[RESOLVED] SrialPort readbyte to a Byte array failure

[pourkascheff]

Hello all, following code will cause "Index was outside the bounds of the array." as exception:

Public Class MainWindow
    Dim RxBuffer As Byte() = {}
        Try
            If SerialPort1.BytesToRead <> 0 Then
                For index = 0 To SerialPort1.BytesToRead - 1
                    RxBuffer(index) = SerialPort1.ReadByte
                Next
            End If
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical)
            Application.Exit()
        End Try
End Class

What I tried:
- Switching variable to other type(s).
- Adding/removing "()" and "{}".
- Adding/removing "index + 1" and "index - 1".

Adding "SerialPort1.ReadByte" in a textbox control once a loop works properly for whole data:

TextBox1.Text = TextBox1.Text & SerialPort1.ReadByte & " "

The goal is to store received bytes in an array to call/change in-application then clear it every time. The length is changeable every time.
Thanks for contribution in advanced.

[jmcilhinney]

If you expect to read N Bytes and assign them to the elements of an array then you need to have an array and you need that array to have at least N elements. Here:

Dim RxBuffer As Byte() = {}

you are creating an array with zero elements, so of course any index you specify will be out of range. The obvious thing to do is to create an array at the point you know how many elements it will need:

Private buffer As Byte()

and:

Dim byteCount = SerialPort1.BytesToRead
 
If byteCount > 0 Then
    buffer = New Byte(byteCount - 1) {}
 
    For i = 0 To byteCount
        buffer(i) = SerialPort.ReadByte()
    Next
End If

Alternatively, use a List(Of Byte) and call Add, letting it grow as required. You can then call ToArray at the end if you specifically need an array.

[jmcilhinney]

That said, why read the data Byte by Byte when the SerialPort has a Read method that will read multiple Bytes at a time? You can either create an array big enough to contain all the data and read it all in one go:

Dim byteCount = SerialPort1.BytesToRead
 
If byteCount > 0 Then
    buffer = New Byte(byteCount - 1) {}
 
    SerialPort.Read(buffer, 0 byteCount)
End If

or you can use a fixed-size buffer and read the data in chunks. That's how you generally read large data streams or data for which you don't know the size. I'll leave that to you as an exercise, noting that Read will return the number of Bytes read and that being less than the number of Bytes you specified to read means that there's no more data.

[pourkascheff]

That said, why read the data Byte by Byte when the SerialPort has a Read method that will read multiple Bytes at a time?

What a fantastic idea! To be honest I didn't give a chance to try 'Read' method once. I'm using Serial Port in an external microcontroller low-level based stream. (Mostly Modbus RTU and creating a 16 bit values from (EvenByte*255)+OddByte)

Private buffer As Byte()

Rectifies the matter, sir.

I believe a comma is needed @ line #6 in last code 'Read' argument. 3:')

Since we got here, Please introduce the best way you know for an always ready to read port. I mean is there any "DataReceived" event or something to use cause I use a 1mS timer to do such thing (If byteCount > 0 Then communication is online and Rx is coming)

[pourkascheff]

And two more questions:
1) How to get that "buffer" from "Private buffer As Byte()" length after all work? (.Length.toString and .GetLength doesn't work)
2) Didn't want to get it from SerialPort1.BytesToRead because I want to figure out what is happening due to exception which is happening when I stream a non-stop data with such message: "Index was outside the bounds of the array.". Is there a way to clear that "buffer" every cycle?

[dbasnett]

My approach to SerialPorts is different than most. I tend to have a small received event handler that accumulates bytes and a separate process that enforces protocol.

See: https://www.vbforums.com/showthread....=1#post5568506