使用MySql调用Read（）之前尝试访问字段无效

Question

I am trying to run this code, but this error always pops up when I click on data grid view.

What do you think is the error here?

Private Sub dgvRecords_CellClick(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles dgvRecords.CellClick
    Dim intID As Integer
    Try
        Integer.TryParse(dgvRecords.Item(0, dgvRecords.CurrentRow.Index).Value, intID)
        Dim dbQuery As String = "Select * from tblstudents where id = " & intID
        Dim dbConnection As New MySqlConnection(dbConString)
        Dim dbCmd As New MySqlCommand(dbQuery, dbConnection)
        Dim dbReader As MySqlDataReader
        dbConnection.Open()
        dbReader = dbCmd.ExecuteReader()

        txtStudID.Text = dbReader("id")
        txtLastname.Text = dbReader("lastname")
        txtFirstname.Text = dbReader("firstname")
        txtMiddlename.Text = dbReader("middlename")
        txtAddress.Text = dbReader("address")
        cmbGender.Text = dbReader("gender")
        txtContact.Text = dbReader("contact")
        cmbCivilStatus.Text = dbReader("civil_status")

        dbReader.Close()
        dbConnection.Close()
    Catch ex As Exception
        MsgBox("ERROR: " & ErrorToString(), MsgBoxStyle.Critical)
    End Try
End Sub

Answer 1

You are getting that error cause you are not calling the Read() method on reader object and without which reader object can't advance to the firs row in result set to start fetching. That's what the error says exactly. You should do like

While(dbReader.Read())
{
  txtStudID.Text = dbReader("id")
  txtLastname.Text = dbReader("lastname")
  .......
}