boolean) MemoryBank[i].bUsed.MemberwiseClone();
but get the following error:
Error 3 Cannot access protected member 'object.MemberwiseClone()' via a qualifier of type 'uint'; the qualifier must be of type 'WindowsFormsApplication1.Form1' (or derived from it)
This I do not understand.
Chuck
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Chuck,
I had to make a few assumptions from your original post, assuming you wanted to "clone" a "member" in the list, and not the list itself.
Anyway, cloning a "list" would clone "references" for a "shallow" clone; but would create new objects for a "deep" clone. Same with cloning a single object; shallow cloning would create references for "fields" in the oject that referenced other objects, but would create new objects referenced for by those fields for a deep clone.
Anyway, here is an example of how I understood your problem in the first place; cloning an "element" (ie. object) from one list to another where that element / object does not reference other objects:
(Note that strings, while being reference types, are "deep" cloned in this case ... )
<pre>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace ConsoleApplication1 {
class Program {
static List<Widget> List1 = new List<Widget>();
static List<Widget> List2 = new List<Widget>();
static void Main( string[] args ) {
List1.Add( new Widget() {
Description = "I am a Widget",
OtherData = "12345"
} );
List2.Add( List1[ 0 ] );
Display( "@1" );
List1[ 0 ].Description = "I was changed";
List2[ 0 ].OtherData = "abcde";
Display( "@2" );
List2[ 0 ] = List1[ 0 ].MemberwiseClone();
List1[ 0 ].Description = "I was cloned";
List2[ 0 ].Description = "I am the clone";
Display( "@3" );
}
public static void Display( string location ) {
Console.WriteLine( location + " List1 = {0}; List2 = {1}",
List1[ 0 ].ToString(), List2[ 0 ].ToString() );
}
}
class Widget {
public string Description;
public string OtherData;
public new Widget MemberwiseClone() {
return ( Widget ) base.MemberwiseClone();
}
public override string ToString() {
return Description + "(" + OtherData + ")";
}
}
}
</pre>
modified on Wednesday, November 11, 2009 5:46 PM
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Gerry:
This was a wonderful piece of help with a concrete example to giuide me. I've got the code fixed and I learned something in the process. Can;t beat that combination.
Chuck
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Thanks for the feedback, Chuck. I appreciate it.
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I'm using a stored procedure (proc) for the SqlDataSource1 of my local report (rdlc). I've changed my proc to include an additional field. When I try to edit my local report to add the new field, it does not show up in the dataset or fields under the expression buider. How do I get the dataset to recognize my new field.
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Yes.. this is really a problem with rdlc console.
I think you need to clear the existing dataset from the report to continue.
Right click on rdlc report -> Open With Xml Editor
After you open find <Dataset> and remove its content. Now open the report, add any field to the report, your dataset will be added again with all the fields. (You can also update the report xml with your new field)
Note: Before you do, backup your existing dataset to avoid corrupt of the report.
![Rose | [Rose]](https://codeproject.global.ssl.fastly.net/script/Forums/Images/rose.gif)
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I edited the xml, which solved the problem. Your the best. Thank You very much. 
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Thank you so much...
Cheers.
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Hi there sorry to be a pain again, but is there any simple way of tracking the progress of a object deserialisation??
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What do you mean ? Serialisation takes place in one step, AFAIK.
Christian Graus
Driven to the arms of OSX by Vista.
Read my blog to find out how I've worked around bugs in Microsoft tools and frameworks.
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yes i know serialisation takes place in one step what i need to know is how much of a file it has deserialised as i need to display the percentage to the user while it is deserialising the file (on a background thread)
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Are you deserializing a huge file ??? Actually we deserialise objects which are smaller in size and it takes just a moment to deserilize. I dont know if there is any option as you are not reading the file in bytes. if you read it so, it would also take such a negligible time so that no progress is displayed over screen..
Why do you require such thing. Rather if you are deserializing a collection of objects, you can deserialize each of them, one by one and do generate one event to send percentagecomplete value. 
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private void btn_Next_Click(object sender, EventArgs e)
{
Plugin p = new Plugin();
nextImage = nextImage++;
string _Ext = p.Ext;
ass = Assembly.GetExecutingAssembly();
imageStream = ass.GetManifestResourceStream("NameSpace.Images." + nextImage + _Ext);
pictureBox1.Image = new Bitmap(imageStream);
this.btn_Previous.Enabled = true;
if (nextImage == p.End + 1)
{
this.btn_Next.Enabled = false;
}
}
I'm wondering how to write this to make it work, and make it clean, any suggestions?
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DarkKitten wrote: nextImage = nextImage++;
Weird. You should buy a beginners C# book and read it.
DarkKitten wrote: I'm wondering how to write this to make it work, and make it clean, any suggestions?
When I've done this, I've wrapped the calls to getting resources from the application in a method so I pass in the name and get out the image. Beyond that, you could use useful variable names. What on earth is Plugin, and why do you create one every time ?
Christian Graus
Driven to the arms of OSX by Vista.
Read my blog to find out how I've worked around bugs in Microsoft tools and frameworks.
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Christian Graus wrote: DarkKitten wrote:
nextImage = nextImage++;
Weird. You should buy a beginners C# book and read it.
hehehe, I can usualy write C# code.. I wrote a game emulator with C#..
This is my first attempt at writeing an image viewer and bam i'm having issues weird..
and plugin is the Class.cs that contains information, like the public int for what the Start Image number is, the Extention of the image, ect..
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DarkKitten wrote: hehehe, I can usualy write C# code.. I wrote a game emulator with C#..
Then you wouldn't do nextImage = nextImage++;, you would just have nextImage++;
Furthermore, you stated (unless I misunderstood) that the Plugin instance you create each time the method is called contains the count for nextImage.
Fair, but then wouldn't you have
plugin p = new plugin();
p.nextImage++;
this.nextImage = p.nextImage;
Without seeing your code I think there might be some confusion as to variable scope, as well as class / object variable names. All in all this code is very hard to read, and impossible (for me) to figure out what it is you are trying to do.
I'd say go for that book.
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DarkKitten wrote: I wrote a game emulator with C#..
I find that hard to believe. If that is true, you've learned some things, but missed some basics. Go back and buy that book.
DarkKitten wrote: and plugin is the Class.cs that contains information, like the public int for what the Start Image number is, the Extention of the image, ect..
So, it's reset to 0 every time because you create a new object. Again, buy a book.
Christian Graus
Driven to the arms of OSX by Vista.
Read my blog to find out how I've worked around bugs in Microsoft tools and frameworks.
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Hi
How can i use a function in classes when that function exist in codebehind of a form ?
and :
I use -private void checkBox1_CheckedChanged(object sender, EventArgs e)- in codebehind;
Now i want to use checkBox1_CheckedChanged in another event again;
but compiler doesn't allow me and compiler error me that argument is necessary.
What should i do?
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You must pass the correct argument to the method or of course you'll get compiler errors.
A better approach may be to create a method that can be called from the CheckChanged event
I know the language. I've read a book. - _Madmatt
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Use checkBox1_CheckChanged(Methis, EventArgs.Empty); to call that method
As for
farokhian wrote: How can i use a function in classes when that function exist in codebehind of a form ?
Those are partial classes and can be called as any other function provided the form exists.
Edit: Sorry about the Me, it's been a long day.
modified on Tuesday, November 10, 2009 3:44 PM
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Only ASP.NET has codebehind.
You should post code and the actual error message so we can work out what you mean. Use this and EventArgs.Empty to call an event, but I think it makes more sense to factor out the common code to a method.
Christian Graus
Driven to the arms of OSX by Vista.
Read my blog to find out how I've worked around bugs in Microsoft tools and frameworks.
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hi
after i unzip file and try to copy him, i get error process is used
by another program
what can be the problem ? (work on WinForm - C#)
ZipInputStream sampleInputStream = new ZipInputStream(File.OpenRead(UnZIP_ZipFile));
ZipEntry sampleFile = null;
string sampleOutputDirectoy = UnZIP_RegFile;
int sampleSize = 2048;
sampleInputStream.Password = "12345";
while ((sampleFile = sampleInputStream.GetNextEntry()) != null)
{
sampleSize = 2048;
if (Path.GetFileName(sampleFile.Name) != string.Empty)
{
string sampleFilePath = sampleOutputDirectoy + @"\" + sampleFile.Name;
FileStream sampleFileStream = File.Create(sampleFilePath);
byte[] sampleFileData = new byte[sampleSize];
while (true)
{
sampleSize = sampleInputStream.Read(sampleFileData, 0, sampleFileData.Length);
if (sampleSize > 0)
sampleFileStream.Write(sampleFileData, 0, sampleSize);
else
break;
}
sampleFileStream.Close();
sampleFileStream.Dispose();
}
}
sampleInputStream.Close();
sampleInputStream.Dispose();
MessageBox.Show(" ");
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