如何在私有模块中创建公共变量

基本上这是一个登录表单，我试图保存ID为Me.CBOUsername.Column（0），但是当我尝试以另一种形式调用它时出现错误。

Option Compare Database
Option Explicit
Public ID_ As String
Private Sub Command4_Click()
    Dim strCBOPass As String
    Dim strPassword As String

    strCBOPass = Me.CBOUsername.Column(1)
    strPassword = Me.txtpassword

    If strCBOPass = strPassword Then
        MsgBox "Login Successful!"
        DoCmd.OpenForm "Form1"
        DoCmd.Close acForm, Me.Name
        ID_ = Me.CBOUsername.Column(0)

    Else
        MsgBox "login Unsuccessful!"
    End If
End Sub