Question

Preamble:
Having not worked with WinForms for a long while and also never before in VB I am trying to add a DataGridView to an application written in VB which will display a grid of data from a DataTable.

I followed the documentation here, here and here and in a simple test example I have the code

Public Class Form1

    Private count As Integer

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        count = count + 1

        Dim table As DataTable = BindingSource2.DataSource

        Dim row As DataRow
        row = table.NewRow()
        row("Col1") = "foo" + count.ToString()
        row("Col2") = "bar" + count.ToString()

        table.Rows.Add(row) 'throws System.InvalidOperationException here

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        'BindingSource2.DataSource = New DataTable()
        'Dim table As DataTable = BindingSource2.DataSource
        Dim table As New DataTable

        Dim column1 As DataColumn = New DataColumn()
        column1.ColumnName = "Col1"
        column1.Caption = column1.ColumnName
        column1.DataType = System.Type.GetType("System.String")
        table.Columns.Add(column1)

        Dim column2 As DataColumn = New DataColumn()
        column2.ColumnName = "Col2"
        column2.Caption = column2.ColumnName
        column2.DataType = System.Type.GetType("System.String")
        table.Columns.Add(column2)

        'Dim keys(0) As DataColumn
        'keys(0) = column1
        'table.PrimaryKey = keys

        ' first row
        Dim row As DataRow = table.NewRow()
        row("Col1") = "beep"
        row("Col2") = "boop"

        table.Rows.Add(row)

        BindingSource2.DataSource = table
    End Sub
End Class

The code gets through Form1_Load okay however the entries added there are not shown in the DataGridView. Then when Timer1_Tick is called it throws a System.InvalidOperationException exception at the line indicated above. I cannot see what I am doing wrong based on the examples given in the docs.

Question: Can anybody help please, with (a) why does the DataGridView not reflect the added data at the end of Form1_Load and (b) why is adding a row causing an exception?

P.s. I’ve checked the debug and at the table.Rows.Add(row) table contains the correct information as does row.

Edit: The BindingSource was added and connected to the DataGridView using the designer so the code for it is shown instead in From1.Designer.vb which I haven’t shown here.

Answer 1

The solution (at least in my case here) was that the DataGridView.AutoGenerateColumns is not shown in the design panel and is by default set to False. I simply added the line

DataGridView1.AutoGenerateColumns = True

to my code (in Form1_Load) and it worked perfectly. I found the solution on a forum but now cannot find the link. I’ll add it if I find it.