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Hi there!
Recently I encountered a surprising effect of the C# language. I wrote the following lines:
public class A
{
public string name;
}
public class X
{
public static void Main()
{
A a1 = new A();
A a2 = new A();
A a;
A _a;
a = a1;
_a = a;
_a.name = "TTT";
//ok, variable "a1" is modified
a = a2; //change the reference target to instance "a2"
_a.name = "SSS";
//?!?, still variable "a1" is modified, although
//the reference is pointing to variable "a2" !!!
_a = a;
_a.name = "SSS";
//ok, now variable "a2" is modified
}
Om, what's happening here? It should be possible to create references to a reference in C#? Is there any optimization action done in the background, that translates a "ref to ref" to a "ref", what would explain the ignoring of the changed ref variable?
Greetings,
Matej
}
Balkanese
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A Reference is just a fancy word for a pointer. Consider...
A a1 = new A();
A a2 = a1;
A a3 = a2;
So everything is pointing to the same instance of the class A
Now...
a2 = new A();
What do you think happens? ...
a1 still points to the first instance
a2 now points to the second instance
a3 still points to the first instance
Why? Because a3 was never told to point to anything else. When a3 was created it was told to point to the first instance, not to a2 - In other words it was told to point to whatever a2 was currently pointing to. a2 is still at liberty to point to something else in the future.
Does this help clear things up?
--Colin Mackay--
"In the confrontation between the stream and the rock, the stream always wins - not through strength but perseverance." (H. Jackson Brown)
Enumerators in .NET: See how to customise foreach loops with C#
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Yes, thank you!
I was assuming something like this. So this means there is no way to let a reference point to a reference instead to the instanced object itself in C#, like it was possible in C++?
This would be a great thing e.g. for a list (ArrayList, etc.). If the listelements would point to a reference variable not to an instance I would just have to change that ref variable in order to change all list elements with that target at one time!
But it seems, that if I want to do so, I will have to change the instantiated object itself, won't I?
Matej
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Why does VS.NET 2003 delete everything from the debug directory, when building a solution? I can't run my application, because when I build it, app.exe.config is removed from the debug directory.
Please HELP
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This is the behavior of practically any build system - it removes the old stuff. VS.NET does have an undocumented (at least, from what I've read) feature where any file named app.config in your project gets renamed appropriately and moved to your target output directory. You could either add this file to your project and make sure the settings are correct in that, or have a backup app.exe.config file in your target output directories that you can copy to the appropriate name after building.
-----BEGIN GEEK CODE BLOCK-----
Version: 3.21
GCS/G/MU d- s: a- C++++ UL@ P++(+++) L+(--) E--- W+++ N++ o+ K? w++++ O- M(+) V? PS-- PE Y++ PGP++ t++@ 5 X+++ R+@ tv+ b(-)>b++ DI++++ D+ G e++>+++ h---* r+++ y+++
-----END GEEK CODE BLOCK-----
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If you have a "myapp.exe.config" file in your output folder (e.g. "Debug"), VS.NET tries to replace it with one within your project directory, if it doesn't find it, it deletes it. You can avoid this by making it read-only.
But the better solution is:
-Add an "app.config" (exactly this name) to your VS.NET project. Use it as your configuration file.
- Now everytime you change this file and build your project, it gets copied as "myapp.exe.config" into the output folder.
--
- Free Windows-based CMS: www.zeta-software.de/enu/producer/freeware/download.html
- See me: www.magerquark.de
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I want a control that is based off the Panel control, I would like to be able to drag and drop items on this the same way that i can for the Panel on the toolbox. when i create this custom control it's design view is that of a control that you can not drag and drop things on it.
how can i get my custom panel control to act and feel like the base Panel that comes out of the box?
thanks
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What do you mean, ...based off the Panel control...? Do you mean you extended it? This should work if you did because the designer usually uses the designers from classes up the class chain. Hmm. If nothing else, use ildasm.exe to find out the what Type the DesignerAttribute of the Panel class uses, and use that same attribute (specifying the same Type, which is probably a string representation, but if not it will use the typeof statement) to attribute your class.
You could also implement your own designer than enables drag and drop - and filter the types of controls that can be added - by reading the docs on the DesignerAttribute and the IDesigner interface, although it's typically easier to start off (i.e., extend) with a root designer class, like the ParentControlDesigner, which has support for controls that contain nested controls (like you want).
-----BEGIN GEEK CODE BLOCK-----
Version: 3.21
GCS/G/MU d- s: a- C++++ UL@ P++(+++) L+(--) E--- W+++ N++ o+ K? w++++ O- M(+) V? PS-- PE Y++ PGP++ t++@ 5 X+++ R+@ tv+ b(-)>b++ DI++++ D+ G e++>+++ h---* r+++ y+++
-----END GEEK CODE BLOCK-----
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Hello,
I have a C# application I want to speed up.
Does anybody know a tool to monitor it and tell me in which part of the process it spends its time ?
Thanks
Callixte.[^]
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The CLR Profiler (v2.0)[^] might be of some help, give it a try.
-Nick Parker
Last time I checked, all programmers have selective ignorance. I know nothing about 3D graphics. I know a lot about COM. VB gets under people's skin because one can be ignorant of computer architecture and ASM and still get a lot done. - Don Box
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This is propably a question from which everyone should know the answer, but I want to ask it anyway. 
If I have an enum, like this:
[Flags]
public enum ThisIsAnEnum
{
None,
FirstFlag,
SecondFlag,
ThirdFlag,
FourthFlag
}
How do I test whether a specific value is used?
Is this the proper way?
ThisIsAnEnum enumValue = ThisIsAnEnum.SecondFlag | ThisIsAnEnum.FourthFlag;
if (enumValue & ThisIsAnEnum.SecondFlag != 0)
{
}
Or is there some method like Flags.Match(), but for a bitfield value?
And why do I have to add the values of the enum to it's members? Like this:
[Flags]
public enum ThisIsAnEnum
{
None = 0,
FirstFlag = 1,
SecondFlag = 2,
ThirdFlag = 4,
FourthFlag = 8
}
If I don't, their values will be 0, 1, 2, 3, 4, 5, 6..., and not 0, 1, 2, 4, 8, 16... .
Thanks in advance,
- Daniël Pelsmaeker
The earth is not dying. it is being killed...
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Daniël Pelsmaeker wrote:
Is this the proper way?
ThisIsAnEnum enumValue = ThisIsAnEnum.SecondFlag | ThisIsAnEnum.FourthFlag;if (enumValue & ThisIsAnEnum.SecondFlag != 0){ // Do something...}
Close:
ThisIsAnEnum enumValue = ThisIsAnEnum.SecondFlag | ThisIsAnEnum.FourthFlag;
if ((enumValue & ThisIsAnEnum.SecondFlag) != 0)
{
}Putting the bitwise & statement in its own pair of parens is necessary due to operator precedence.
-----BEGIN GEEK CODE BLOCK-----
Version: 3.21
GCS/G/MU d- s: a- C++++ UL@ P++(+++) L+(--) E--- W+++ N++ o+ K? w++++ O- M(+) V? PS-- PE Y++ PGP++ t++@ 5 X+++ R+@ tv+ b(-)>b++ DI++++ D+ G e++>+++ h---* r+++ y+++
-----END GEEK CODE BLOCK-----
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Thank you very much.
- Daniël Pelsmaeker
"The secret of a successful restaurant is sharp knives."
- George Orwell [pseud. of Eric Arthur Blair]
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[Flags] is merely an attribute that's put on enums - it doesn't change the compiler behavior. We don't automatically switch to powers of two because people often want to define combinations of flags, and what was going on would be much less clear if that was the case. Ditto for looking at the numeric values someplace and having to translate back to the identifiers.
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Okay, but what use is the Flagsattribute then? If I'm not mistaken, I can add enum values together using |, even when I didn't set the Flagsattribute.
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[Flags] isn't really a compiler thing. It's used by object browsers to tell people what kind of enumeration it is, and Enum.ToString() bases its behavior on whether [Flags] is present.
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i have written the code to transfer image file through sockets. Below is the code for client. It just runs and exit nothing happens. Can anybody help?
In this code first i get the file size then the actual file through bytes.
using System;
using System.Net.Sockets;
using System.IO;
using System.Threading;
namespace ImageClient
{
///
/// Summary description for Class1.
///
class Class1
{
bool flag = true;
Socket clientSocket;
AsyncCallback pnfCallback = null;
int fileSize;
byte[] buffer = new byte[1024];
///
/// The main entry point for the application.
///
[STAThread]
static void Main(string[] args)
{
Class1 c = new Class1();
c.clientSocket = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
System.Net.IPEndPoint ipend = new System.Net.IPEndPoint(System.Net.IPAddress.Parse(args[0]),8221);
c.clientSocket.Connect(ipend);
c.WaitForData();
}
public void WaitForData()
{
if(pnfCallback == null)
{
pnfCallback = new AsyncCallback(onDataReceived);
}
IAsyncResult result = clientSocket.BeginReceive(buffer,0,buffer.Length,SocketFlags.None,pnfCallback,null);
}
public void onDataReceived(IAsyncResult result)
{
if(flag)
{
int count = clientSocket.EndReceive(result);
char[] chars = new char[count];
System.Text.Encoding.Default.GetDecoder().GetChars(buffer,0,count,chars,0);
fileSize = int.Parse(new string(chars));
Console.WriteLine("Got the buffer " + fileSize);
Console.ReadLine();
flag=false;
buffer = null;
buffer = new byte[fileSize];
WaitForData();
}
else
{
clientSocket.EndReceive(result);
FileStream fs = new FileStream("c:/def.gif",FileMode.Create);
fs.Write(buffer,0,buffer.Length);
fs.Flush();
fs.Close();
WaitForData();
}
}
}
}
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Well, You are using an Asyncronous callback which means that the function will return immediately without waiting for the data to be received. Once the data is received the your callback method (onDataReceived)will be invoked. However, because your application has exited before the data is received the callback method will never be invoked and so no data will received either.
--Colin Mackay--
"In the confrontation between the stream and the rock, the stream always wins - not through strength but perseverance." (H. Jackson Brown)
Enumerators in .NET: See how to customise foreach loops with C#
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How to load a C# windows application from a c# window service.Plse suggest if it is possilble and how.
Thanks in advance
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I don't know what do you mean by "..load win. app..".
1. Do yu mean a COM object? Yes it's possible by using COM Interop
2. Do you mean an external application? It's possible by System.Diagnostics.Process.Start("your.exe");
3. Or do you mean to have external app. which communicate with Win seprvice application? It's possible by .NET remoting...
Could you be more specific?
Tomas Rampas
------------------------------
gedas
System analyst, MCSD
TGM 840,
293 01 Mlada Boleslav,
Czech Republic
rampas@gedas.cz
http://www.gedas.com/
------------------------------
To be or not to be is true...
George Bool
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Thank you Rampas Tomas and sorry for the confusion,I mean an external windows application, I will try with System.Diagnostics.Process.Start("your.exe");
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Hi,
I want to create a GUI similar like all the media player's (skins). The graphics are not the problem but the GUI must be sizeable. Is there somewhere a description or sample with how-to?
Cheers Gaby
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Hi all,
If I call
g.DrawRectanlge(
new SolidBrush( Color.Blue ),
new Rectangle( 0, 0, this.Width, this.Height ) );
// in my control OnPaint()
Why is it that the right and bottom line paint one pixel outside the control?
Like if I specify a Rectangle( 0, 0, 200, 200 ), and draw it,
it draws a line down pixel x = 0, and across y = 0, good. Then down x = 200, and across y = 200. 200 is suppose to be the width and height, so the last 2 lines should be down x = 199, and across y = 199.
Has anyone else ever noticed this?
When I am drawing mulitple rectangles side by side like:
for( int i = 0; i < 7; ++i )
{
g.DrawRectangle( brush, bounds );
bounds.X += bounds.Width;
}
The lines in between the boxes are drawn over top of each other, so it looks like one line, one pixel thick.
In order for me to have the correct boxes (each has its own outline):
for( int i = 0; i < 7; ++i )
{
g.DrawRectangle( brush,
new Rectangle( bounds.X, bounds.Y,
bounds.Width - 1, bounds.Height - 1 ) );
bounds.X += bounds.Width;
}
Does anyone know the reason why this happens? What is the logic behind drawing it this way?
Thanks for any insight into this,
Kris.
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The coordinate system
As we all know, drawing systems in .Net are based upon pixels that are arranged on a two-dimensional coordinate system. The origin, that is, the points (0, 0) lie on the far top-left of the screen. Each consecutive pixel towards the right of the origin forms the x-axis, and each consecutive pixels towards the bottom of the screen forms the y-axis.
If you note carefully, the co-ordinate system for onscreen graphics is an inverted copy of the Cartesian Co-ordinate System used in Mathematical Geometry.
Now, when we give the call to the system to draw a rectangle, we provide it with four arguments. The x-coordinate, the y-coordinate, width and the height of the rectangle. We will traverse through each step that the system undergoes to create a rectangle.
Step 1:
First, the point (x, y) or the pixel present on the point (x, y) is plotted or marked on the coordinate system as shown below.
Step 2:
Then, it adds the width provided as argument to the next consecutive x-coordinate. For instance, if the x-coordinate is 0 and the width is 10, then the resultant point on the x-axis (fx) will be:
Because x-coordinate specified was 0,
So the next x-coordinate will be 1
Final Point = next x-coordinate + width
Final Point = 1 + 10
Final Point = 11;
Same goes for the y-coordinate and the height to calculate the resultant point on the y-axis (fy).
Step 3:
System marks all the pixels from (0, 0) to the point (fx, 0) on the x-axis and also marks all the pixels from (0, 0) to (0, fy). This gives two straight lines joined at (0, 0) at an angle of 90 degrees.
The points (fx, 0) and (0, fy) are then interconnected at the point (fx, fy). Thus giving the illusion of a perfect rectangle.
What happens with GDI+ drawing routines
If you keep the x-coordinate and the y-coordinate as (0, 0), then it is seen that:
Resultant Point fx = width + 1 and
Resultant Point fy = height + 1
So, if we specify the below mentioned statements in GDI+:
g.DrawRectangle(new SolidBrush(Color.Blue), 0, 0, this.Width, this.Height);
g.DrawRectangle(new SolidBrush(Color.Blue),
new Rectangle(0, 0, this.Width, this.Height));
From these statements, it is clear that the resultant point to which the rectangle will be stretched is (this.Width+1, this.Height+1) which unfortunately exceeds the visible region of the Component or Custom Control.
Did not understand a single word? Ask for a detailed and illustrated description at: aaronreginald@yahoo.com. I would be more that glad to help you out.
The beginning of knowledge is the fear of God
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