ConnectionString属性尚未初始化。错误？

Imports System.Data.OleDb

Public Class Money_Donated
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        All_Donations.Show()
        Me.Close()
        provider = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="
        dataFile = "C:\Users\Derick\Desktop\ICE 9\Donors.accdb"

    End Sub

    Dim provider As String
    Dim dataFile As String
    Dim connString As String
    Public dr As OleDbDataReader

    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click
        Dim myConnection As OleDbConnection = New OleDbConnection()
        myConnection.ConnectionString = connString
        connString = provider & dataFile
        TextBox1.Clear()
        myConnection.Open()
        Dim str As String
        str = "SELECT * FROM Donors WHERE (Code = '" & Donators121.Amount_of_money_donatedTextBox.Text & "')"
        Dim cmd As OleDbCommand = New OleDbCommand(str, myConnection)
        dr = cmd.ExecuteReader
        myConnection.Close()
        While dr.Read()
            TextBox1.Text = dr("Description").ToString
        End While
    End Sub
End Class
Imports System.Data.OleDb

Public Class Money_D