ConnectionString 属性尚未初始化的问题 - 编程论坛

程序代码：

Public Class 登陆界面

    Dim objDataAdapter As New SqlDataAdapter

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim sqlstr As String
        sqlstr = "select * from admin admin where userid=' " & Trim(TextBox1.Text) & "'and password='" & Trim(TextBox2.Text) & "'"

        Using connection As New SqlConnection()
            connection.Open()

            Dim da As New SqlDataAdapter(sqlstr, connection)
            Dim ds As New DataSet()
            da.Fill(ds)
            connection.Close()
            Dim t = ds.Tables(0)
            If ds.Tables(0).Rows.Count = 0 Then
                MsgBox("你输入的账号或密码错误！", , "提示")
            Else
                主界面.Show()
                Me.Hide()

            End If

        End Using

提示错误：ConnectionString 属性尚未初始化！登陆验证的问题！如何解决，而且这代码应该有其他问题！求指导啊！！！！急死了，就没人知道吗？发了那么多帖子没人回！