connectionstring属性尚未初始化vb.net

Question

连接字符串属性尚未初始化。这是我的代码：

Imports System.Data.OleDb
Imports System.Data

Public Class Main_DB

    Dim cnn As OleDbConnection = New OleDbConnection()

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        Using cnn = New OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=G:\PD\Data.accdb")
            Using cmd = New OleDbCommand()
                cnn.ConnectionString = cmd.CommandText

                If Not cnn.State = ConnectionState.Open Then

                    cnn.Open()
                End If

                cnn.Close()
                cmd.Connection = cnn

                cmd.Connection = cnn
                cmd.CommandText = "INSERT INTO [database] ([Name], [Address], [EPF])" & _
                                  "VALUES(" & Me.txtname.Text & ",'" & Me.txtadd.Text & "','" & Me.txtPF.Text & "'cnn)"

                cmd.ExecuteNonQuery()


                cnn.Close()
            End Using
        End Using
    End Sub
End Class