Question

我不知道我怎么能在程序中修正错误...问题是con.open（）

Private Sub btnadd1_Click(ByVal sender As System.Object, _
   ByVal e As System.EventArgs) Handles btnadd1.Click

Dim cmd As New OleDb.OleDbCommand
Dim con As New OleDb.OleDbConnection
Dim Printlist1 As New DataTable

If Not con.State = ConnectionState.Open Then 
   con.Open()
   cmd.Connection = con
End If

    If Me.text1.Tag & "" = "" Then
        cmd.CommandText = "INSERT INTO Datagrid1(StickerCode, Description, Company, Department, Location, User, SerialNumber, DatePurchased, Tagable, Quantity, Brand, Model ) " & _
                        " VALUES(" & Me.text1.Text & ",'" & Me.text2.Text & "','" & _
                            Me.text3.Text & "','" & Me.text4.Text & "','" & Me.text5.Text & "','" & _
                            Me.text6.Text & "','" & Me.text7.Text & "','" & Me.text8.Text & "','" & _
                            Me.text9.Text & "','" & Me.text10.Text & "','" & Me.text11.Text & "','" & _
                            Me.text12.Text & "')"

        cmd = New OleDbCommand(cmd.CommandText, con)
        cmd.ExecuteNonQuery()
    Else


        cmd.CommandText = "UPDATE Form4 " & _
                    " SET StickerCode='" & Me.text1.Text & _
                    ", Description='" & Me.text2.Text & "'" & _
                    ", Company='" & Me.text3.Text & "'" & _
                    ", Department='" & Me.text4.Text & "'" & _
                    ", Location='" & Me.text5.Text & "'" & _
                    ", User='" & Me.text6.Text & "'" & _
                    ", SerialNumber='" & Me.text7.Text & "'" & _
                    ", DatePurchased='" & Me.text8.Text & "'" & _
                    ", Tagable='" & Me.text9.Text & "'" & _
                    ", Quantity='" & Me.text10.Text & "'" & _
                    ", Brand='" & Me.text11.Text & "'" & _
                    ", Model='" & Me.text12.Text & "'" & _
                    " WHERE text1=" & Me.text1.Tag


        cmd.ExecuteNonQuery()

    End If
    RefreshData()
    Me.btnclear1.PerformClick()
    con.Close()

End Sub

Answer 1

您还没有将连接字符串传递给您的连接对象，因此它不知道要打开哪个数据库或在哪里找到它。

试试这个：

Dim con As New OleDb.OleDbConnection("My connection string")

Answer 2

您没有为OleDbConnection对象提供连接字符串。连接字符串告诉OleDbConnection对象您希望它连接到哪个数据库。您可以在构造函数中为它提供连接字符串，如下所示：

Dim con As New OleDb.OleDbConnection(connectionString)

或者，您可以通过ConnectionString属性设置它，如下所示：

Dim con As New OleDb.OleDbConnection()
con.ConnectionString = connectionString

实际连接字符串的格式因数据库引擎和版本而异。但是，网上有大量资源，它们会显示正确的格式以及它可以包含的选项。举个例子，它可能看起来像这样：

Dim connectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb"

更新

很抱歉，如果我通过讨论乱序的步骤让你感到困惑。基本上，您需要做的就是将连接字符串赋予OleDbConnection对象。在调用Open方法之前，您需要这样做。例如，您可以更改以下行：

Dim con As New OleDb.OleDbConnection

对此：

Dim con As New OleDb.OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb")

但是，显然，您需要将连接字符串更改为适合您特定情况的任何内容。上面的例子只是有效连接字符串的示例。

或者，如果您不想立即将连接字符串提供给OleDbConnection对象，您可以稍后再将其提供给它，只要您在调用Open之前设置它即可。。例如，您可以更改以下行：

Dim cmd As New OleDb.OleDbCommand
Dim con As New OleDb.OleDbConnection
Dim Printlist1 As New DataTable
If Not con.State = ConnectionState.Open Then 
    con.Open()
    ' ...

对此：

Dim cmd As New OleDb.OleDbCommand
Dim con As New OleDb.OleDbConnection
Dim Printlist1 As New DataTable
If Not con.State = ConnectionState.Open Then 
    con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb"
    con.Open()
    ' ...

原始示例似乎让您感到困惑，首先将连接字符串存储在变量中，然后将该变量中的值传递给连接对象，如下所示：

Dim connectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=c:\MyDb.mdb"
Dim con As New OleDb.OleDbConnection(connectionString)

ADO.NET：ConnectionString属性尚未初始化

2 个答案:

更新