How can I call Serial Port declare in Main Form from a class

When I ran your serial problem project the system null error message came up, but looking at the code -it should have worked. To check MainForm load event I click on the form in designer view and another MainForm load event appeared in code window. I copied "Fm1 = this;" to that event and bingo it worked. Very simple fix 

There seemed to be a problem with mainform load
It's now working on my machine

Moving to the main form is the opposite of what experienced professionals would do.

Thanks for everybody suggestion. If still can not work, i think i just move all the code from Class1 back to Main Form

PS. Scan before open the attach file. Thanks.

The exception you were getting originally (UnauthorizedAccessException was unhandled) was in fact nothing to do with serialPort1 being private (which would show up at compile time) but probably meant that the serialport had already been opened either from somewhere else in your own program or by a different program.


I am therefore puzzled why this exception has now gone away and you're getting a null reference exception on this line:


 MainForm.Fm1.serialPort1.Open(); //NullRefenceException was unhandled


On the face of it, it's simply not possible for either Fm1 to be null (given the nature of Frogleg's amendments) or for serialPort1 (assuming you've added it from the VS designer) to be null. Do you perhaps have another variable called MainForm in Class1 which is hiding the class of the same name?

Did you put this in main form
public partial class MainForm : Form

{
public static MainForm Fm1 = null; // creates single instance<<<<<<<<<

public MainForm()

{

InitializeComponent();

}


private void MainForm_Load(object sender, EventArgs e)
{
Fm1 = this;//<<<<<<<<<<<<<<<
}

Thanks Frogleg, the private problem had solve.
But, another problem,

MainForm.Fm1.serialPort1.Open(); //NullRefenceException was unhandle
MainForm.Fm1.serialPort1.Write(new byte[] { 0x55 }, 0, 1);  //NullRefenceException was unhandle

How to create new instance for this? Thanks

Try this



namespace WindowsFormsApplication1

{

public partial class MainForm : Form

{
public static MainForm Fm1 = null; // creates single instance

public MainForm()

{

InitializeComponent();

}


private void MainForm_Load(object sender, EventArgs e)
{
Fm1 = this;
}


private void button1_Click(object sender, EventArgs e)

{

try

{

serialPort1.PortName = "COM1";

serialPort1.BaudRate = 9600;

serialPort1.DataBits = 8;

serialPort1.Parity = Parity.None;

serialPort1.StopBits = StopBits.One;

serialPort1.Open();

disconnectBtn.Enabled = true;

connectBtn.Enabled = false;

}



catch

{

MessageBox.Show("Error", "Unable To Access", MessageBoxButtons.OK, MessageBoxIcon.Error);

}



if (connectBtn.Enabled == false)

{

textBox1.Text = "Connected";

}

}



private void disconnectBtn_Click(object sender, EventArgs e)

{

try

{

serialPort1.Close();

connectBtn.Enabled = true;

disconnectBtn.Enabled = false;

}

catch

{

MessageBox.Show("Error", "Unable To Access", MessageBoxButtons.OK, MessageBoxIcon.Error);

}

if (disconnectBtn.Enabled == false)

{

textBox1.Text = "Disconnected";

}

}



private void button1_Click_1(object sender, EventArgs e)

{

serialPort1.Write(new byte[] {0x55}, 0, 1); //OK

}



private void button2_Click(object sender, EventArgs e)

{

Class1 sp = new Class1();

sp.serialOut();

}

}

}

[/code]

But, when i click button2 link to class2 to call serial port, it does not work.
[code]

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO.Ports;



namespace WindowsFormsApplication1

{

class Class1

{

public void serialOut()

{


MainForm.Fm1.serialPort1.Open(); //UnauthorizedAccessException was unhandle

MainForm.Fm1.serialPort1.Write(new byte[] { 0x55 }, 0, 1); //InvalidOperationException was unhandle

}

}

}

This code works with serial port set to public, but with a bit more code you can set it back to private