c# Network adapters list

I have code, which is using System.Net and System.Net.NetworkInformation references, it generates a list of my network connection names.

Everything seems fine and working, but when I made a class of this code, and exported values to listbox1 items add, I had only one network connection name, but really I have four.

How can I solve this problem?

private void button1_Click(object sender, EventArgs e)
{
    Adapters obj = new Adapters();
    var value = obj.net_adapters();
    listBox1.Items.Add(value);
}

public class Adapters
{
    public string net_adapters()
    {
        string value = string.Empty;
        foreach (NetworkInterface nic in NetworkInterface.GetAllNetworkInterfaces())
        {
            value = nic.Name;
        }
        return value;
    }
}