Question

在将数据从数据库填充到datagridview时，我需要一种将DBNull转换为字符串的方法。以下是我的代码

 Private Sub FetchData()

    sql = "SELECT ContributionType,Status,PayMethod,BankName,AccountNo,Amount,FullName,District,Refno,ContributorGrp"
    sql &= " FROM tblincome WHERE TxnID=@id"

    command = New OleDbCommand(sql, connection)
    command.Parameters.Add(New OleDbParameter("@id", OleDbType.VarChar)).Value = lbltxnid.Text

    adapter = New OleDbDataAdapter(command)
    dt = New DataTable
    adapter.Fill(dt)



    For Each row In dt.Rows
        PopulateGrid(row(0), row(1), row(2), row(3), row(4), row(5), row(6), row(7), row(8), row(9))
    Next

    dt.Rows.Clear()
    dt.Dispose()
End Sub

Private Sub PopulateGrid(ContributionType As String, Status As String, PayMethod As String, BankName As String _
                         , AccountNo As String, Amount As Double, FullName As String, District As String _
                         , Refno As String, ContributorGrp As String)

    Dim row As String() = New String() {ContributionType, Status, PayMethod, BankName, AccountNo, Amount.ToString("N") _
                                       , FullName, District, Refno, ContributorGrp}
    dgvcontributions.Rows.Add(row)
End Sub

BankName和Accountno字段允许空条目，因此它们最有可能是具有空值的条目。

Answer 1

您可以使用此方法：

Public Shared Function ConvertDbVal(Of T)(obj As Object, Optional nullFallbackVal As T = Nothing) As T
    If obj Is Nothing OrElse obj.Equals(DBNull.Value) Then
        Return nullFallbackVal
    Else
        Return CType(obj, T)
    End If
End Function

用法：

Dim bankName As String = ConvertDbVal(row(3), "")
Dim accNumber = ConvertDbVal(row(4), "")

如果您没有指定（可选）后备值，则必须明确指定类型：

Dim bankName As String = ConvertDbVal(Of String)(row(3))

在将数据填充到Datagridview之前将DBNull转换为字符串

1 个答案: