Android Smack UserSearchManager (java.lang.ClassCastException java.lang.NullPointerException)

用smack 開發IM　聊天工具時, 會用到UserSearchManager 來搜索服務器的聯繫人  判斷用戶是否存在等等，代碼以下：

　　　　 UserSearchManager search = new UserSearchManager(ClientConnectionServer.connection);
        Form searchForm = null;
        try
        {
            searchForm = search.getSearchForm("search." + ClientConnectionServer.connection.getServiceName());         }
        catch (XMPPException e1)
        {
            e1.printStackTrace();
        }
        Form answerForm = searchForm.createAnswerForm();
        answerForm.setAnswer("Username", true);
        answerForm.setAnswer("search", editContact.getText().toString());
        ReportedData data = null;
        try
        {
            data = search.getSearchResults(answerForm, "search." + ClientConnectionServer.connection.getServiceName());
        }
        catch (XMPPException e1)
        {
            e1.printStackTrace();
        }

        String result = "";
        if (null != data && data.getRows() != null)
        {
            Iterator<Row> it = data.getRows();
            Row row = null;
            while (it.hasNext())
            {
                row = it.next();
                String name = row.getValues("Username").next().toString();
                result += name;
            }
        }

此時紅色部分會報 java.lang.NullPointerException, 一種解決辦法是在紅色代碼前加：

ProviderManager.getInstance().addIQProvider("query", "jabber:iq:search", new UserSearch.Provider());

但下面還會報 java.lang.ClassCastException , 國外論壇有人解答時jar 包 引用問題，解決辦法是在XMPPConnection初始化前，加個configure()方法完成一些設置，能夠同時解決上面種異常，代碼爲：

public void configure(ProviderManager pm)
    {

        // Private Data Storage
        pm.addIQProvider("query", "jabber:iq:private", new PrivateDataManager.PrivateDataIQProvider());

        // Time
        try
        {
            pm.addIQProvider("query", "jabber:iq:time", Class.forName("org.jivesoftware.smackx.packet.Time"));
        }
        catch (ClassNotFoundException e)
        {
            Log.w("TestClient", "Can't load class for org.jivesoftware.smackx.packet.Time");
        }

        // Roster Exchange
        pm.addExtensionProvider("x", "jabber:x:roster", new RosterExchangeProvider());

        // Message Events
        pm.addExtensionProvider("x", "jabber:x:event", new MessageEventProvider());

        // Chat State
        pm.addExtensionProvider("active", "http://jabber.org/protocol/chatstates", new ChatStateExtension.Provider());
        pm.addExtensionProvider("composing", "http://jabber.org/protocol/chatstates", new ChatStateExtension.Provider());
        pm.addExtensionProvider("paused", "http://jabber.org/protocol/chatstates", new ChatStateExtension.Provider());
        pm.addExtensionProvider("inactive", "http://jabber.org/protocol/chatstates", new ChatStateExtension.Provider());
        pm.addExtensionProvider("gone", "http://jabber.org/protocol/chatstates", new ChatStateExtension.Provider());

        // XHTML
        pm.addExtensionProvider("html", "http://jabber.org/protocol/xhtml-im", new XHTMLExtensionProvider());

        // Group Chat Invitations
        pm.addExtensionProvider("x", "jabber:x:conference", new GroupChatInvitation.Provider());

        // Service Discovery # Items
        pm.addIQProvider("query", "http://jabber.org/protocol/disco#items", new DiscoverItemsProvider());

        // Service Discovery # Info
        pm.addIQProvider("query", "http://jabber.org/protocol/disco#info", new DiscoverInfoProvider());

        // Data Forms
        pm.addExtensionProvider("x", "jabber:x:data", new DataFormProvider());

        // MUC User
        pm.addExtensionProvider("x", "http://jabber.org/protocol/muc#user", new MUCUserProvider());

        // MUC Admin
        pm.addIQProvider("query", "http://jabber.org/protocol/muc#admin", new MUCAdminProvider());

        // MUC Owner
        pm.addIQProvider("query", "http://jabber.org/protocol/muc#owner", new MUCOwnerProvider());

        // Delayed Delivery
        pm.addExtensionProvider("x", "jabber:x:delay", new DelayInformationProvider());

        // Version
        try
        {
            pm.addIQProvider("query", "jabber:iq:version", Class.forName("org.jivesoftware.smackx.packet.Version"));
        }
        catch (ClassNotFoundException e)
        {
            // Not sure what's happening here.
        }

        // VCard
        pm.addIQProvider("vCard", "vcard-temp", new VCardProvider());

        // Offline Message Requests
        pm.addIQProvider("offline", "http://jabber.org/protocol/offline", new OfflineMessageRequest.Provider());

        // Offline Message Indicator
        pm.addExtensionProvider("offline", "http://jabber.org/protocol/offline", new OfflineMessageInfo.Provider());

        // Last Activity
        pm.addIQProvider("query", "jabber:iq:last", new LastActivity.Provider());

        // User Search
        pm.addIQProvider("query", "jabber:iq:search", new UserSearch.Provider());

        // SharedGroupsInfo
        pm.addIQProvider("sharedgroup", "http://www.jivesoftware.org/protocol/sharedgroup", new SharedGroupsInfo.Provider());

        // JEP-33: Extended Stanza Addressing
        pm.addExtensionProvider("addresses", "http://jabber.org/protocol/address", new MultipleAddressesProvider());

        // FileTransfer
        pm.addIQProvider("si", "http://jabber.org/protocol/si", new StreamInitiationProvider());

        pm.addIQProvider("query", "http://jabber.org/protocol/bytestreams", new BytestreamsProvider());

        // Privacy
        pm.addIQProvider("query", "jabber:iq:privacy", new PrivacyProvider());
        pm.addIQProvider("command", "http://jabber.org/protocol/commands", new AdHocCommandDataProvider());
        pm.addExtensionProvider("malformed-action", "http://jabber.org/protocol/commands", new AdHocCommandDataProvider.MalformedActionError());
        pm.addExtensionProvider("bad-locale", "http://jabber.org/protocol/commands", new AdHocCommandDataProvider.BadLocaleError());
        pm.addExtensionProvider("bad-payload", "http://jabber.org/protocol/commands", new AdHocCommandDataProvider.BadPayloadError());
        pm.addExtensionProvider("bad-sessionid", "http://jabber.org/protocol/commands", new AdHocCommandDataProvider.BadSessionIDError());
        pm.addExtensionProvider("session-expired", "http://jabber.org/protocol/commands", new AdHocCommandDataProvider.SessionExpiredError());
    }