I am following an online tutorial to learn how to write a serial communicator.
I am using VS2019 and .Net 5.0, which is different from the environment used in the tutorial.
To use the SerialPort tool, I try to create :
static SerialPort serialPort1;
as in the code:
using System;
using System.Windows.Forms;
using System.IO.Ports;
namespace SerialPortCommunication {
public partial class Form1 : Form {
static SerialPort serialPort1;
public Form1() {
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e) {
string[] ports = System.IO.Ports.SerialPort.GetPortNames();
comboBox1.Items.AddRange(ports);
comboBox1.SelectedIndex = comboBox1.Items.Count > 0 ? 0 : -1;
}
private void button1_Click(object sender, EventArgs e) {
if (button1.Text == "Open Port") {
serialPort1.PortName = comboBox1.Text;
serialPort1.Open();
button1.Text = "Close Port";
}
else {
serialPort1.Close();
button1.Text = "Open Port";
}
}
}
}
When I executed it , I encountered the System.NullReferenceException: ‘Object reference not set to an instance of an object.’
But after I changed it to
static SerialPort serialPort1 = new SerialPort();
the VS doesn’t show the Exception anymore.
My quesition is :
I have been told that we don’t need and we can not create an instance for a static object, but in this case why do I need to create one instance to initialize the serialPort1?
I am confused…
As a beginner, I may have some unclear concepts. Could you provide me with some guidance or recommend some resources for me to study?
>Solution :
That’s correct: you can’t create instances of static classes.
For example:
public static class Bob
{
public void Test() => Console.WriteLine("hello");
}
var bob = new Bob(); // this won't compile
Bob.Test(); // this will because you're calling a static method
SerialPort is not a static class:
public class SerialPort : System.ComponentModel.Component
What you have is a static field:
static SerialPort serialPort1;
And you’re assigning an instance of SerialPort to it:
serialPort1 = new SerialPort();
The only difference is that you’re doing this at the same time as declaring the field:
static SerialPort serialPort1 = new SerialPort();
In short: you’re not creating an instance of a static class, you’re instantiating a static field with an instance of the non-static class SerialPort.
P.S. Please also note the difference between fields and properties if you’re unaware of these concepts.