n          IsNull方法

n          Overloads Public Function IsNull(ByVal column As DataColumn ) As Boolean

n          Overloads Public Function IsNull(ByVal columnIndex As Integer ) As Boolean

n          Overloads Public Function IsNull(ByVal columnName As String ) As Boolean

n          Overloads Public Function IsNull(ByVal column As DataColumn, ByVal version As DataRowVersion ) As Boolean

参数

1.         column DataColumn。

2.         columnIndex 列的从零开始的索引。

3.         columnName 列的名称。

4.         version DataRowVersion 值之一，它指定行版本。可能值为 Default、Original、Current 和 Proposed。

示例1

以下示例将列的值更改为空值，然后使用 IsNull 方法来确定该值是否为空。

Private Sub IsValNull()

   Dim t As DataTable

   Dim r As DataRow

   '''' Assuming the DataGrid is bound to a DataTable.

   t = CType(DataGrid1.DataSource, DataTable)

   r = t.Rows(datagrid1.CurrentCell.RowNumber)

   r.BeginEdit

   r("FirstName") = System.DBNull.Value’ r(1) = System.DBNull.Value

   r.EndEdit

   r.AcceptChanges

   Console.WriteLine(r.IsNull("FirstName"))’ Console.WriteLine(r.IsNull(1))

End Sub

示例2

Private Sub PrintRows(ds As DataSet)

    Dim t As DataTable

    Dim c As DataColumn

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