how to solve error port is closed when calling a function

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HI....
I have 2 forms form1&form2. Form1 contains a serial port. This port is opened in form load.

C#

private void Form1_Load(object sender, EventArgs e)
          {
               serialPort1.Open();
          }

I want to write to serial port through form2. For that I created a function in form1 for writing to serial port.

C#

public void SerialPortValueUpdated()
       {
           byte[] head = new byte[1] { 0xAA };
           byte[] trail = new byte[1] { 0x55 };
           byte[] llen = new byte[1] { length };
           // head = Convert.ToByte(0xAA);
           //serialPort1.Open();
           serialPort1.Write(head, 0, 1);
           serialPort1.Write(llen, 0, 1);
           serialPort1.Write(trail, 0, 1);
       }

and called this function from form2 like this

C#

private void button1_Click(object sender, EventArgs e)
{
    Form1 F = new Form1();
    F.SerialPortValueUpdated();
   }

But when I calling this function I get an error that 'Port is closed'. How can I solve this.
Please help me.

Posted 10-Sep-14 21:12pm

Member 10994712

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George Jonsson 11-Sep-14 5:49am

Why do you have two questions at the same time for what seems to be the same application?
Closing form in serialport datareceived event[^]
Maybe join the two.

2 solutions

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George Jonsson · Answer 1 · 2014-09-10T21:19:00

Solution 1

Add a try-catch clause in your code.
You might have a hidden error in Form1_Load.

C#

private void Form1_Load(object sender, EventArgs e)
{
    try
    {
        serialPort1.Open();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
}

[Update]
You need to show the form to activate Form_Load.

C#

private void button1_Click(object sender, EventArgs e)
{
    Form1 F = new Form1();
    F.Show();   // Will show a modless dialog.
    F.SerialPortValueUpdated();
}

This is not the best way to start a form with in a form.
Look into using a background worker instead.
BackgroundWorker Class[^]
But it depends what you want to do.

[Update]
For logging and status of your serial communication, I recommend to use Portmon[^] from Sysinternals

Additional reading:
Simple Serial Communication with Microsoft Visual C# Express[^]
How To Work With C# Serial Port Communication[^]
Serial Port Communication In C#[^]

Posted 10-Sep-14 21:19pm

George Jonsson

Updated 10-Sep-14 23:40pm

v5

Comments

Member 10994712 11-Sep-14 3:26am

I added try catch. But now also I get the same error

George Jonsson 11-Sep-14 3:38am

See the updated answer.

Member 10994712 11-Sep-14 4:26am

I tried this. But 'Access to com35 is denied' message get.

George Jonsson 11-Sep-14 4:37am

That usually means that the port is already open by another application.
Can you open COM35 in a terminal program like HyperTerminal?

Member 10994712 11-Sep-14 4:46am

NO..I think the problem is that form1 is already opened. I write code form1 f=new form1();
f.show() in form2 load().But form1 is not closing.

George Jonsson 11-Sep-14 4:57am

Ok, ok. So you have opened the port yourself.
Do you create multiple instances of Form1?
Well, maybe it is time to consider your application design.

Member 10994712 11-Sep-14 5:13am

no..:-(

George Jonsson 11-Sep-14 5:28am

Seems like your initial problem is solved and now the next error occurs.
If you get access denied on a specific COM port, it usually means that it has been opened by either another application or inside your own code prior to your call.

Member 10994712 11-Sep-14 5:20am

I have no idea about how to solve this..

George Jonsson 11-Sep-14 5:42am

Have you tried
if ((serialPort1.IsOpen == true)) // place break point here
serialPort1.Close();
Just to see what happens?

Member 10994712 11-Sep-14 6:33am

I checked this condition.This condition is false. That means port is closed

George Jonsson 11-Sep-14 7:11am

So the port is not opened by the current instance of serialPort1.
So what happens if you use the HyperTerminal (or any other terminal) and try to open the port when your application is not running?
Have you tried PortMon?

Member 10994712 11-Sep-14 7:19am

unable to open port35

George Jonsson 11-Sep-14 7:32am

How do you expect your application to be able to open COM35, if HyperTerminal fails?
You must have some app running that hogs COM35.
What hardware is behind COM35? A FTDI USBToRS232 dongle or what do you have?

Member 10994712 11-Sep-14 7:40am

communication port is 35,USB-to-serial is 43.

George Jonsson 11-Sep-14 8:03am

Que?
Use your language skills and explain a bit better.

Member 10994712 12-Sep-14 1:18am

I found a solution for this problem.. But am not sure about it. I think using tab control will help me. Am testing that.

Member 10994712 15-Sep-14 23:57pm

How can I solve this.. Still I have this problem..

George Jonsson 16-Sep-14 0:40am

You show very little of your code and I am not sure I want to see more of it.
I think you need to start from scratch and consider what it is you want to achieve and how to get there. Use your favorite browser in order to find examples.
Divide your solution into smaller pieces and solve them one by one.
The multiple forms solution you have right now is obviously not working.

Richard MacCutchan · Answer 2 · 2014-09-10T21:20:00

Solution 2

In your button1_Click method you are creating a new Form1 object, and calling the serial port method on that new object. But since that object has not gone through form loading it will not contain an open serial port. You need to call the method on the original Form1 object created at the start of the program.

Posted 10-Sep-14 21:20pm

Richard MacCutchan

Comments

Member 10994712 11-Sep-14 3:32am

can you explain it detail?? I used the same object.

Richard MacCutchan 11-Sep-14 3:59am

No you didn't, you create a new object in that method so it will not contain an open serialport, as I explained. If you don't understand object lifetimes you need to go and read your study guides.