目录
第1章说明
1 为什么需要异步写数据?
如下图所示,以波特率300打开一个串口。
图1
单击"同步发送"按钮,则数据未发送完之前写数据的函数不会返回。波特率300,每秒大概能发送25个字符,发送500个字符就需要20秒。这20秒之内,整个程序将处于假死状态。
单击"异步发送"按钮,就不会出现假死状态。
2 异步写数据的代码
异步写数据的代码如下:
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); } } |
要点为:
1)GetCommHandle函数获取.NET SerialPort对象的串口句柄hComm;
2)调用WriteFile函数,异步写数据。
以下是结构OVERLAPPED的声明、函数WriteFile的声明、函数GetCommHandle的实现:
[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; } |
3 源代码
本文的代码已上传至git服务器:
https://github.com/hanford77/Exercise
https://git.oschina.net/hanford/Exercise
在目录 SerialPort\c# 目录内。