Question

每次我尝试连接数据库时，都会给我error "The ConnectionString property has not been initialized"

How can i avoid this error and make it work?

以下是我的代码：

Imports System.Data.OleDb
Public Class frmLoginPage
Dim con As New OleDbConnection
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim dt As New DataTable
    Dim ds As New DataSet
    ds.Tables.Add(dt)
    Dim da As New OleDbDataAdapter

    da = New OleDbDataAdapter("Select*from tblPassword", con)
    da.Fill(dt)

    Dim newRow As DataRow = dt.NewRow
    With newRow
        If .Item("Username") = txtUsername.Text And .Item("Password") = txtPassword.Text Then frmMainMenu.ShowDialog() Else MsgBox("The username or password you entered was incorrect, please try again!", MsgBoxStyle.Critical, "Information")
    End With
End Sub

Answer 1

您已实例化OleDbConnection对象，但尚未设置connectionstring属性，因此它不知道应该连接到何处。你还没有打开它。您的代码应该类似于：

Dim myConnection As OleDbConnection = New OleDbConnection()
myConnection.ConnectionString = myConnectionString
myConnection.Open()
' execute queries, etc
myConnection.Close()

Answer 2

此问题在您不考虑建立新连接时发生解决方案非常简单，您所要做的就是制作

Dim conString as string = "Your connection string here"

Dim con As new OleDbConnection
con.connectionSting= ConSting
con.open()
      'now simply write the query you want to be executed


'At the end write
con.close()

这将解决您的问题。如果它没有解决你的问题，我会尝试解决它。

Answer 3

您从未将连接字符串分配给连接对象，就像错误所说的那样。

在con.open之前插入设置连接字符串的行。

Con.connectionstring =连接 Con.Open（）或者更好的是，更改您的使用声明如下

Dim Connection As String =“Data Source =。\ SQLEXPRESS; AttachDbFilename = G：\ VB Project \ Library Catalog System \ Library Catalog System \ library.mdf; Integrated 安全性=真;连接超时= 30;用户实例=真“

使用Con As New SqlConnection（连接）

“VBS中的ConnectionString属性尚未初始化”错误

3 个答案: