未调用“MultiUserChat.addInvitationListener”

我正在研究一个群聊过程。我已成功发送邀请并使用 PSI 收到此邀请。但M无法调用我自己的“MultiUserChat.addInvitationListener“。我已经做了很多方法，但都是徒劳。这是我的尝试之一。

ProviderManager pm = ProviderManager.getInstance();
pm.addExtensionProvider("x", "http://jabber.org/protocol/muc#user", new MUCUserProvider());
MultiUserChat.addInvitationListener(mXmppConnection, MyClass.this);

并做“MyClass extends Activity implements InvitationListener"

@Override
public void invitationReceived(final Connection conn,final String room, final String inviter, String reason, String password, Message message) {
    AlertDialog.Builder builder = new AlertDialog.Builder(MyClass.this);

    builder.setTitle("Room Invitation");
    builder.setMessage(inviter + " sent you an invitation to join GroupChat saying  \""+reason+" \". \n Do you want to join "+inviter+"?");
    builder.setPositiveButton("Accept", new DialogInterface.OnClickListener() {

        // Joining Room
        @Override
        public void onClick(DialogInterface dialog, int which) {

            try {
                MultiUserChat   multiUserChat = new MultiUserChat(conn, room);
                multiUserChat.join(myNickName);
                if(multiUserChat.isJoined()){
                            dialog.cancel();
                }

            } catch (XMPPException e) {
                e.printStackTrace();
            }
        }
    });
    builder.setNegativeButton("Decline", new DialogInterface.OnClickListener() {
        // Declining Room Invitation
        @Override
        public void onClick(DialogInterface dialog, int which) {
            MultiUserChat.decline(conn, room, inviter, "I'm busy right now");
            dialog.cancel();
        }
    });
    builder.show();

}