Question Charting not updating Issue

[martin.s.ransome]

I have a combobox from which the user can select a student, I also have a button from which the user can generate a graph of the student's performance. The graph shows up perfectly but when I select another student and click the button nothing happens. The graph remains the same, no error is thrown.

If you can please Help,

and correct the error in my ways.

 

[JohnH]

Did you use code?

 

[martin.s.ransome]

Yes I did

    Private Sub ButtonGenGraph_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonGenGraph.Click        Dim sqlSelectGrades As String
        Dim strCN As String


        If cn.State = ConnectionState.Closed Then
            strCN = "Data Source=TABS01\TABSDB01;Initial Catalog=SIMS;Persist Security Info=True;User ID=simssysadmin;Password=sims"
            cn.ConnectionString = strCN
            cn.Open()
        End If


        sqlSelectGrades = "SELECT StudentName as Students, avg(grade) Grade FROM studentnames sn, studentgrades sg, subjects s " _
        + " WHERE sn.StudentID = sg.StudentID AND  s.id = sg.subjectid AND s.subjectname = 'Mathematics' AND sn.studentid = " & Me.ComboBoxStudents.SelectedItem.ToString & " group by sn.StudentName " _
        + " UNION SELECT 'Class Average', avg(Grade) FROM studentgrades sg, subjects s WHERE s.id = sg.subjectid AND s.subjectname = 'Mathematics'"


        Dim da As New SqlDataAdapter(sqlSelectGrades, cn)
        Dim ds As New DataSet


        da.Fill(ds, "StudentGrades")


        Dim ChartArea1 As New ChartArea
        Dim chart1 As New Chart
        Dim Legend1 As Legend = New Legend()
        Dim Series1 As Series = New Series()




        Me.Controls.Add(chart1)


        ChartArea1.Name = "ChartArea1"
        chart1.ChartAreas.Add(ChartArea1)
        Legend1.Name = "Legend1"
        chart1.Legends.Add(Legend1)
        chart1.Location = New System.Drawing.Point(100, 250)
        chart1.Name = "Chart1"
        Series1.ChartArea = "ChartArea1"
        Series1.Legend = "Legend1"
        Series1.Name = "Series1"
        chart1.Series.Add(Series1)
        chart1.Size = New System.Drawing.Size(800, 400)
        chart1.TabIndex = 0
        chart1.Text = "Chart1"


        chart1.Series("Series1").XValueMember = "Students"
        chart1.Series("Series1").YValueMembers = "Grade"


        chart1.DataSource = ds.Tables("StudentGrades")


        'chart1.Visible = True
    End Sub

 

[JohnH]

You are creating a new Chart control each click, which next gets behind the previous. Either use the existing control, or Dispose it before adding a new one. Former option is probably best, where you replace most of that code by simply configuring the control in designer. After setting datasource call charts methods DataBind and Update.

 

[martin.s.ransome]

OK So I have found these:

chart1.Series.Dispose()        chart1.Series.Clear()
        chart1.ChartAreas("ChartArea1").Dispose()

But I imagine that I have to test whether or not the series has data and how do I do that?

 

[JohnH]

Why do that? You aren't changing any series or ChartAreas so why destroy it.

 

[martin.s.ransome]

I do not know if this was posted cause I'm not seeing it so I'm gonna say it again. dotnet newbie, VB6 Expert. I do not have a clue. Please assist.

Thank you.

 

[JohnH]

Configure your Chart in designer. In ButtonGenGraph click handler get data, set DataSource, then call the charts DataBind and Update methods.

 

[martin.s.ransome]

ok I'm gonna try. tyvm

 

[martin.s.ransome]

I got it to work. Thank you John for your kind assistance.