.NET (Core and Framework)

Accessing functions or subs from another class.

7-Apr-12 22:06

Dim GlobalCollection as New Collection
Dim ChildCollection1 as New Collection
Dim tempCurrentCollection as Collection

That should give you intellisense on the temp object Smile | :)

Bastard Programmer from Hell Suspicious | :suss:

Member 85988664-Apr-12 5:03

Member 8598866

4-Apr-12 5:03

I am new to the vb.net language and there seems a few ways to accomplish accessing items from another class.

My question, what would be best or proper method or why would use 1 method over the other..
Again I am generally new at this and would greatly appreciate knowing what is preferred and why would you use 1 method over the other.

Shared items.

Class1
Public shared sub1
end sub
end class

Then in class2 use class1.sub1.

----------------------
or use an instance.

Class1
Public sub1
end sub
end class

then in class2 use
Dim Myclass1 as new class1
( or should it be Dim Myclass1 as class1 = new class1)
then use myclass1.sub1....

------------------------------
or use inherits

Class1
Public sub1....
end sub
end class

then in class2 use
inherits class1
then use sub1.....

Thanks for any info
Steven

Re: Accessing functions or subs from another class.

Eddy Vluggen4-Apr-12 5:21

Asynchronous webservice calls and threading

4-Apr-12 5:21

You group methods together in a class. If those objects take similar parameters, then it's kind of convenient to make an "object" of it, storing the parameters right next to the methods that are going to interact with them. Compare this;

Structure SomeStruct
  Public Bla As String
End Structure
Class MyClass
  Shared Sub DoSomething(ByVal someBla as SomeStruct, Byval No as Integer)
    ' ..
  End Sub
  Shared Sub DoSomethingElse(ByVal someBla as SomeStruct, Byval s as String)
    ' ..
  End Sub
End Class

'example usage;
Dim x as SomeStruct
MyClass.DoSomething(x, 1)
MyClass.DoSomethingElse(x, "Hello")

To this;

Class MyClass
  Private _someBla as someStruct
  Sub New(someBla as someStruct)
    _someBla = someBla
  End Sub
  Sub DoSomething(Byval No as Integer)
    ' ..
  End Sub
  Sub DoSomethingElse(Byval s as String)
    ' ..
  End Sub
End Class

'example usage;
Dim x as SomeStruct
Dim newClass as new MyClass(x)
newClass.DoSomething(1)
newClass.DoSomethingElse("World")

You use "shared" if you don't interact with any properties of the object.

Bastard Programmer from Hell Suspicious | :suss:

CDP18024-Apr-12 0:19

CDP1802

4-Apr-12 0:19

I have a client program that uses a webservice for communication with its server. Up to now all calls to the webservice have been synchronous, but now they must be made asynchronously. The webservice has been wrapped into classes that handle and log communication errors and perform all conversions between entities and the structs used by the webservice. This way the client is practically unaware of the existence of the webservice and might as well be sitting on top of the application logic on the server. This compatibility will be lost when using asynchronous calls (the real application logic does not provide any methods and callbacks for asynchronous calls), but that is not really important. It would only have been useful in some testing scenarios where we might have wanted to take the webservice out of the picture.

Inside the wrapper classes, an asynchronous call will look something like this:

public void GetSomeEntityBySomeParameter(int SomeParameter)
{
    try
    {
        // the Webservice object is auto-generated from the WSDL of the service and an instance
        // has been created in the constructor, as well as hooking up the event handler method to
        // receive the results
        this.Webservice.GetSomeEntityBySomeParameterAsync(SomeParameter);
    }
    
    catch(Exception e)
    {
        // error while sending the request
        // here comes code to do some logging and
        // handling if possible
    }
}

private void Webservice_GetSomeEntityBySomeParameterCompleted(object sender, SomeEventArgs e)
{
    SomeEntity Result = null;
    

    try
    {
        if(e.Result.ErrorReport != null)
        {
            // somme error has occurred on the server.
            // let's use the error info in the result to do some logging
            // and prepare some error info for the client
        }
        else
        {
            // let's convert the struct to an entity
            Result = ConvertSomeStructToEntity(e.Result.Value);
        }

        // *************** Big Mistake! ***************
        // this raises an event to notify the caller that the 
        // asynchronous call has been completed
        OnGetSomeEntityBySomeParameterFinished(Result);
    }
    
    catch(Exception e)
    {
        // something unexpected happened
        // little options to handle this, but let's
        // at least log all we can to provide some
        // info for debugging
    }
}

This last step, notifying the object that requested the data, is the part that gives me trouble. A separate thread has been started for the asynchronous call and also the Webservice_GetSomeEntityBySomeParameterCompleted() method will be called from that thread. Once I'm done and raise my own event, the event handler of the caller will also be executed by that thread.

That's wrong in many ways. Usually the calls will be initiated from some object around the UI. The UIs from Microsoft simply throw an exception when changes to the UI are made by another thread. In this case the UI is not from Microsoft and reacts very well to multithreading, but there still are side effects. Also, it is simply unacceptable to lose control over which part of the code is executed by any given thread.

In the end I need some safe way to raise the GetSomeEntityBySomeParameterFinished event, so that its event handler is executed by the same thread that requested the data. I'm very careful here because pulling a thread away from what it is currently doing and making it do something else instead (if that's possible at all) is just asking for even more trouble

Edit: Added some typical exception handling, just for the sake of completeness

Edit^2: I have been looking at the System.Windows.Threading.Dispatcher class, which seems to do what I want to have. Unfortunately, as the namespace tells, that's WPF and I can't afford to include WPF just to get to use this class. Also, things like Control.Invoke would not help, even if the UI had such methods. My problems seem to come from a race condition in the presenters, which are not UI classes.

I'm invincible, I can't be vinced

modified 4-Apr-12 9:39am.

Eddy Vluggen4-Apr-12 5:10

4-Apr-12 5:10

CDP1802 wrote:
In the end I need some safe way to raise the GetSomeEntityBySomeParameterFinished event, so that its event handler is executed by the same thread that requested the data. I'm very careful here because pulling a thread away from what it is currently doing and making it do something else instead (if that's possible at all) is just asking for even more trouble

Everything is possible; a thread is usually a loop with work, until work is done and the thread exits. You could have a check inside that loop that checks for certain conditions or events and have it act.

There's various ways to have the thread check for conditions (like a thread-safe flag), but you might want to AutoResetEvent[^] class.

Bastard Programmer from Hell Suspicious | :suss:

CDP18024-Apr-12 5:58

CDP1802

4-Apr-12 5:58

As it seems, the System.Windows.Threading.Dispatcher class was designed just for such a case. It allows to raise an event that then is handled on the thread that the Dispatcher was created for. MSDN did not provide too many details, but it appears that pending events are put into a queue and the thread checks the queue and calls the event handlers. There we basically have the thread's loop that does the checking, hidden away in the framework so that the application does not need to take care of any details.

The problem is that this class is in a WPF namespace. It would work, but then I would lose the option to target other framework versions and platforms where the WPF namespaces don't exist. Two candidates would have been WinPhone 7 and the XBox. But why did they put this class into the WPF namespaces? It would be really helpful in many other cases, not just when some UI is involved.

And I still think that the complete loss of control over which thread gets to execute a callback for an asynchronous operation is very problematic. It's a real complication to make all classes that need to call to the webservice thread safe.

I'm invincible, I can't be vinced

Eddy Vluggen4-Apr-12 10:53

4-Apr-12 10:53

CDP1802 wrote:
The problem is that this class is in a WPF namespace. It would work, but then I would lose the option to target other framework versions and platforms where the WPF namespaces don't exist.

Do you have Reflector or ILSpy installed? If yes, then it's always worthwhile to see if you can reimplement it in a separate assembly (meaning, if it's a simple thing without too much references)

Bastard Programmer from Hell Suspicious | :suss:

NumberGroupSeparator not working?

cpkilekofp23-Apr-12 10:43

cpkilekofp

23-Apr-12 10:43

Have you investigated the BackgroundWorker class?

BackgroundWorker Class[^]

"It's not what you don't know that will hurt you the most, it's what you think you know that isn't so." - Unknown

Bernhard Hiller1-Apr-12 22:46

Bernhard Hiller

1-Apr-12 22:46

I tried to format a double using ToString("f2", System.Globalization.NumberFormatInfo.CurrentInfo). The NumberGroupSeparator is a single space, the NumberDecimalSeparator is a comma.
Hence I'd expect 3501.30 to be formatted as 3 501,30, but I get 3501,30 (i.e. the space after thousands is missing).
It is in a C# WPF application (value is not bound to a control, but to be writte to a text file) with .NET 4 on a Win 7 64 bit (German) OS.
Is that a bug in the framework, or must I use some tricks?

Eddy Vluggen1-Apr-12 23:37

1-Apr-12 23:37

Bernhard Hiller wrote:
Is that a bug in the framework

"SELECT" isn't broken.

You're formatting it as a fixed point number. Try the one below;

static void Main(string[] args)
{
    Console.WriteLine(
        3501.23.ToString("N2", System.Globalization.NumberFormatInfo.CurrentInfo));
    Console.ReadKey();
}

Bastard Programmer from Hell Suspicious | :suss:

Bernhard Hiller2-Apr-12 0:56

Bernhard Hiller

2-Apr-12 0:56

Thanks! What a difference...

Eddy Vluggen2-Apr-12 1:05

2-Apr-12 1:05

You're welcome Smile | :)