MqttServerGetAllRetainTopics 方法

获取所有的驻留的消息的主题，如果消息发布的时候没有使用Retain属性，就无法通过本方法查到
Get the subject of all resident messages. If the Retain attribute is not used when the message is published, it cannot be found by this method

public string[] GetAllRetainTopics()

Public Function GetAllRetainTopics As String()

public:
array<String^>^ GetAllRetainTopics()

member GetAllRetainTopics : unit -> string[]