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Hi Luc,
Your reply is great! However I do not fully agree with two more comments.
1.
Luc Pattyn wrote: there is no such thing as global variables in OO
We can have global/static variables in C#. I think such kinds of variables are exception to your thread-touched live rule. Means, those global/static variables will always live from process begin to process ends. Any comments?
2.
Luc Pattyn wrote: proves that you cannot simply walk the heap and decide about live and dead for objects,
since doing so would keep A and B alive no matter what.
I do not agree. I think we can still prove A and B are dead since we can not touch them from any threads. Why do you think we can not prove anything? 
regards,
George
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Hi George,
1.
yes, static data members of a class are globals once the class got loaded, and as such
they remain alive as long as the class does; which is as long as the AppDomain does where
the class got loaded; which is until you unload the AppDomain. (By default there is just
the one AppDomain, and you may not even be aware of it).
So, yes, all these static members form another base for the GC the look for live objects.
I see you are getting the picture quite well.
2.
if you were to try and prove the island formed by objects A and B is reachable/unreachable
(and hence alive/dead), you would have to build the entire reference graph and study its
connectivity. If you find several loose groups, you would still have to find out which
groups are reachable (from the stack and the globals) and which are not. Simply looking
at four objects interconnected two-by-two (i.e. A---B and C---D) cannot possibly tell
you which group is alive or dead. So there is nothing much to be gained by studying the
heap itself.
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Thanks Luc,
1.
In your sample before,
--------------------
Final remark: the cyclic reference example I gave earlier (A holds ref to B, B holds ref to A,
none of the threads knows about the existence of A and B, hence both A and B are dead)
--------------------
Do you mean we can not identify whether A and B are live or not? Why we can not identify? I think from your algorithm, at the beginning, mark all objects as dead, then if no variables refer A or B, they will be dead. It is easy to jusge live and dead in the situation you mentioned above, why you think we can not judge?
2.
In C# all the variables must be wrapped in class {}, so it is why you think there is no global variable in C# -- all belong to class context?
regards,
George
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Hi George,
you somehow misunderstood a few things.
1.
the algorithm I described will perfectly judge live/dead on a A---B cluster.
What I said or meant to say is it would not be sufficient to just look at the objects
themselves, you really need to start looking from the known world i.e. stacks and globals.
2.
a class is not an object, a class is not alive; it is either loaded and initialized, or not.
As soon as the class got initialized all static members that have initializers have been
created and are alive (until the class, hence AppDomain, gets removed).
Luc Pattyn [Forum Guidelines] [My Articles]
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Thanks Luc,
Two more comments.
1.
Luc Pattyn wrote: 1.
the algorithm I described will perfectly judge live/dead on a A---B cluster.
What I said or meant to say is it would not be sufficient to just look at the objects
themselves, you really need to start looking from the known world i.e. stacks and globals.
I understand your points now. Your points are, we should not just look at the object themselves, but also whether there are live stack/static variables refer to them, right?
If yes, I think from your algoriothm, cyclic referenced dead variables could be detected, since no one refers to either A or B, right?
2.
Luc Pattyn wrote: 2.
a class is not an object, a class is not alive; it is either loaded and initialized, or not.
As soon as the class got initialized all static members that have initializers have been
created and are alive (until the class, hence AppDomain, gets removed).
Sorry, I have not made my question clear. My points is, all the variables in C# must be defined into class brackets -- { and }, e.g. we can not define a variable outside class brackets into namespace brackets directly, right?
regards,
George
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Hi George,
yes to all.
there are no variables in a namespace, just types (classes, structs, ...)
all variables are inside classes, i.e. when non-static they are inside an object (= an instance
of that class); and when static they are "global" i.e. they are not inside another object,
so you access them (if public) with classnmame.varname so you don't need a reference to
anything, just names.
Luc Pattyn [Forum Guidelines] [My Articles]
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Cool, Luc.
So, the conclusion for this dicussion is, roots (or say, object instances pointed by rules) must be live. Right?
regards,
George
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Hi all,
I want to use FileStream.Read method to read a file but I want it in such a way that I will read a chunk of the whole file instead of reading it all at once.
For instance, I want to read 1KB of data (out of the 1MB), and say do something to that 1KB then proceed to the next 1KB.
Please advise. Thanks!
It is said that the most complex structures built by mankind are software systems. This is not generally appreciated because most people cannot see them. Maybe that's a good thing because if we saw them as buildings, we'd deem many of them unsafe.
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huh?! FileStream.Read works exactly like that! Did you even look at the documentation?
"Reads a block of bytes from the stream and writes the data in a given buffer."
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Woops, yeah, I've looked at the documentation at MSDN. I've figured it out eventually.
It is said that the most complex structures built by mankind are software systems. This is not generally appreciated because most people cannot see them. Maybe that's a good thing because if we saw them as buildings, we'd deem many of them unsafe.
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I have a class called Category which extends ToolStripMenuItem. It also overrides ToolStripMenuItem' ToString method via "new public string ToString () {}". I have an array of Categories and I add them to the combobox: this.cmb_categories.Items.AddRange (categories);
But when I show the form there's two items in the list like there should be but there's no text. I also have a button, that when click calls the ToString method of the selected category but I keep getting a NullReferenceException. I've tried calling Update(), Invalidate(), PerformLayout () and Refresh () on the combo box but it's not working. I've also tried switching from .Net 3.5 to .Net 2.0 but that's not working either.
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Jordanwb wrote: It also overrides ToolStripMenuItem' ToString method via "new public string ToString () {}".
That is a contradiction, it is either override or new. And it seems you want override.
Have it return a constant (say return "aha";) to convince yourself it gets called.
Luc Pattyn [Forum Guidelines] [My Articles]
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- the quality and detail of your question reflects on the effectiveness of the help you are likely to get;
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Tried "public override string ToString ()" and it doesn't work either. Still wouldn't explain the NullReferenceException.
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The NullRefExc has nothing to do with the .NET version, it indicates there is a bug in
your code. Either single-step through it, or look at the Exception.ToString() output
to pinpoint the exact line that causes it.
And publish the Exception as well as (the relevant parts of) your code here if you want
detailed help.
Luc Pattyn [Forum Guidelines] [My Articles]
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- the quality and detail of your question reflects on the effectiveness of the help you are likely to get;
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I'm no longer getting the NullReferenceException for some strange reason, but if I use "new public string ToString ()" or "public override string ToString ()", text isn't showing up in the ComboBox.
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I need to see some code in order to have a chance helping you any further.
Did you single-step the relevant code? did you look at intermediate results?
Luc Pattyn [Forum Guidelines] [My Articles]
This month's tips:
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- the quality and detail of your question reflects on the effectiveness of the help you are likely to get;
- use PRE tags to preserve formatting when showing multi-line code snippets.
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Okee Dokey.
Category class (irrelevant code ommitted)
<code>
public class Category : ToolStripMenuItem
{
public Category(int id, string name)
{
this.id = id;
this.Text = name;
this.sub_items = new List<Program>();
}
public override string ToString()
{
return this.Text;
}
}
</code>
Where I add the Categories to the ComboBox:
<code>
public partial class RemoveCategory : Form
{
public RemoveCategory(AccessReader database, HashMap<int, Category> categories)
{
InitializeComponent();
this.database = database;
this.categories = categories;
this.cmb_categories.Items.AddRange(categories.ToArray());
this.cmb_categories.SelectedIndex = 0;
}
}
</code>
The HashMap class is a class that I made that maps a key (in this case int) to a value (in this case Category), the ToArray() method returns an array of Categories that contain all the values in the HashMap. In the callback for when the button is clicked, the SelectedItem property of the ComboBox is no long returning null but is returning an object which is casted into a Category.
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Hi,
you have a problem in the button click handler, but you don't show its code.
you explain about HashMap but the code you show does not use it.
you had null exceptions but they are gone without any explanation? or are they still present?
are you sure you want to be successful in software development?
start by giving all relevant code, exactly as it is, and all the symptoms, and please
combine them in a single message, to increase the possibility they describe a consistent
situation.
Luc Pattyn [Forum Guidelines] [My Articles]
This month's tips:
- before you ask a question here, search CodeProject, then Google;
- the quality and detail of your question reflects on the effectiveness of the help you are likely to get;
- use PRE tags to preserve formatting when showing multi-line code snippets.
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Luc Pattyn wrote: you have a problem in the button click handler, but you don't show its code.
you explain about HashMap but the code you show does not use it.
you had null exceptions but they are gone without any explanation? or are they still present?
are you sure you want to be successful in software development?
start by giving all relevant code, exactly as it is, and all the symptoms, and please
combine them in a single message, to increase the possibility they describe a consistent
situation.
It's hard to have a consistent solution if the program isn't acting consistantly (flashbacks to Java). The HashMap class is irrelevant to the problem. In the Button click event I am no longer getting the NullReferenceException.
Here's the button click event:
<br />
private void btn_okay_Click(object sender, EventArgs e)<br />
{<br />
try<br />
{<br />
Category s = (Category)cmb_categories.SelectedItem;<br />
MessageBox.Show(s.ToString());<br />
}<br />
catch (NullReferenceException nre)<br />
{<br />
MessageBox.Show(nre.ToString());<br />
}<br />
}<br />
What is there to go wrong there on my end? Yesterday cmb_categories.SelectedItem was returning null, now it's not. I get a MessageBox saying "Office" or "Programming" like it should, so that would mean no NullReferenceException. The HashMap returned a proper array of Categories, no nulls whatsoever.
Also in the constructor I added this line directly after "this.cmb_categories.Items.AddRange(categories.ToArray());":
ComboBox.ObjectCollection oj = cmb_categories.Items;
oj.Count said 2, which is correct. I place a breakpoint at the line mentionned above and it reaches that line I hover over oj, then hover over "Non Public Members", then over "innerList" it shows two objects both of type Category, and the proper ToString() method of the two categories were called.
Luc Pattyn wrote: you explain about HashMap but the code you show does not use it.
Yes I did, check the constructor's parameters. I called it a HashMap because that's what it's called in Java. Until today I learned that C# has one in System.Collections.Generic, it's called a Dictionary.
Luc Pattyn wrote: are you sure you want to be successful in software development?
Who said I wanted to go into software development? I plan on going into PHP based website design.
Oh BTW, I had a similar problem with a ListBox I believe. I had one form with said ListBox, I had two different classes extend that form. On one form the add worked whereas on one class it did not. In the parent form I had a method to do an invoke to avoid the CrossThreadedCallException. Both child classes used the same method. Then for some reason the second started working for no reason whatsoever. Was that my fault? I've seen this happen dozens of times: code just starts working with everyone scratching their heads.
modified on Sunday, April 20, 2008 10:13 PM
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Hi,
I missed the relevance of HashMap due to your way of publishing code; instead of showing
real < and > signs you insert something that results in escape sequences, and instead
of using real PRE tags you use fake CODE tags; this makes reading your stuff rather hard.
If the combobox does not show the right stuff and it gets populated by an
AddRange(categories.ToArray()) then either your observation is wrong or
the ToArray() method does not function properly, which is what I expect. I don't know
what your ToArray() returns, but combobox expects either a list of strings, or a list
of items that can be displayed by calling their ToString().
Just logging the ToArray() result should pinpoint the problem.
I do not like your attitude on things that first don't work, then suddenly do work.
If "code just starts working with everyone scratching their heads" then something is
definitely wrong; it could be your PC hardware or software; more likely it is a
lack of quality and robustness in your code, something that you must learn by
investigating problems until you SOLVE them, and not until they happen to disappear.
I leave this thread here and now, its length exceeds its weight. 
Luc Pattyn [Forum Guidelines] [My Articles]
This month's tips:
- before you ask a question here, search CodeProject, then Google;
- the quality and detail of your question reflects on the effectiveness of the help you are likely to get;
- use PRE tags to preserve formatting when showing multi-line code snippets.
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Luc Pattyn wrote: I missed the relevance of HashMap due to your way of publishing code; instead of showing
real < and > signs you insert something that results in escape sequences, and instead
of using real PRE tags you use fake CODE tags; this makes reading your stuff rather hard.
Whoa there, that was the forum. As soon as I put in the < and > the forum changed them to the HTML escape characters.
Luc Pattyn wrote: If the combobox does not show the right stuff and it gets populated by an
AddRange(categories.ToArray()) then either your observation is wrong or
the ToArray() method does not function properly, which is what I expect. I don't know
what your ToArray() returns, but combobox expects either a list of strings, or a list
of items that can be displayed by calling their ToString().
The AddRange method accepts an array of objects not strings. I did:
Category[] all_categories = categories.ToArray (); and it returned an array of Categories like I expected.
Luc Pattyn wrote: I do not like your attitude on things that first don't work, then suddenly do work.
Well sorry for telling it like it is. That's what happened.
Luc Pattyn wrote: If "code just starts working with everyone scratching their heads" then something is
definitely wrong; it could be your PC hardware or software; more likely it is a
lack of quality and robustness in your code, something that you must learn by
investigating problems until you SOLVE them, and not until they happen to disappear.
It's hard for simple, incredibly short code to be inefficient and unrobust. It's also hard for it to be my fault when it is adding them to the comboBox but not showing the actual text in the comboBox.
Luc Pattyn wrote: I leave this thread here and now, its length exceeds its weight.
Okay fine.
Maybe if I retype everything a fourth time it will magically start working.
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Hi,
I started to use c# for sometime and I don't have any certification of Microsoft. Can anyone please recommend the first certificate for me. thk in advance.
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You need to decide what you want to focus on in the industry. If you are into C# you probably want to do the VS2005 or VS2008 training which include either Microsoft Certified Professional Developer and Microsoft Professional Technology Specialist. Within those two it breaks down whether you want to be a web developer, Windows developer and so forth. I have posted a Microsoft link that will probably help. Once you know which route you want to take then start at the lowest level class.
http://www.microsoft.com/learning/mcp/certifications.mspx[^]
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You can start with 70-536 Application Foundation. It's for .Net 2.0.
If you just started C# you should wait and read a few books since this exam covers a lot of things.
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Hey everyone
I can successfully use SendInput to send mouse clicks, but I am having trouble getting it to work with sending keys. Please can someone tell me where I have gone wrong
public struct KEYDBINPUT
{
public Int16 wVk;
public Int16 wScan;
public Int32 dwFlags;
public Int32 time;
public Int32 dwExtraInfo;
public Int32 __filler1;
public Int32 __filler2;
}
public struct INPUT
{
public Int32 type;
public KEYDBINPUT ki;
}
[DllImport("user32")]
public static extern int SendInput(int cInputs, ref INPUT pInputs, int cbSize);
public const int INPUT_KEYBOARD = 1;
public const int KEYEVENTF_KEYUP = 0x0002;
public void sendKey(short key)
{
INPUT inputDown = new INPUT();
inputDown.type = INPUT_KEYBOARD;
inputDown.ki.dwFlags = 0;
INPUT inputUp = new INPUT();
inputUp.type = INPUT_KEYBOARD;
inputUp.ki.dwFlags = KEYEVENTF_KEYUP;
inputDown.ki.wVk = key;
SendInput(1, ref inputDown, Marshal.SizeOf(inputDown));
inputUp.ki.wVk = key;
SendInput(1, ref inputUp, Marshal.SizeOf(inputUp));
}
Thanks a lot
Luke
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