非阻塞io使用BinaryWriter寫入到usblp0

Question

我正在做一個程序在c＃（單聲道）打印到財務打印機（escpos），它工作正常。問題是，當我打印時，程序掛起，直到我有的緩衝區被清除。所以，如你所想象的，如果我打印一些圖像，它會變得更大，所以它會暫停一段時間。這是不可取的。

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.");    
} 

第二種方式：我已經在兩個方面

一種方式測試

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

既不方法允許程序繼續執行。例如：如果它開始打印並且紙張已用完，則它將掛起，直到打印機恢復打印，這是不正確的。

在此先感謝您的時間和耐心。

Answer 1

問題是您正在讓程序等待寫入完成。如果你想讓它異步發生，那麼你需要提供一個回調方法，當寫入完成時會被調用。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. 
} 

這是一種方法。您應該閱讀Asynchronous Programming Model以瞭解其他選項，並選擇最適合您需求的選項。您可以使用Task Parallel Library，這可能更適合。