Question

Public Class frmAddB
    Dim con As New OleDb.OleDbConnection
    Dim sql As String
    Dim da As OleDb.OleDbDataAdapter
    Dim ds As New DataSet

    Private Sub frmAddB_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\ATE THESS\Documents\School xD\2-1\VB\VB.accdb"
        Try
            con.Open()
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        Me.Close()
        frmBookMngmt.Show()
    End Sub

    Private Sub btnSave_Click(sender As Object, e As EventArgs) Handles btnSave.Click
        sql = "INSERT INTO [All] (ISBN, Author, Title, PlaceOfPublication, Publisher, Location, Edition, CallNumber) VALUES ('" & txtISBN.Text & "', '" & txtAuthor.Text & "', '" & txtTitle.Text & "', '" & txtPlace.Text & "', '" & txtPub.Text & "', '" & txtLoc.Text & "', '" & txtEd.Text & "', '" & txtCallNo.Text & "')"
        da.InsertCommand = New OleDb.OleDbCommand(sql, con)
        da.InsertCommand.ExecuteNonQuery()
        MsgBox("Book Added!")
        frmBookMngmt.updateDataGridValues()
    End Sub
End Class

每当我点击“保存按钮”时，会出现一个窗口

WindowsApplication1.exe中出现未处理的“System.NullReferenceException”类型异常

附加信息：对象引用未设置为对象的实例。“

出现

，它指向

行

da.InsertCommand = New OleDb.OleDbCommand(sql, con)

任何人都可以帮助我吗？感谢

Answer 1

在您的示例中，您似乎永远不会实例化变量da。

那么也许你也应该尝试改变变量的范围。我想知道每次要访问数据库时都要创建一个新连接。在您的代码中，如果例如frmAddB_Load失败，它可能会处于不可用状态。

对象引用未设置为对象VB.Net，ADO.Net的实例

1 个答案: