从VB.net中的数据库读取更新的记录

Question

I am using VB.Net to read a field from a table in a database. A timer is scheduled to read the value of that field per 5 seconds. I am using a data adapter to get the values in a table , first element of first row in that table is my data. What I observe is that if I read the data in a for loop it works fine. The changes made in that field value externally are reflected in the variable used to store that data. But if I directly read the index 0 element of first row, variable does not reflect changes made externally to database.

'----declaration---
 Dim query2 As String = "SELECT Data2 FROM DSSControl WHERE StationID LIKE 1"
 Dim MDBConnString_ As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=F:\DrumScanningSystem.mdb;;"
Dim ds As New DataSet
Dim cnn As OleDbConnection = New OleDbConnection(MDBConnString_)

'-----use in timer


If cnn.State = ConnectionState.Closed Then
            cnn.Open()
        End If

        Dim cmd1 As New OleDbCommand(query2, cnn)
        Dim da2 As New OleDbDataAdapter(cmd1)
        da2.Fill(ds, "DSSControl")

        Dim t2 As DataTable = ds.Tables("DSSControl")
        Dim row2 As DataRow

        Dim flagvar As UInteger

        For Each row2 In t2.Rows
            flagvar = CUInt(row2(0))
        Next

this works fine but instead of for loop if i use

     row2 = t2.Rows(0) 

     flagvar = CInt(row2(0))

this does not reflect change in 'flagvar' Thanks in advance!

Answer 1

please Correct to flagvar = CUInt(row2(0)) , you lose data with flagvar = CInt(row2(0)) .Perhaps this is the issue

(INTEGER

Integer (whole number) data from -2^31 (-2,147,483,648) through 2^31 - 1 (2,147,483,647). Storage size is 4 bytes.

UINTEGER

Unsigned integer (whole number) data from 0 through 2^32 (4294967295) Storage size is 4 bytes.)

Probably you are interested in non-negative values