Question

我正在本地主机上运行openfire服务器， Smack版本4.2.4在getAllContacts（）方法中获取异常。下面是我的XmppConnection类的代码，该代码扩展了org.jivesoftware.smack.ConnectionListener类。

  public class XmppConnection implements ConnectionListener{
  private  XMPPTCPConnection mConnection;

  public List<Contact> getAllContacts() throws SmackException.NotLoggedInException, InterruptedException, SmackException.NotConnectedException {

    Log.d(TAG,"getAllContats called()");
    List<Contact> contacts = new ArrayList<>();

    if(XmppConnectService.sConnectionState == ConnectionState.AUTHENTICATED){
        Roster roster = Roster.getInstanceFor(mConnection);  //exception here

            Collection<RosterEntry> entries = roster.getEntries();
            Presence presence;

            for (RosterEntry entry : entries) {
                Contact c = new Contact(entry.getJid().toString());
                presence = roster.getPresence(entry.getJid());

                contacts.add(c);
                       }


    return contacts;

}

public XmppConnection( Context context)
{

    mApplicationContext = context.getApplicationContext();
    String jid = PreferenceManager.getDefaultSharedPreferences(mApplicationContext)
            .getString("xmpp_jid",null);
    mPassword = PreferenceManager.getDefaultSharedPreferences(mApplicationContext)
            .getString("xmpp_password",null);

    if( jid != null)
    {
        mUsername = jid.split("@")[0];
        mServiceName = jid.split("@")[1];
    }else
    {
        mUsername ="";
        mServiceName="";
    }
}


public void connect() throws IOException,XMPPException,SmackException
{
    Log.d(TAG, "Connecting to server " + mServiceName);

    InetAddress addr = InetAddress.getByName(OPENFIRE_HOST);

    HostnameVerifier verifier = new HostnameVerifier() {
        @Override
        public boolean verify(String hostname, SSLSession session) {

            return true;
        }
    };


    DomainBareJid serviceName = JidCreate.domainBareFrom(OPENFIRE_HOST);
    conf = XMPPTCPConnectionConfiguration.builder();
            conf.setXmppDomain(serviceName
            .setHostAddress(addr)
            .setUsernameAndPassword(mUsername,mPassword)
            .setPort(5222)
            .setHostnameVerifier(verifier)
                                      .setSecurityMode(ConnectionConfiguration.SecurityMode.required)

            .setSecurityMode(ConnectionConfiguration.SecurityMode.disabled)
            .setCompressionEnabled(true);

    mConnection = new XMPPTCPConnection(conf.build());

    setupUiThreadBroadCastMessageReceiver();

    mConnection.addConnectionListener(this);
    try {

         mConnection.connect();

        mConnection.login(mUsername,mPassword);


    } catch (InterruptedException e) {
        e.printStackTrace();

    }


    ReconnectionManager reconnectionManager = ReconnectionManager.getInstanceFor(mConnection);
    reconnectionManager.setEnabledPerDefault(true);
    reconnectionManager.enableAutomaticReconnection();

    }

}

@Override
public void connected(XMPPConnection connection) {
    XmppConnectService.sConnectionState = ConnectionState.CONNECTED;
    Log.w(TAG,"Connected Successfully; id:" + XmppConnectService.sConnectionState);

}

@Override
public void authenticated(XMPPConnection connection, boolean resumed) {
    XmppConnectService.sConnectionState = ConnectionState.AUTHENTICATED;
    Log.w(TAG,"Authenticated Successfully");
    showContactListActivityWhenAuthenticated();
 }
    }
}

以上代码在logcat中显示此错误：java.lang.NullPointerException: XMPPConnection must not be null

我正在从另一个类中调用getAllContacts（）

XmppConnection xmpp = new XmppConnection(this);
contacts = xmpp.getAllContacts();

getAllContacts（）方法是从另一个活动中调用的，并在authenticated（）方法之后调用。由于它是在authenticated（）方法之后调用的，因此mConnection应该已初始化。

Answer 1

如代码所示，您可以在connect（）方法中初始化mConnection变量。而且您的authenticated（）方法不会对connect（）方法进行任何调用。您能否确保在调用authenticated（）方法之前或在方法内部调用方法connect（）

Answer 2

为XmppConnection类创建新对象会使用null初始化其变量。将XMPPTCPConnection声明为静态可行：

private static XMPPTCPConnection mConnection;

为XMPPConnection获取Nullpointer异常

2 个答案: