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If there's just a single event handler attached, then it's fairly easy:
In your class you need:
public delegate MyCancelHandler(bool cancel);
public event MyCancelHandler AnEventThatCanBeCancelled;
if (AnEventThatCanBeCancelled != null)
{
bool cancel = false;
AnEventThatCanBeCancelled(cancel);
if (cancel)
{
MessageBox.Show("Event has been cancelled by a listener");
}
else
{
MessageBox.Show("Event has NOT been cancelled, go on with whatever you want");
}
}
If there's more than one listener attached, then you'll only get the cancel info of the last listener notified.
In this case you'll have to go through all registered delegates (using MulticastDelegate.GetInvocationList()) and check all of them if anyone wants to cancel your event.
Regards,
mav
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That won't work. bool (System.Boolean) is a value type, and you'd need to declare the delegate parameter as out or ref.
Besides, it's far easier to just reuse CancelEventHandler. Since it uses the CancelEventArgs which has a Cancel property (that will keep the value), you don't need to declare your own event.
Also, while it's not required, events should typically follow the EventHandler signature and the second parameter should (agian, not required to) derive from EventArgs. CancelEventArgs does, of course, extend this class.
If you want to know what a specific callee of the callback set the CancelEventArgs.Cancel property to, your past paragraph is correct.
Microsoft MVP, Visual C#
My Articles
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Of course you're right, Heath.
This is what you get when you don't actually try out your own suggestions...
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Hi,
I have two different type of designers e.g. a flowchart designer and a form designer, how should i integrate them in one enviroment. As each designer has its own toolbar (having different tools) and its own properties (shown in propertygrid).
What is the best approach to go with.
Thanks in advance,
Omar Rehman
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Hi all
The help is necessary. I need in my program climb on https site.
a problem in that that it is necessary to establish the certificate from this site.
The request to those who worked with it to to give a slice of a code for work with
certificates (it'll be good if it be working)
everyone speak that X509Certificate must be used but in msdn there is no real code.
please help because I burn
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There isn't always sample code in MSDN, so you must understand how to use the types that are documented. HttpWebRequest.ClientCertificates is an X509CertificationCollection, so obviously you need to instantiate that collection class. Since it's also an IList implementation, you can add and remove X509Certificates.
If you already have client certificates (which you can view and export in the Internet Options, Content tab), you can simply use the static X509Certificate.CreateFromCertFile method, passing the filename of the client certificate for identification to the server that you can export from Internet Options like I mentioned above.
Microsoft MVP, Visual C#
My Articles
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please give me some code if you have because i can write it by myself!!!
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I am trying to receive the udp datagram that from
the client sended to the server port 7090,but i have some questions following.
1) How to listen to port 7090?
Should I setup a timer to scan port 7090?
2) Is there a event that start when the udp
datagram get to the server and how to
implement?
3) If many client send to the same server port 7090 in the same time.
How can I to sure which one is from where?
thanks for your help!
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UdpClient.Receive is a blocking call, and there is no events on the UdpClient. You use it to send packets to a server or multicast group and then call UdpClient.Receive to wait for a response.
You should read the class documentation[^] for the UdpClient in the .NET Framework SDK. It contains all the information you should need plus many examples of how to use it.
Microsoft MVP, Visual C#
My Articles
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can someone tell me how I can get the code below to paint the rectangle where the button is(even though it is not behind drawn(this is code to show an example of a problem I'm having, I don't want to make button invisible)... it seems that the base class has introduced a clip region where the button is. I've tried my best to remove this region(messing with the painteventargs clip region, getting a graphics object from this.CreateGraphics, etc...)... I've also tried to remove the WM_CLIPSIBLINGS from the CreateParams, but that didn't work... not sure if this is a bug in forms or I'm just missing something. Anyways, I really hope someone can help me as this is my 3rd post on this. Thanks.
using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.Button button1;
private System.ComponentModel.Container components = null;
public Form1() { InitializeComponent(); }
protected override void Dispose( bool disposing )
{
if ((components != null) && (disposing)) components.Dispose();
base.Dispose( disposing );
}
#region Windows Form Designer generated code
private void InitializeComponent()
{
this.button1 = new System.Windows.Forms.Button();
this.SuspendLayout();
//
// button1
//
this.button1.Location = new System.Drawing.Point(96, 64);
this.button1.Name = "button1";
this.button1.Size = new System.Drawing.Size(136, 136);
this.button1.TabIndex = 0;
this.button1.Text = "button1";
//
// Form1
//
this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
this.ClientSize = new System.Drawing.Size(292, 273);
this.Controls.Add(this.button1);
this.Name = "Form1";
this.Text = "Form1";
this.ResumeLayout(false);
}
#endregion
[STAThread]
static void Main() { Application.Run(new Form1()); }
protected override void OnPaintBackground(PaintEventArgs e)
{
e.Graphics.FillRectangle(new SolidBrush(this.BackColor), 0, 0, Width, Height);
}
protected override void WndProc(ref Message m)
{
if (m.Msg == 0x000F)
{
return;
}
base.WndProc (ref m);
}
}
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It's not a good idea to simply ignore WM_PAINT (0x000f). Instead, add the following to your constructor:
SetStyle(ControlStyles.AllPaintingInWmPaint |
ControlStyles.DoubleBuffer | ControlStyles.UserPaint, true); This forces double-buffered painting to occur all within your OnPaint override. See the ControlStyles enumeration documentation in the .NET Framework SDK for more information.
Microsoft MVP, Visual C#
My Articles
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this doesn't seem to work because I want to do all the double buffering. I do not want the parent at all to do anything for the child controls, not even call them to be painted(well, doesn't really matter)... specially don't want them to draw some black filled rectangles for there background. The only way I can get close to getting what I want is to override the WM_PAINT and in it, call my Painting functions directly. The only problem with this, is when I use the control, I get a flash of the black rectangle. So there must be more window messages that are being called that do this "stupid" thing. I know resize and move does it. I've tried setting what you said in both the form's constructor and the childs and neither work. Not sure why, but the WndProc's base has some code in there that is really screwing things up for me... I don't like to override the WM_PAINT, but seems to be the only probable solution at the moment.
this is the process: In the Main form, create a bitmap and in the OnPaintBackground draw the bitmap to window. In the Controls OnPaint, pass the bitmap to the base controls' OnPaint so we can let windows handle drawing the control to the bitmap(basicaly base.OnPaint(new PaintEventArgs(G, clip)) where G is the graphics object of the bitmap and clip is the clip rectangle)
all this code works smoothly, except for those damn black rectangles over the controls.
Anyways, hopefully you understand the problem? I'm sure theres a simple solution(atleast I hope), and thanks for helping...
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I understand the problem. In your override to OnPaint, just don't call base.OnPaint. In the base class, WM_PAINT is already being caught and OnPaint (indirectly) is being called. In Control.WndProc, after calling the internal WmPaint (which calls OnPaint after some setup code) execution is returned to the caller. Since WndProc is the WindowProc for the window class, WM_PAINT shouldn't be sent to the control without first going through OnPaint, which means you control all painting. As I said before, just don't call base.OnPaint and all the painting is done by you.
There are many articles here on CodeProject about painting your own buttons. If all you're trying to do is avoid having the black rectangle painted, 1) drawing a button yourself (completely) wouldn't be that hard (if you want the raised look, use state variables that you set in the mouse event handlers by overriding the respective OnEventName methods), and 2) you should be able to set the clipping region within your implementation. Since you now control all the painting, you decide what gets drawn and what doesn't.
If you were to set the clipping region this way, then you could eliminate the area that the black border would cover and then call base.OnPaint. OnPaintBackground isn't necessary since setting ControlStyles.AllPaintingInWmPaint to true using SetStyle directs all painting to be done in the WM_PAINT handler.
Microsoft MVP, Visual C#
My Articles
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is there a way to change the max image size to more than 256?
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No. If you want an ImageList-like class to hold more, you'll need to develop your own; but I warn you that this would be very resource intensive.
You might consider, instead, to cache those images to disk since they would require a lot of memory, of which the CLR already requires quite a bit plus the more assemblies you use, the more memory is required (this is true of any application that imports libraries).
Microsoft MVP, Visual C#
My Articles
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hi all,
i'm tring to write a progarm to manage my network cards (wire/wireless).
I want to disable the wire card and enable the wireless (and reverse).
from my research i understand that wmi is not providing this feature, only to disble DHCP or give 0.0.0.0 in the IP.
i need to diable(and enable)throw c#.
does any one know how ?
pls help ASAP.
10x
liron shryer
Nice systems.
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My console project is named UsingConfigSettings in C#, and wanted to store the database connection in an application config file. I added an application config named "UsingConfigSettings.exe.config" in my project. Here is its contents:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
<add key="constring" value="server=localhost;database=Northwind;uid=sa;pwd=;"/>
</appSettings>
</configuration>
I even copied it in the bin\debug folder in my C# console application, but it still doesn't work. I acccess it in the console as:
using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
public class UsingConfigSettings
{
public static void Main()
{
SqlConnection con = new SqlConnection(ConfigurationSettings.AppSettings["constring"]);
SqlCommand cmd = new SqlCommand();
cmd.CommandText = "SELECT * FROM Customers";
cmd.Connection = con;
con.Open();
SqlDataReader reader = cmd.ExecuteReader();
while(reader.Read())
{
Console.WriteLine("{0} - {1}", reader.GetString(0), reader.GetString(1));
}
con.Close();
Console.ReadLine();
}
}
but it won't work, it always issued a message of:
"An unhandled exception of type 'System.InvalidOperationException' occurred in system.data.dll
Additional information: The ConnectionString property has not been initialized."
If I don't use any config file, and replace the code above, it works fine:
SqlConnection con = new SqlConnection("server=localhost;database=Northwind;uid=sa;pwd=;");
Please help.
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If you want the .config file to be copied automatically to the target directory, create a file named app.config in the root of your project. VS.NET will automatically rename this according to your executable name and copy it into the bin\Debug or bin\Release directory along with the application.
Make sure that when you run the application, you are running the one in the target directory. If you hit F5 (debug), the application is actually run out of the obj\Debug directory. Using the method I described above will make sure the .config file is renamed and copied to the obj\Debug directory as well (which is actually the target directory).
Everything else you have is right.
FYI, never use sa without a password! Since you're using SQL, either use SSPI (don't specify uid or password, and instead use Integrated Security=SSPI and add your Windows login username or group to SQL Server), or set up a different user account. Give sa a password anyway. This is like having the administrator account with no password as well - it's a big hole in security.
Microsoft MVP, Visual C#
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I am wrapping a Dll function with managed code and am confused about the equivalent of pointers and the & symbol in C. I am working with two C functions wrapped in a Dllimport:
[DllImport("msg.dll",CharSet=CharSet.Ansi)]
public static extern int MsgConnect (int lAPIVersion, string lpcszTopic, ref OPERATOR lpOperator, ref IntPtr lphContext);
Where the C functional prorotype was:
MSGAPIFUNCTION MsgConnect(long lMsgAPIVersion, const char *lpcszTopic, LPOPERATOR lpOperator, MSGHANDLE *lphContext);
The lphContext is a handle, specified in C as:
typedef void *MSGHANDLE
I am trying to import this function:
MSGAPIFUNCTION MsgStartMessage(MSGHANDLE hContext, const char *lpcszActivityName, const char *lpcszMsgName, int bOriginatorVerified)
I have defined it as:
[DllImport("msg.dll",CharSet=CharSet.Ansi)]
public static extern int MsgStartMessage (ref IntPtr hContext, ref string lpcszActivityName, ref string lpcszMsgName, int bOriginatorVerified);
Note it is using the variable itself, not a pointer to it like the previous prototype. I implemented the pointer as IntPtr, not sure how to implement this - do I need to convert it to an Int?
Thanks in advance.
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Don't use ref or out with reference types (like a string) unless the address of a pointer is required (a pointer to a pointer to an object). So, const char * lpcszActivityName should be declared as string lpcszActivityName, for example.
FYI, you don't need to use the same parameter names. Function call execution uses a stack of parameters and pops parameters based on size. The parameter name is of no consequence when marshaling from managed to unmanaged code. Using ".NET-friendly" parameter names makes the code easier to follow.
Also, hContext should be declared as an IntPtr, not ref IntPtr. As I mentioned the last time, and IntPtr can also represent a memory address (which is a HANDLE, for which MSGHANDLE is a typedef) since it's a system-dependent size.
You really need to understand the difference between reference types (alloc'd on the heap) and value types (alloc'd on the stack; immutable), and understand the data type mapping. See Platform Invoke Data Types[^] for a mapping of basic data types.
Microsoft MVP, Visual C#
My Articles
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it's easy enough to capture a form's closing events when you hit the upper right hand corner X to do cleanup stuff, but
is it also as easy to do it with console applications? there are some things i need to do when i close the console app by
using the upper right hand X, how can i do this?
thanks!
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When you close the command shell, it kills the process. There's really no way to trap this since the console is a different subsystem from Windows, which can send or post messages before it is shutdown.
Microsoft MVP, Visual C#
My Articles
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//CONSTANTS
public const int IS3K_SHORT_DESCRIPTION_MAX = 20 ;
public const int IS3K_LONG_DESCRIPTION_MAX = 50 ;
public const int IS3K_LINE_KEY_MAX = 12 ;
public const int IS3K_LINES_PER_SHOW = 20 ;
//STRUCT DECLARATION
[StructLayout(LayoutKind.Sequential)]
public struct _IS3kLineDescription
{
[MarshalAs(UnmanagedType.ByValArray, SizeConst= IS3K_LINE_KEY_MAX , ArraySubType = UnmanagedType.U1)]
public byte[] LineKey;
[MarshalAs(UnmanagedType.ByValArray, SizeConst= IS3K_SHORT_DESCRIPTION_MAX , ArraySubType = UnmanagedType.U1)]
public byte [] LongDescription;
[MarshalAs(UnmanagedType.ByValArray, SizeConst= IS3K_LONG_DESCRIPTION_MAX , ArraySubType = UnmanagedType.U1)]
public byte [] ShortDescription;
}
[StructLayout(LayoutKind.Sequential)]
public struct _IS3kShowLines
{
public int Command;
public int Flag;
public int TotalLines;
public int TopLine;
[MarshalAs(UnmanagedType.ByValArray, SizeConst= IS3K_LONG_DESCRIPTION_MAX , ArraySubType = UnmanagedType.Struct) ]
public _IS3kLineDescription[] Line;
};
//Implementaion code
_IS3kShowLines showLines = new _IS3kShowLines() ;
_IS3kLineDescription oneLineDescription = new _IS3kLineDescription();
int x,y;
//this one is working ok
y = Marshal.SizeOf(oneLineDescription );
//this one does not,
//as there is array of struct within struct
//program dies.
//An unhandled exception of type 'System.ArgumentException' occurred in
//Additional information: Type _IS3kShowLines can not be marshaled as
//unmanaged structure; no meaningful size or offset can be computed.
x = Marshal.SizeOf(showLines );
Can anyone please tell why second SizeOf does not work
my intention is find out sizeof showLines variable
thanks
Uday Shastri
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Udaynet wrote:
//this one does not,
//as there is array of struct within struct
x = Marshal.SizeOf(showLines );
Can anyone please tell why second SizeOf does not work
That doesn't help. Please be specific. I suspect you're getting an ArgumentException stating that no meaningful information can be retrieved (or something to that effect).
Also, _IS3kShowLines does not need to be declared as unsafe: not only are you not using unsafe code, unsafe code is not necessary in .NET; though, it's useful for times when you want efficient access to direct memory, like pixel processing for large images. This makes your code unverifiable which may or may not lead to deployment problems (based on your deployment scenario) because of .NET CAS (code access security).
Microsoft MVP, Visual C#
My Articles
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Heath Stewart
Hello
To be more specific I get this error
An unhandled exception of type 'System.ArgumentException' occurred in Myapp.exe
Additional information: Type _IS3kShowLines can not be marshaled as an unmanaged structure; no meaningful size or offset can be computed.
I have removed unsafe I get the same error.
I have updated my post if you want to refere back to it.
Thanks
Uday Shastri
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