Two List Boxes in C# winform.

Karan please once follow below process:

Step-(01.) From where you calling your form there take a List.

public List ListBoxItems { get; set; }

ListBoxItems = new List( );

Step-(02.) Before open form check that LIST count. If LIST count > 0 then through loop add items from LIST to listbox.

Form1 frm = new Form1();

if(ListBoxItems.Count > 0)

{

// Add item to your listbox2

}

Step-(03.) On your Form1 when you are adding items to listbox2 from listbox1 then also add items to LIST - ListBoxItems

If this is helpful for you then please accept my Answer.