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

Question

I can call serial port in main from by clicking the button 1.

[code]

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;
namespace WindowsFormsApplication1
{
public partial class MainForm : Form
{
public MainForm()
{
InitializeComponent();
}
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 _mainForm = new MainForm();
_mainForm.serialPort1.Open(); //UnauthorizedAccessException was unhandle
_mainForm.serialPort1.Write(new byte[] { 0x55 }, 0, 1); //InvalidOperationException was unhandle
}
}
}

[/code]

I had set the serialPort1 to public in properties.

How can i solve this? Thank you.

Frogleg · Answer

A reusable class where the serial port is created inside the class

hello leong · Answer

Really learn something from you Frogleg. Thank you very much :)

Frogleg · Answer

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

hello leong · Answer

Thanks a lot Frogleg! Both version works on my computer too. May i know how you do it for the first version. This is my very first time using C# for my final year project. Thank you very much for your help :)

Frogleg · Answer

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

Sam Hobbs · Answer

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

hello leong · Answer

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.

Sam Hobbs · Answer

You should not need to make the form static. The serial port object should not be in the form. I think your problems are the result of using the form to contain something that should not be in the form.

Vulpes · Answer

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?

Frogleg · Answer

Can you upload your project

hello leong · Answer

Yes i did add those. But still prompt out exception error when i click the button. Thanks.

Suthish Nair · Answer

If the query got resolved then mark the post that helped you as Answer so will be helpful for others. Otherwise if you got the solution please share with us.

Frogleg · Answer

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;// }

hello leong · Answer

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

Frogleg · Answer

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