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       在邊寫這系列文邊和朋友們討論的過程中，璉大跟我提了一個想法『不要使用 DataReceived 事件，而自行用執行緒來檢查緩衝區』，這其實很類似在Socket 程式中利用Thread加上同步接收的方法，這篇就來討論如何來完成這樣的功能。

 

       做法其實滿簡單的，只是產生一個執行緒在其中執行一個迴圈 (DoReceive 方法)，在迴圈內檢查接收緩衝區是否有資料，如果有就執行 Read 方法接收，沒有資料則跳過。

Imports System.IO.Ports
Imports System.Threading
Public Class Form1
	Private receiving As Boolean
	Private comport As SerialPort
	Private totalLength As Int32 = 0
	Private t As Thread
	Private Delegate Sub Display(ByVal buffer As Byte())

	Private Sub DisplayText(ByVal buffer As Byte())
		TextBox1.Text &= String.Format("{0}{1}", BitConverter.ToString(buffer), Environment.NewLine)
		totalLength = totalLength + buffer.Length
		Label2.Text = totalLength.ToString()
	End Sub
	Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
		comport = New SerialPort("COM5", 9600, Parity.None, 8, StopBits.One)
		If comport.IsOpen = False Then
			comport.Open()
			receiving = True
			t = New Thread(AddressOf DoReceive)
			t.IsBackground = True
			t.Start()
		End If
		
	End Sub

	Private Sub DoReceive()
		Dim buffer(1023) As Byte
		While receiving = True
			If comport.BytesToRead > 0 Then
				Dim length As Int32 = comport.Read(buffer, 0, buffer.Length)
				Array.Resize(buffer, length)
				Dim d As New Display(AddressOf DisplayText)
				Me.Invoke(d, New Object() {buffer})
				Array.Resize(buffer, 1024)
			End If
			Thread.Sleep(16)
		End While
	End Sub

	Private Sub Button_ClearTextbox_Click(sender As System.Object, e As System.EventArgs) Handles Button_ClearTextbox.Click
		TextBox1.Clear()
	End Sub

	Private Sub Button_AbortThread_Click(sender As System.Object, e As System.EventArgs) Handles Button_AbortThread.Click
		receiving = False
	End Sub
End Class

 

 

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO.Ports;
using System.Threading;
namespace ThreadReceiveCS
{
	public partial class Form1 : Form
	{
		public Form1()
		{
			InitializeComponent();
		}
		private Boolean receiving;
		private SerialPort comport;
		private Int32 totalLength = 0;
		private Thread t;
		delegate void Display(Byte[] buffer);

		private void DisplayText(Byte[] buffer)
		{
			TextBox1.Text += String.Format("{0}{1}", BitConverter.ToString(buffer), Environment.NewLine);
			totalLength = totalLength + buffer.Length;
			Label2.Text = totalLength.ToString();
		}

		private void Form1_Load(object sender, EventArgs e)
		{
			comport = new SerialPort("COM5", 9600, Parity.None, 8, StopBits.One);
			if (!comport.IsOpen)
			{
				comport.Open();
				receiving = true;
				t = new Thread(DoReceive);
				t.IsBackground = true;
				t.Start();
			}
		}

		private void DoReceive()
		{
			Byte[] buffer = new Byte[1024];
			while (receiving)
			{
				if (comport.BytesToRead > 0)
				{
					Int32 length = comport.Read(buffer, 0, buffer.Length);
					Array.Resize(ref buffer, length);
					Display d = new Display(DisplayText);
					this.Invoke(d, new Object[] { buffer });
					Array.Resize(ref buffer, 1024);
				}
				Thread.Sleep(16);
			}
		}

		private void Button_ClearTextbox_Click(object sender, EventArgs e)
		{
			TextBox1.Clear();
		}

		private void Button_AbortThread_Click(object sender, EventArgs e)
		{
			receiving = false;
		}
	}
}

 

       在類別內宣告的部份，有一個型別為Boolean的receiving變數，這個變數的功能是為了能讓DoReceive方法內的While迴圈停止；另外有一個Thread型別的變數t，則是為了產生執行緒所宣告。接著來瞭解一下DoReceive方法。

 

 

	Private Sub DoReceive()
		Dim buffer(1023) As Byte
		While receiving = True
			If comport.BytesToRead > 0 Then
				Dim length As Int32 = comport.Read(buffer, 0, buffer.Length)
				Array.Resize(buffer, length)
				Dim d As New Display(AddressOf DisplayText)
				Me.Invoke(d, New Object() {buffer})
				Array.Resize(buffer, 1024)
			End If
			Thread.Sleep(16)
		End While
	End Sub

 

 

		private void DoReceive()
		{
			Byte[] buffer = new Byte[1024];
			while (receiving)
			{
				if (comport.BytesToRead > 0)
				{
					Int32 length = comport.Read(buffer, 0, buffer.Length);
					Array.Resize(ref buffer, length);
					Display d = new Display(DisplayText);
					this.Invoke(d, new Object[] { buffer });
					Array.Resize(ref buffer, 1024);
				}
				Thread.Sleep(16);
			}
		}

 

       在DoReceive方法中的While迴圈條件是當receiving變數值為True的狀態下則進入迴圈，接著使用SerialPort.BytesToRead屬性檢查接收緩衝區內是否有資料，如果有資料則開始使用SerialPort.Read方法接收資料後顯示在畫面的控制項中；在每一次的迴圈最後使用 Thread.Sleep方法讓執行緒稍微休息一下，在無限或長迴圈中使用Thread.Sleep是一個可以讓資源較有機會釋出的小技巧。

 

       在Form.Load事件委派函式中做一點修改，使其產生執行緒來執行自訂的DoReceive方法。

	Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
		comport = New SerialPort("COM5", 9600, Parity.None, 8, StopBits.One)
		If comport.IsOpen = False Then
			comport.Open()
			receiving = True
			t = New Thread(AddressOf DoReceive)
			t.IsBackground = True
			t.Start()
		End If
	End Sub

 

		private void Form1_Load(object sender, EventArgs e)
		{
			comport = new SerialPort("COM5", 9600, Parity.None, 8, StopBits.One);
			if (!comport.IsOpen)
			{
				comport.Open();
				receiving = true;
				t = new Thread(DoReceive);
				t.IsBackground = true;
				t.Start();
			}
		}

      

       這也沒有啥新鮮的，關於Thread的使用方式和之前的 [Serial Port 系列(7) 基本篇 -- 建立一個簡單的純發送程式(多緒型範例)] 差不多，如果不明白的話可以回頭看那篇文中的說明。