VS 2015 problem in plotting graph on a picturebox in visual studio 2015 vb.net-VBForums
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Thread: problem in plotting graph on a picturebox in visual studio 2015 vb.net

  1. #1

    Thread Starter
    Registered User
    Join Date
    Jan 2018

    problem in plotting graph on a picturebox in visual studio 2015 vb.net

    Hello everyone,
    actually i am plotting a real time graph on a picturebox of a windows form but after plotting some right values my cursor automatically drops to 0 and starts plotting graph from there. The real time values are processed by an micro controller and and communicated to pc via serial communication..... So plz help me to get out of this problem... i shall be very thankfull to all of you..... i am attaching my code and screenshots below.. Name:  error.jpg
Views: 129
Size:  27.7 KB[CODE]

            Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
            conn.ConnectionString = "Data Source =C:\Users\Chauhan\Desktop\PatientDB.db;version = 3"
            PictureBox1.BackColor = Color.White
            PictureBox2.BackColor = Color.White
            myPort.PortName = "COM4"
            myPort.BaudRate = 9600
            myPort.Parity = Parity.None
            myPort.DataBits = 8
            myPort.StopBits = StopBits.One
            myPort.Encoding = Encoding.ASCII
        End Sub
        Private Sub myPort_DataReceived(sender As Object, e As SerialDataReceivedEventArgs) Handles myPort.DataReceived
            inData = myPort.ReadByte
            ' numbers1.Enqueue(inData)
            ' Dim myResponse As String = myPort.ReadExisting
            ' UpdateGraph(myResponse)
            DataEnter = True
            ' Yval = inData
            ' PrintX1()
        End Sub
     Function PrintX2(ByVal Xvalue1 As Byte) As Object
            ' PictureBox1.Image = New Bitmap(500, 500)
            '  g1 = Graphics.FromImage(PictureBox1.Image)
            '  Dim gridPen = New Pen(Color.Black, 2)
            '  g1.DrawLine(gridPen, 0, 0, 100, 100)
            x_start = 1
            y_start = PictureBox2.Height - 82
            mygraphics = PictureBox2.CreateGraphics
            ' mygraphics.PageUnit = GraphicsUnit.Pixel
            'mygraphics.PageScale = 1
            ' mygraphics.DrawLine(p1, 0, CInt(PictureBox1.Height), CInt(PictureBox1.Width), CInt(PictureBox1.Height))
            mygraphics.SmoothingMode = Drawing2D.SmoothingMode.HighQuality
            ' mygraphics.ScaleTransform(1, 1)
            If DataEnter = True Then
                mygraphics.SmoothingMode = Drawing2D.SmoothingMode.HighQuality
                mygraphics.DrawLine(p2, x_start + k, y_start - temp_ahead1, x_start + (k + 1), y_start - Xvalue1)
                temp_ahead1 = Xvalue1
                DataEnter = False
                Dr = True
            End If
            k = k + 1
            If k = PictureBox2.Width Then
                k = 0
            End If
        End Function

  2. #2
    .NUT jmcilhinney's Avatar
    Join Date
    May 2005
    Sydney, Australia

    Re: problem in plotting graph on a picturebox in visual studio 2015 vb.net

    Without having looked carefully at your code, there are two major problems.

    Firstly, the DataReceived event is raised on a background thread so you don't do anything from that event handler that directly affects the UI. You need to learn how to marshal a method call to the UI thread.

    Secondly, you never call CreateGraphics. If you want to draw on a control then you do so in its Paint event handler.
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  3. #3
    Super Moderator Shaggy Hiker's Avatar
    Join Date
    Aug 2002

    Re: problem in plotting graph on a picturebox in visual studio 2015 vb.net

    You say that the cursor drops to zero. What does the cursor have to do with anything? If you are plotting data coming from anywhere, you shouldn't be dealing with the cursor. Now, if you meant the drawing point, which isn't the cursor, then how do you know that the zero is wrong? If zero is what you got, then zero is what you should plot. That's the first thing to check (after dealing with the points that JMC made). If you are getting a zero, then the problem isn't in the code. If you are not getting a zero, then you have an excellent start to finding the problem.
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  4. #4
    Addicted Member
    Join Date
    Nov 2011

    Re: problem in plotting graph on a picturebox in visual studio 2015 vb.net

    The updating of graphics can be improved but I will leave that for someone else to help with, what I can help with possibly is the way serial data is captured.

    The first thing I would do is create a delegate that will safely handle the serial data once we have received. So first we declare the delegate and data type we want to handle:

     Public Delegate Sub myDelegate(ByVal inData As Byte)
    Next we create the delegate subroutine where we can safely pass the data received to the main UI thread. You may not need all the values I included here for example.

    Private Sub inDataDelegate(ByVal indata As Byte)
            DataEnter = True
        End Sub
    Finally we keep the code in the DataReceived event handler to a minimum and pass the data bytes out to the delegate subroutine with "BeginInvoke"

     Private Sub myport_DataReceived(sender As Object, e As SerialDataReceivedEventArgs) Handles myport.DataReceived
            myport.ReadTimeout = 20
            Do While myport.BytesToRead > 0
                    Dim inData As Byte = myport.ReadByte
                    Me.BeginInvoke((New myDelegate(AddressOf inDataDelegate)), inData)
                End Try
    	End Sub

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