Serial Port Data access in all windows forms

Your static class will look someting like this

public class SerialPortClass
 {
     private static SerialPortClass instance;

     public static SerialPortClass GetInstance()
     {
         return instance ?? new SerialPortClass();
     }

     SerialPort port;
     //Rest of your serial port class members and methods here....

     public void SendData(byte[] data)
     {
         port.Write(data,0,data.Count());
     }

     protected void Connect()
     {
         port = new SerialPort("COM1");
         //portsettings
         //port.BaudRate = 1024;
     }
 }

Your implementation or calls inside the other forms will look like

SerialPortClass.GetInstance().Write(data);

The obvious issue with having multiple forms accessing a any sort of serial class or even device is working out how to deal with who is handling the data.

I mean the serial object whatever it looks like holds data does the first form to ask for it get it or are the forms expected to callback and say ok next data I have handled that one. Then you have the issue of partial data somehow the serial stream must have data blocks of some form with end of data markers and the forms are obviously needing to parse that data with a complete block not a half block.

That leads me to the obvious conclusion none of the ideas above will really work well.

It would appear to me you are trying to make a message queue which for all purposes looks very much like a standard windows queue and that would give you a good clue to do this in a very elegant way.

1.) Design your own message queue system
2.) Attach your own private message into the standard windows handler

Personally I would go for option 2 the windows message handler is well behaved and you know how it will behave so all you do is make your own private WM command and say for example attach the parsed data to the LPARAM. Microsoft makes this easy they expect you to do it.

WM_MYPRIVATEMSG (WM_USER + 0x0001) 

You use standard windows PostMessage and SendMessage commands to post them up to a specific form or system wide if you want simply based on window handle. You can even Register the message using RegisterWindowMessage if you really want and make the serial object as it's own thread or application.

The point is it stays with one serial object playing around with the serial port and the forms just handle a new WM_MYPRIVATEMSG which will be posted out in usual way.

Hell you could get really fancy and send message back to the serial object by using the same technique if you need to control it.

What all that does it makes the whole the structure portable and consistent and will be supportable over time because there are many many applications that work that way and it is the recommended way to do it.

if i were you i would write windows Service for handling serial port and then use some key points for communication between windows form and windows service application.
but for your case it`s better to write up your code then guys can help you.

I made SerialPort reader into a separate static class. Then I created a datareceive event in that class and fire it every time data is received. And that event I subscribe in each form and now when I scan the card datarecived event is firing in every form.