Winform 上的文本框不显示我的数据 C#

Question

I'm creating a Windows form where it should list the COM Ports on my PC. I'm trying to add this data to a ComBox, where it will list/display all my COM Ports and the details of each one. This is the code.

    private void cb1_SelectedIndexChanged(object sender, EventArgs e)
    {
        using (var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_PnPEntity WHERE Caption like '%(COM%'"))
        {
            var portnames = SerialPort.GetPortNames();
            var ports = searcher.Get().Cast<ManagementBaseObject>().ToList().Select(p => p["Caption"].ToString());

            var portList = portnames.Select(n => n + " - " + ports.FirstOrDefault(s => s.Contains(n))).ToList();

            foreach (string s in portList)
            {
                cb1.Text = s;
            }
        }
    }

This code works perfectly in a Console App, it shows exactly what I need. But in the Windows Form, it is not working. I have googled some possible solutions for this, but none of them worked. I am not an expert on that, but I believe this error could be something related with the Data Bindings, I tried to remove the Data Bindings but I couldn't.

cb1.DataSource = null; or cb1.Items.Clear();

These were just two of many things that I tried but none worked.

Answer 1

You are currently not adding any items to the ComboBox. Check out the modified code.

private void cb1_SelectedIndexChanged(object sender, EventArgs e)
{
    using (var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_PnPEntity WHERE Caption like '%(COM%'"))
    {
        var portnames = SerialPort.GetPortNames();
        var ports = searcher.Get().Cast<ManagementBaseObject>().ToList().Select(p => p["Caption"].ToString());

        var portList = portnames.Select(n => n + " - " + ports.FirstOrDefault(s => s.Contains(n))).ToList();

        foreach (string s in portList)
        {
            cb1.Items.Add(s); //THIS LINE CHANGED
        }
    }
}

You want to add the available COM Ports to the ComboBox so you have to add a new Item for every COM Port. This items can be selected by the user after they are inserted.

EDIT: To run the code when opening your form you should do something like this:

public Form1() {
  InitializeComponent();

  using(var searcher = new ManagementObjectSearcher("SELECT * FROM Win32_PnPEntity WHERE Caption like '%(COM%'")) {
    var portnames = SerialPort.GetPortNames();
    var ports = searcher.Get().Cast<ManagementBaseObject>().ToList().Select(p => p ["Caption"]
                                                                                     .ToString());

    var portList = portnames.Select(n => n + " - " + ports.FirstOrDefault(s => s.Contains(n))).ToList();

    foreach (string s in portList) {
      cb1.Items.Add(s);  // THIS LINE CHANGED
    }
  }
}