How to use function in other class c# -

i have app gui

i put function checkproxy() in form1.cs works correctly , want move function checkproxy() other class if put checkproxy() in other class error invoke , richtextbox3

namespace test3 { public partial class form1 : form {     public bool continuethreads = false;     string[] proxylist = null;     list<thread> threadlist = new list<thread>();     int proxynum = 0;     public form1()     {         initializecomponent();     }      private void button1_click(object sender, eventargs e)     {             int n = (int)numericupdown1.value;             thread[] tl = new thread[n + 1];             threadlist = tl.tolist();             (int = 0; <= n; i++)             {                 threadlist[i] = new thread(new threadstart(checkproxy));             }             (int = 0; <= n; i++)             {                 threadlist[i].start();             }             continuethreads = true;             proxylist = richtextbox1.lines;     }     public void checkproxy()     {         while (continuethreads)         {              if (proxynum >= proxylist.length)             {                 continuethreads = false;             }             if (proxynum < proxylist.length)             {                 string proxy = proxylist[proxynum];                 proxynum += 1;                 string info = "";                 try                 {                     thread.sleep(1000);                     info += "live || " + proxy + environment.newline;                     this.invoke(new action(() => richtextbox3.text += info));                 }                 catch                 {                  }             }         }     } } } 

this screenshot error

your method checkproxy uses form1 class members (continuethreads, proxynum , others) directly.

if want move outside of class (i'm not sure idea since method looks closely related class) - need refactor method , pass class members uses method input parameters

public void checkproxy(bool continuethreads.....)