空值异常 - Vb.Net

Question

  Private Sub Button4_Click_1(sender As Object, e As EventArgs) Handles Button4.Click
    Dim ConnString As String = "Provider=Microsoft.Jet.OLEDB.4.0;" & "Data Source=" & TextBox1.Text
    Dim SQLString As String = "SELECT * FROM " & ComboBox1.Text
    Dim OleDBConn1 As System.Data.OleDb.OleDbConnection = New System.Data.OleDb.OleDbConnection(ConnString)
    Dim DataSet1 As New DataSet()
    Dim OleDbDataAdapter1 As System.Data.OleDb.OleDbDataAdapter = New System.Data.OleDb.OleDbDataAdapter(SQLString, OleDBConn1)
    OleDBConn1.Open()
    OleDbDataAdapter1.Update(DataSet1.Tables(ComboBox1.Text))
    DataSet1.AcceptChanges()
    OleDBConn1.Close()
End Sub

此代码在更新时引发空值异常

Answer 1

Dim DataSet1 As New DataSet()
Dim OleDbDataAdapter1 As System.Data.OleDb.OleDbDataAdapter = New System.Data.OleDb.OleDbDataAdapter(SQLString, OleDBConn1)
OleDBConn1.Open()
OleDbDataAdapter1.Update(DataSet1.Tables(ComboBox1.Text))

在这四行中的第一行中，您正在创建一个 DataSet，在第四行中，您尝试通过名称从中获取一个 DataTable。中间的两行究竟是如何神奇地在 DataSet 中创建 DataTable 的？答案是他们没有。大概你已经有一个包含所需 DataTable 的 DataSet，所以使用它。

空值异常 - Vb.Net

Null value Exception- Vb.Net

database

vb.net

oledb

ms-access