Help with NullReferenceException

[plyable]

Hi there. I made a program that reads data from a device through a serial port which then displays it in a textbox. As the data comes out in ASCII form, I have to filter out the unnecessary parts for it to be useful. Example is shown below.

:8+3423,

to

3423


I have managed to to find the necessary code to perform this filtering. But when used in the program I made I get an error that says "NullReferenceException was unhandled" and that "Object reference not set to an instance of an object". It then suggest that I use the "new" keyword to create an object instance. The codes I use for the filtering is:

steps = output_data.Substring(4)
steps = steps.Substring(0, steps.Length - 2)

I use these as since the position of the ASCII is fixed.

Please advice

Codes for program are as shown below:

Public Class Form1
 
 
    Dim s As String
    Dim output_data As String
    Dim steps As String
    Dim colon8 As String = "Chr(4) & Chr(49) & Chr(49) & Chr(58) & Chr(56) & Chr(5)"
    'code in hex is 04 31 31 3A 38 05
    'code in ASCII is 11:8
 
 
 
 
    Private Sub Activate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Activate.Click
 
        COMPort1.Open()
 
    End Sub
 
    Private Sub Deactivate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Deactivate.Click
 
        COMPort1.Close()
 
    End Sub
 
    Private Sub COMPort1_DataReceived(ByVal sender As System.Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles COMPort1.DataReceived
 
        output_data &= COMPort1.ReadExisting
 
    End Sub
 
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
 
        Timer1.Enabled = Not Timer1.Enabled
 
    End Sub
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
 
        COMPort1.Write(Chr(4) & Chr(49) & Chr(49) & Chr(58) & Chr(56) & Chr(5))
 
 
        steps = output_data.Substring(4)
        steps = steps.Substring(0, steps.Length - 2)
        TextBox1.Text() = steps
        steps = ""
 
 
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
 
 
    End Sub
End Class
 

[Plater]

I see this as a problem:
TextBox1.Text() = steps

It should be:
TextBox1.Text = steps


Although I would recomend otherways of filtering out the data, your substring seems to be ok. But it could throw index out of range exceptions if not as much data came in as you think shoud have.

[plyable]

Thanks for the reply. I manage to find out how to fix the problem, though I do not understand why doing so fixes the problem. Apparently I cannot declare

count = count.Substring(4)
count = count.Substring(0, count.Length - 2)
 

in my timer toolbox, but in my comport toolbox. After fixing it. the codes look like this:

Public Class Form1
 
    Dim display As String
    Dim degree As Integer
    Dim output_data As String
    Dim count As String
    Dim colon8 As String = "Chr(4) & Chr(49) & Chr(49) & Chr(58) & Chr(56) & Chr(5)"
    'code in hex is 04 31 31 3A 38 05
    'code in ASCII is 11:8
 
 
 
 
    Private Sub Activate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Activate.Click
 
        If COMPort1.IsOpen Then
            If Timer1.Enabled Then
                Timer1.Stop()
            End If
            COMPort1.Close()
            Activate.Text = "Turn On"
        Else
            COMPort1.Open()
            Activate.Text = "Turn Off"
        End If
 
 
 
 
    End Sub
 
    Private Sub Deactivate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Deactivate.Click
 
        Application.Exit()
 
    End Sub
 
    Private Sub COMPort1_DataReceived(ByVal sender As System.Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles COMPort1.DataReceived
 
        output_data &= COMPort1.ReadExisting()
        'output_data &= COMPort1.ReadLine()
        'supposedly the best way to read data
 
 
        count = output_data
        count = count.Substring(4)
 
 
        count = count.Substring(0, count.Length - 2)
 
    End Sub
 
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
 
            Timer1.Enabled = Not Timer1.Enabled
 
    End Sub
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
 
 
 
        COMPort1.Write(Chr(4) & Chr(49) & Chr(49) & Chr(58) & Chr(56) & Chr(5))
 
        TextBox1.Text = display
 
        count = ""
        output_data = ""
    End Sub
 
 
End Class
 
 

So I now have a new problem. Because I am using the command ReadExisting, My data is read into my software in two phases. All this while I have been using the '&=' to combine the data together, but apparently there is the possibility of me losing data that way. So I was wondering if you could show me how to use ReadLine as it seems that it is the best way to read data. I have not been sucessful so far as when I use that command, the software hangs. I was told that I need a LF at the end of my data to get it to work.

My data is basically ASCII, and will normally look like this:

:8+63632

the last two symbols do not look like LF to me so I do not know if I am misunderstanding something.

What should I consider?

[Plater]

Read line looks for the character string provided to the SerialPort object (there's a property for it in there, line terminator or something) and will continue to try and read data until it encounters that character string.
You would need to find out exactly what character code those last bytes are and use THAT as your line terminator. Then calling ReadLine() will block until it gets an instance of those characters. (Be sure to set ReadTimeOuts if you don't want to wait forever)