C#中串口通信多个窗体操作一个控件

有2个窗体，Form1用来发送串口数据，Form2用来接收串口数据，但是接收不不到。。这是Form2的程序。
private void Form3_Load(object sender, EventArgs e)
{
sp.Open();

sp.ReceivedBytesThreshold = 1;
MessageBox.Show("ss");
sp.DataReceived +=new SerialDataReceivedEventHandler(sp_DataReceived);
MessageBox.Show("jieshouwan");
sp.Close();

}
public void sp_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
MessageBox.Show("kaishishou");
CheckForIllegalCrossThreadCalls = false;
List<byte> bytes = new List<byte>();
int n = sp.BytesToRead;
byte[] buffer=new byte[n];
sp.Read(buffer, 0, n);
// string data=null;
for (int i = 0; i < n; i++)
{
recdata += buffer[i].ToString();
}
MessageBox.Show(recdata);

}