说明：  我需要用两个串口，连接两个仪器，现在我的程序是列出了两个选项框，分别让用户去选择，然后分别点击打开。串口号这么多，用户很多时候也不知道这两个分别连接的是哪个串口，所以很不方便。有什么办法可以让下拉框里只显示出相应的串口
(I need to use two serial port, connecting the two instruments, and now my program is listed two options box, let the user to select, and then click open. Serial number so much, users often do not know which two are connected to the serial port, so it is not convenient. Is there any way to allow the drop-down box to show only the corresponding serial port)