|
I am trying to write a DLL that has an event and am subscribing to the event from 2 different programs, but each of my programs is creating a new instance of the DLL.
The class is a singleton class and looks like this:
public sealed class clsEvents
{
public static readonly clsEvents Instance = new clsEvents();
private string _Value = "";
public event EventHandler ValueChanged;
public void OnValueChanged(EventArgs e)
{
EventHandler handler = ValueChanged;
if (null != handler)
{
handler(this, e);
}
}
public string Value
{
get { return _Value; }
set
{
_Value = value;
OnValueChanged(EventArgs.Empty);
}
}
}The singleton class only does half the work so that the same instance of the class is shared within each program but I need to use the same instance in both programs. I have set both programs to compile into the same directory so I know they are loading the same DLL but they are each creating their own instance of the class.
Finally, my question:
In VB6 it is possible to set the Instancing of a DLL to Multiuse and any programs that use that DLL would share the same global variables from the DLL. Is it possible to do the same thing in C# so that each of my programs uses the same instance of the singleton class?
Forgive me if I am going about this all wrong but hopefully someone can help. Please tell me if there is a better way to share events across multiple programs.
|
|
|
|
|
I'm afraid I think you're out of luck with this. Each of your programs runs in its own process and the operating system ensures that processes are independant of one another. Your dll will be loaded twice - once into each process, and even though you have implemented a singleton you ultimately have two of them on your computer.
You need to look at inter-process communication, something like named pipes perhaps or you might be able to get away with Mutexs. Hopefully someone here might have done this before.
Regards,
Rob Philpott.
|
|
|
|
|
I'm not certain of my solution...I'm just trying to throw ideas your way. What about exposing this as a web service and having it influence a state machine on your server? Then, you could just proxy into the service in both apps and whenever you would trigger the event from inside each of the programs, it would actually fire the event in a single location. But again, I might be oversimplifying your specific problem.
|
|
|
|
|
...a web service is my preferred choice for allowing concurrent execution of a shared process. They're fairly straight forward and since replies from the server are sent as SOAP, they can be consumed by pretty much any language you want to work in.
|
|
|
|
|
How to reveal values of all public properties of an object, without referring to property names?
Thanks.
|
|
|
|
|
Looks like Civic has the same homework!
|
|
|
|
|
It does indeed.
the last thing I want to see is some pasty-faced geek with skin so pale that it's almost translucent trying to bump parts with a partner - John Simmons / outlaw programmer
Deja View - the feeling that you've seen this post before.
|
|
|
|
|
Thank you. The problem is solved.
|
|
|
|
|
I have an object and want to call a method which will automatically go through all its properties and display its values. How can i do that without manually specifying object.length for example.
|
|
|
|
|
|
|
Civic06 wrote: I have an object and want to call a method which will automatically go through all its properties and display its values.
Use reflection. Call GetType() to get the object's type (I presume that is also an unknown). From there you can GetProperties(). For each of the PropertyInfo objects you can now invoke the getter method. This will return the value of the property. It is then up to your application how to render that to the user.
|
|
|
|
|
I'm having an error message sounding like :
Prepared statement '(@id text)SELECT * from isp_email.staff where @id like +txtname.' expects parameter @id, which was not supplied.
This message appear when I press button to select a row at run time. What could be the problem?
SqlCommand myCommand = new SqlCommand();
myCommand.Connection=con;
myCommand.CommandText="SELECT * from isp_email.staff where @id like +txtname.Text";
SqlParameter myparam = new SqlParameter("@id",SqlDbType.Text);
myparam.Value=ID;
myCommand.Parameters.Add(myparam);
SqlDataAdapter myAdapter=new SqlDataAdapter(myCommand);
DataSet ds = new DataSet();
myAdapter.Fill(ds);
con.Open();
myCommand.ExecuteNonQuery();
dgupdate.DataSource=ds;
dgupdate.DataBind();
con.Close();
Thank you.
|
|
|
|
|
That error does not match what I see. However there is an error here:
nclauder wrote: myCommand.CommandText="SELECT * from isp_email.staff where @id like +txtname.Text";
The parameter @id is used in place of column name.
Also, txtname.Text will not be understood by SQL Server as it has no knowledge of your form. If you want to use the value from your textbox control then you really need to validate the value and/or sanitise its value and put send it as a parameter. Attempting to inject it will just open your application up to security holes.
|
|
|
|
|
You have code inside your SQL statement
"SELECT * from isp_email.staff where @id like" + txtname.Text;
fixes that...but not quite what you want
I would assume that '@id' is your parameter and you don't have a column in your table named '@id'. You need to look up the usage of parameterized queries. ...You don't place the parameter as substitution for the column name. Parameters are meant to hold values, not field names
|
|
|
|
|
Alaric_ wrote: "SELECT * from isp_email.staff where @id like" + txtname.Text;
Oh Yeah! Another person advising people to put great big security holes in their application. 
Please read about SQL Injection Attacks and how to prevent them.[^]
Alaric_ wrote: You need to look up the usage of parameterized queries.
You know about parameterised queries, but you don't advocate it for putting in the value from the TextBox.  If you know how to do parameterised queries, why inject the value from the TextBox? 
|
|
|
|
|
fixes that...but not quite what you want
...I guess you missed that line. I was advising on syntax. ....Baby steps.
-- modified at 16:50 Wednesday 10th January, 2007
Should be read: Just because I didn't provide information extraneous to the request doesn't mean that I don't know about it.:-> If he would have asked something along the lines of, 'Is this safe?' then I would have given him suggestions on scrubbing his data. ...Another thing, how do you know that his data wasn't scrubbed before the query was specified? I do character validation at the input level to disable invalid input and for any of the text fields that I know are going to be sent through to a query, I send through my SQL formatter. The document you suggested is good for raising discussion but by no means is it perfect. He'll learn about securing his database in his 300 level dba classes. To make the whole thing completely copacetic, I should have suggested something more along the lines of
"SELECT * from isp_email.staff where @id like" + db.ToSQL(txtname.Text);
...happy? (*Note* Remember that it's still not right because he misused the parameter)
|
|
|
|
|
How do I check what kind of file system is installed on a specific drive and is there a way to check if the drive is a CD, an Network share or an USB Drive.
My starting point is like:
---------------------------------
bool driveExist = false;<br />
string[] drives = System.IO.Directory.GetLogicalDrives();
---------------------------------
/Thomas
-- modified at 10:29 Wednesday 10th January, 2007
|
|
|
|
|
|
Hi,
I'm used to c++, and now, with c#, there's one thing that is annoying me:
I want to write text files to disk sequentially, so I dediced to use a StreamWriter. Well, first I create my StreamWriter
StreamWriter filewriter = new StreamWriter(DateTime.Now.ToString("yyyyMMddHHmmss"));
After using it, I close it
filewriter.Close();
and then, how can I open a new file with the same stream writer? Do I have to instance a new streamwriter again? I'm missing c++ filewriter.Open(DateTime.Now.ToString("yyyyMMddHHmmss"));
Thanks in advance.
|
|
|
|
|
The stream writer works as a wrapper around a specific stream. When you close the stream writer it's disposed and not usable any more. To write another stream you create a new stream writer for that stream.
---
Year happy = new Year(2007);
|
|
|
|
|
Ok, thank you for the information. So, now the question is: Is there a file stream oriented object more specialized in reusability?
|
|
|
|
|
jarellan wrote: Is there a file stream oriented object more specialized in reusability?
It has been several years since I last used C++, but I don't think you reused the file resources in C++ either. The when you re-opened a stream you would most likely get a different file handle internally anyway. It was just the class's public interface that made it appear otherwise.
Also, when you Dispose an object in C# (or close a stream) it tells the garbage collector to suppress the finaliser (the .NET equivalent of a destructor). The Finaliser is a safety mechanism in case the managed .NET object goes out of scope while holding onto unmanaged resources, like a file handle. Because the Dispose method and Close method cleans up the unmanaged resources the object can be flagged as not needing to run the finalizer any more. This speeds up garbage collection.
It is possible for an object to call ReRegisterForFinalizer if it needs to, but the documentation does list this very important caveat "Calling the ReRegisterForFinalize method does not guarantee that the garbage collector will call an object's finalizer." [my emphasis]. Without the gurarantee the application could leak memory all over the place if the developer of the client code forgot to call Dispose or Close, or was not disciplined into ensuring that it was called.
I hope this helps.
|
|
|
|
|
I thought c++ fstream open-close doesn't reallocate memory resources...
Anyway, everything I found on the Internet was about StreamWriter, so I think it's the best option...
Thankyou very much.
|
|
|
|
|
jarellan wrote: Is there a file stream oriented object more specialized in reusability?
No, there isn't.
Don't worry about creating a few objects, the memory management in .NET is built to handle that efficiently. Short lived objects are easily handled by the garbage collector, it's actually the objects that you hold on to a bit longer that gets more expensive.
As memory allocation is more expensive in C++, the classes are built for reusability. In .NET it's generally more efficient to just create a new object, so the classes are more often built to be used just once.
---
Year happy = new Year(2007);
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
