string s =inbox.Text;
            string[] sArray = s.Split(',');
            foreach (string i in sArray)
            {
                if (i.Trim() != "")  
                    Console.WriteLine(i) ;   //这里是屏幕打印的
                    this.outbox.Text=这里怎么写; 
           }

string s =inbox.Text;
string[] sArray = s.Split(',');

outbox.Multiline = true;
outbox.Text = string.Join("\n", sArray);

------解决方案--------------------
探讨

C# code
string s =inbox.Text;
string[] sArray = s.Split(',');

outbox.Multiline = true;
outbox.Text = string.Join("\n", sArray);


------解决方案--------------------
string.Join("\n", sArray);

------解决方案--------------------
更正:

outbox.Text = string.Join("\r\n", sArray);