private void btnWriteAsync_Click(object sender, EventArgs e)

{//异步写

byte[] byt = System.Text.Encoding.Default.GetBytes(txtSend.Text);

if(byt!=null && byt.Length > 0)

{

IntPtr hComm = GetCommHandle(m_sp);

UInt32 w = 0;

m_ov.hEvent = IntPtr.Zero;

m_ov.Internal = IntPtr.Zero;

m_ov.InternalHigh = IntPtr.Zero;

m_ov.Offset = 0;

m_ov.OffsetHigh = 0;

WriteFile(hComm, byt, (UInt32)byt.Length, ref w, ref m_ov);

}

}

[StructLayout(LayoutKind.Sequential,Pack=4)]

public struct OVERLAPPED

{

public IntPtr Internal;

public IntPtr InternalHigh;

public UInt32 Offset;

public UInt32 OffsetHigh;

public IntPtr hEvent;

}

[DllImport("kernel32.dll", SetLastError = true

, CallingConvention = CallingConvention.Winapi)]

private static extern UInt32 WriteFile(IntPtr hFile, byte[] lpBuffer

, UInt32 nNumberOfBytesToWrite

, ref UInt32 lpNumberOfBytesWritten

, ref OVERLAPPED lpOverlapped);

protected System.IO.Ports.SerialPort m_sp =

new System.IO.Ports.SerialPort();

protected OVERLAPPED m_ov;

static IntPtr GetCommHandle(System.IO.Ports.SerialPort sp)

{//获得串口句柄，供 Win32 API 使用

IntPtr hComm = IntPtr.Zero;

if (sp != null)

{

object stream = typeof(System.IO.Ports.SerialPort).GetField("internalSerialStream", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance).GetValue(sp);

var handle = (Microsoft.Win32.SafeHandles.SafeFileHandle)stream.GetType().GetField("_handle", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance).GetValue(stream);

hComm = handle.DangerousGetHandle();

}

return hComm;

}