取消订阅某个主题

Private Sub Unsubscribe()
On Error GoTo errExit
    Dim retCode As MqttUnsubscriptionCode
    Dim unSubOption As MQTTUnsubscribeOption
    
    Set unSubOption = mFactory.CreateUnsubscribeOption
    unSubOption.Topic = "SE"
    retCode = mClient.Unsubscribe(unSubOption)
    Exit Sub
    
errExit:
    MsgBox Err.Description
End Sub