Question

I’m using an unbound data grid in Visual Basic. I made the following loop for the purpose of searching each cell and each column for a duplicate value. But for some reason I get a “InvalidCastException” when I try to add a second row.

Can anyone help?

Private Sub AddJudgeBtn_Click(sender As System.Object, e As System.EventArgs) Handles AddJudgeBtn.Click

    Dim exists As Boolean

    ' ToDo: If the value entered is already on the list, don't add again.

    If JudgeList.Rows.Count() > 0 Then
        For Each itm As DataGridViewRow In JudgeList.Rows
            If itm.Cells("JudgeIDNumber").Value = JudgeIDTxt.Text Then
                exists = True
            End If
        Next
    End If

    If exists = False Then
        Dim AddJudge As String()
        Try
            If JudgeList.Rows.Count = 0 Then
                ' There are no judges, by default. These person becomes the head judge.
                AddJudge = {"0", "HJ", JudgeIDTxt.Text, JudgeNameLbl.Text}
                JudgeList.Rows.Add(AddJudge)
            Else
                ' There is already a judge/head judge, this person becomes a regular judge.
                AddJudge = {"2", "J", JudgeIDTxt.Text, JudgeNameLbl.Text}
                JudgeList.Rows.Add(AddJudge)
            End If

        Catch ex As Exception
            ' Do Nothing
        End Try
    End If
    JudgeIDTxt.Clear()
End Sub

EDIT: Adding the entire click event.

Answer 1

A possible explanation is that your JudgeList DataTable does not consist out of only string values as suggested by this line:

Dim AddJudge As String()

If this is the case then this would be more accurate:

Dim AddJudge As Object()

Also adapt this code reflect the correct data types:

AddJudge = {"2", "J", JudgeIDTxt.Text, JudgeNameLbl.Text}

I am guessing the first parameter should be numeric and not of string type, i.e:

AddJudge = {2, "J", JudgeIDTxt.Text, JudgeNameLbl.Text}

You can also use:

Dim AddJudge As DataRow = JudgeList.NewRow()
JudgeList("JudgeIDNumber") = 2
' update remaining fields...
JudgeList.Rows.Add(AddJudge)

Which will return a data row that is build up with the correct data types for each column.