Question

我正在用c＃（单声道）打印一个程序来打印到财务打印机（escpos），它运行正常。问题是，当我打印时，程序会挂起，直到清除了我的缓冲区。所以，正如你想象的那样，如果我打印几张图像，它会变大，所以它会挂起一段时间。这是不可取的。我已经用2种方式进行了测试

单程：

BinaryWriter outBuffer;
this.outBuffer = new BinaryWriter(new  FileStream (this.portName,System.IO.FileMode.Open));
.... apend bytes to buffer...
IAsyncResult asyncResult = null; 
asyncResult = outBuffer.BaseStream.BeginWrite(buffer,offset,count,null,null);
asyncResult.AsyncWaitHandle.WaitOne(100);
outBuffer.BaseStream.EndWrite(asyncResult); // Last step to the 'write'.
if (!asyncResult.IsCompleted) // Make sure the write really completed.
{
throw new IOException("Writte to printer failed.");             
}

第二种方式：

BinaryWriter outBuffer;
this.outBuffer = new BinaryWriter(new  FileStream (this.portName,System.IO.FileMode.Open));
.... apend bytes to buffer...
outBuffer.Write(buffer, 0, buffer.Length);

并且两种方法都不允许程序继续执行。示例：如果它开始打印并且纸张已用完，它将一直挂起，直到打印机恢复打印，这不是正确的方法。

提前感谢您的时间和耐心。

Answer 1

问题是你正在让程序等待写完成。如果您希望它以异步方式发生，那么您需要提供一个在写入完成时将调用的回调方法。例如：

asyncResult = outBuffer.BaseStream.BeginWrite(buffer,offset,count,WriteCallback,outBuffer);

private void WriteCallback(IAsyncResult ar)
{
    var buff = (BinaryWriter)ar.AsyncState;
    // following will throw an exception if there was an error
    var bytesWritten = buff.BaseStream.EndWrite(ar);

    // do whatever you need to do to notify the program that the write completed.
}

这是一种方法。您应该阅读Asynchronous Programming Model了解其他选项，并选择最适合您需求的选项。

您也可以使用Task Parallel Library，这可能更合适。

非阻塞io使用BinaryWriter写入usblp0

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