code modified lines added - vb.net

Question

I have data like this
date value
24sep2014 2:23:01 0.1
24sep2014 2:23:02 0.3
24sep2014 2:23:03 0.2
24sep2014 2:23:04 0.3
These are not coma seprated value. I wanted to write in CSV file. Apend the value for next row.
1)How to open file only once here. when it run next time file name has to change to other name
2) How to append the next values
Imports System
Imports System.IO.Ports
Imports System.ComponentModel
Imports System.Threading
Imports System.Drawing
Imports System.Windows.Forms.DataVisualization.Charting
Public Class Form1
Dim myPort As Array
Dim Distance As Integer
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
myPort = IO.Ports.SerialPort.GetPortNames()
PortComboBox.Items.AddRange(myPort)
BaudComboBox.Items.Add(9600)
BaudComboBox.Items.Add(19200)
BaudComboBox.Items.Add(38400)
BaudComboBox.Items.Add(57600)
BaudComboBox.Items.Add(115200)
ConnectButton.Enabled = True
DisconnectButton.Enabled = False
Chart1.Series.Clear()
Chart1.Titles.Add("Demo")
'Create a new series and add data points to it.
Dim s As New Series
s.Name = "CURRENT"
s.ChartType = SeriesChartType.Line
End Sub
Private Sub ConnectButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ConnectButton.Click
SerialPort1.PortName = PortComboBox.Text
SerialPort1.BaudRate = BaudComboBox.Text
SerialPort1.Open()
Timer1.Start()
Timer2.Start()
'lblMessage.Text = PortComboBox.Text & " Connected."
ConnectButton.Enabled = False
DisconnectButton.Enabled = True
End Sub
Private Sub DisconnectButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles DisconnectButton.Click
SerialPort1.Close()
DisconnectButton.Enabled = False
ConnectButton.Enabled = True
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
Dim counter As Integer
counter = 0
Try
SerialPort1.Write("c")
System.Threading.Thread.Sleep(250)
Dim k As Double
Dim distance As String = SerialPort1.ReadLine()
k = CDbl(distance)
ListBoxSensor.Text = k
Dim s As New Series
s.Points.AddXY(1000, k)
Chart1.Series.Add(s)
Dim headerText = ""
Dim csvFile As String = Path.Combine(My.Application.Info.DirectoryPath, "Current.csv")
If Not File.Exists(csvFile)) Then
headerText = "Date& time ,Current"
End If
Using outFile = My.Computer.FileSystem.OpenTextFileWriter(csvFile, True)
If headerText.Length > 0 Then
outFile.WriteLine(headerText)
End If
Dim y As String = DateAndTime.Now
Dim x As String = y + "," + distance
outFile.WriteLine(x)
End Using
Catch ex As Exception
End Try
End Sub
Private Sub Relay_ON_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Relay_ON.Click
SerialPort1.Write("1")
End Sub
Private Sub Relay_Off_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Relay_Off.Click
SerialPort1.Write("0")
End Sub
End Class
Here i am opening file again and again. that reason i can store only one value
# steve error

Answer 1

The second parameter of OpenTextFileWriter allows to append instead of overwrite your file.
So it is simply a matter to check if the file exists (so you insert the header names) and then write your data
Dim headerText = ""
Dim csvFile As String = Path.Combine(My.Application.Info.DirectoryPath, "Current.csv")
If Not File.Exists(csvFile) Then
headerText = "Date& time ,Current"
End If
Using outFile = My.Computer.FileSystem.OpenTextFileWriter(csvFile, True)
If headerText.Length > 0 Then
outFile.WriteLine(headerText)
End If
Dim y As String = DateAndTime.Now
Dim x As String = y + "," + distance
outFile.WriteLine(x)
End Using
Notice the Using Statement to be sure to close and dispose the file resource also in case of exceptions.
However given the simple text that need to be written you could also choose to use the method WriteAllText
Dim headerText = ""
Dim csvFile As String = Path.Combine(My.Application.Info.DirectoryPath, "Current.csv")
If Not File.Exists(csvFile) Then
headerText = "Date& time ,Current" & Environment.NewLine
End If
Dim y As String = DateAndTime.Now
Dim x As String = headerText & y & "," + distance & Environment.NewLine
My.Computer.FileSystem.WriteAllText(csvFile, x, True)