Hi all,

i have a Class that handles Barcode scanning functionality, and a Windows Form that contains an instance of this Barcode class. One of the Properties of the Barcode Class is an Event, which is triggered when the user executes a successful barcode scan. What I want is to be able to somehow call a method belonging to the Form from within the handled event that sits in Barcode class. How can I do this? The extremely watered down code is below...

// Barcode Class
class clsBarcodeScanner
{
// Declare and initialise EventsHandlers.
private System.EventHandler MyEventHandler = null;

private bool InitReader()
{
// Create event handler delegate
this.MyEventHandler = new EventHandler(MyReader_ReadNotify);
}

private void MyReader_ReadNotify(object sender, EventArgs e)
{
// If it is a successful read (as opposed to a failed one)
if (MyReaderData.Result == Symbol.Results.SUCCESS)
{
// WHAT TO CALL THE FORM METHOD HERE!
}
}
}

// Form Class
public class FormSnagList : System.Windows.Forms.Form
{
private clsBarcodeScanner m_clsBarcodeScanner;

public FormSnagList()
{
m_clsBarcodeScanner = new clsBarcodeScanner();
}

public void MethodWantToCall()
{
// THE METHOD I WANT TO CALL.
}
}

Hope you can help.

Thanks

Tryst

Tryst,glad to be of help!!

Can you kindly mark this as an answer?

Hi,
see if this works for you:

// Barcode Class
class clsBarcodeScanner
{
// Declare and initialise EventsHandlers.
private System.EventHandler MyEventHandler = null;
// Declare a reference to the form
private FormSnagList MyForm = null;

public clsBarcodeScanner(FormSnagList form)
{
MyForm = form;
}

private bool InitReader()
{
// Create event handler delegate
this.MyEventHandler = new EventHandler(MyReader_ReadNotify);
}

private void MyReader_ReadNotify(object sender, EventArgs e)
{
// If it is a successful read (as opposed to a failed one)
if (MyReaderData.Result == Symbol.Results.SUCCESS)
{
if(MyForm != null)
MyForm.MethodWantToCall();
}
}
}

// Form Class
public class FormSnagList : System.Windows.Forms.Form
{
private clsBarcodeScanner m_clsBarcodeScanner;

public FormSnagList()
{
m_clsBarcodeScanner = new clsBarcodeScanner(this);
}

public void MethodWantToCall()
{
// THE METHOD I WANT TO CALL.
}
}

I added an attribute to the clsBarcodeScanner that will hold a reference to the form. This way you may call the method you want.

Hi Tryst,I think it may be a good idea to implement the Observer pattern here,since your clsBarCodeScanner should not need to know as to which method to call on the FormSnagList form.The approach should be that FormSnagList (or anybody else)should register its interest with the clsBarCodeScanner and whenever the state of clsBarCodeScanner changes,it will notify all objects who have interest.

Here is the code-

//Any object which wants other object to register its interest with itself will implement this interface

interface IObservable

{

void AddObserver(IObserver observer);

void Notify();

}

//Any object which wants to update itself when notified by the subject will implement this interface

interface IObserver

{

void Update();

}

class clsBarcodeScanner : IObservable //Allows objects to register itself

{

// Declare and initialise EventsHandlers.

private System.EventHandler MyEventHandler = null;

private ArrayList list = new ArrayList();

public void AddObserver(IObserver observer) //Add observers

{

list.Add(observer);

}

private bool InitReader()

{

// Create event handler delegate

this.MyEventHandler = new EventHandler(MyReader_ReadNotify);

return true;

}

private void MyReader_ReadNotify(object sender, EventArgs e)

{

// If it is a successful read (as opposed to a failed one)

if (MyReaderData.Result == Symbol.Results.SUCCESS)

{

Notify(); //Notify all observers

// WHAT TO CALL THE FORM METHOD HERE!

}

}

#region IObservable Members

public void Notify()

{

foreach (IObserver observer in list)

observer.Update(); //Loop through each observer asking it to update itself

}

// Form Class

public class FormSnagList : System.Windows.Forms.Form, IObserver

{

private clsBarcodeScanner m_clsBarcodeScanner;

public FormSnagList()

{

m_clsBarcodeScanner = new clsBarcodeScanner();

m_clsBarcodeScanner.AddObserver(this); //Add self to the clsBarCodeScanner

}

public void MethodWantToCall()

{

// THE METHOD I WANT TO CALL.

}

#region IObserver Members

void IObserver.Update()

{

MethodWantToCall(); //Call method when notified

}

#endregion

}

This achieves high level of decoupling and importantly,the observer itself can serve as an observable later.

Thanks for the reply people!

Karthik Krishnaswami, that is a fantastic example! It works a treat!

I never knew this pattern existed!

Thanks

Tryst

this should work i think

public delegate void FormNotifyEventhandler();

// Barcode Class
class clsBarcodeScanner
{
// Declare and initialise EventsHandlers.
private System.EventHandler MyEventHandler = null;

public event FormNotifyEventhandlernotify;

private bool InitReader()
{
// Create event handler delegate
this.MyEventHandler = new EventHandler(MyReader_ReadNotify);
}

private void MyReader_ReadNotify(object sender, EventArgs e)
{
// If it is a successful read (as opposed to a failed one)
if (MyReaderData.Result == Symbol.Results.SUCCESS)
{
Notify

}
}
}

// Form Class
public class FormSnagList : System.Windows.Forms.Form
{
private clsBarcodeScanner m_clsBarcodeScanner;

public FormSnagList()
{
m_clsBarcodeScanner = new clsBarcodeScanner();

m_clsBarcodeScanner.notify += new System.EventHandler(this.MethodWantToCall);

}

public void MethodWantToCall()
{
// THE METHOD I WANT TO CALL.
}
}

Remco

Tryst,glad to be of help!!

Can you kindly mark this as an answer?