Java NullPointerException致命异常：线程-5023错误

我试图在android上创建一个xmpp/jabber客户端，我正在使用“对话”的开源代码，现在我遇到了以下错误

我尝试过搜索，但得到了不同的答案，我知道值不是空的，因为我在崩溃前将它打印到屏幕上，我对android/java场景还是很陌生，不熟悉线程错误

我读到的是，这可能是由于线程更新了ui，但找不到确切的问题

Logcat:

06-24 16:13:27.287    9388-9415/com.test E/AndroidRuntime﹕ FATAL EXCEPTION: Thread-5023
Process: com.test, PID: 9388
java.lang.NullPointerException
        at com.test.entities.MucOptions.processPacket(MucOptions.java:131)
        at com.test.parser.PresenceParser.parseConferencePresence(PresenceParser.java:35)
        at com.test.services.XmppConnectionService$5.onPresencePacketReceived(XmppConnectionService.java:275)
        at com.test.xmpp.XmppConnection.processPresence(XmppConnection.java:414)
        at com.test.xmpp.XmppConnection.processStream(XmppConnection.java:303)
        at com.test.xmpp.XmppConnection.processStream(XmppConnection.java:244)
        at com.test.xmpp.XmppConnection.switchOverToTls(XmppConnection.java:516)
        at com.test.xmpp.XmppConnection.processStream(XmppConnection.java:236)
        at com.test.xmpp.XmppConnection.connect(XmppConnection.java:175)
        at com.test.xmpp.XmppConnection.run(XmppConnection.java:219)
        at java.lang.Thread.run(Thread.java:841)

public void processPacket(PresencePacket packet, PgpEngine pgp) {


    String[] fromParts = packet.getFrom().split("/");
    if (fromParts.length>=2) {
        String name = fromParts[1];



        Log.i("MUC packet", packet.toString()+"");
        String type = packet.getAttribute("type");
        Element item;
        if (type==null) {
            User user = new User();

            item = packet.findChild("x","http://jabber.org/protocol/muc#user").findChild("item");
            user.setName(name);
            user.setAffiliation(item.getAttribute("affiliation"));
            user.setRole(item.getAttribute("role"));
            user.setName(name);
            if (name.equals(getNick())) {
                this.isOnline = true;
                this.error = 0;
                self = user;
            } else {
                addUser(user);
            }
            if (pgp != null) {
                Element x = packet.findChild("x",
                        "jabber:x:signed");
                if (x != null) {
                    Element status = packet.findChild("status");
                    String msg;
                    if (status != null) {
                        msg = status.getContent();
                    } else {
                        msg = "";
                    }
                    user.setPgpKeyId(pgp.fetchKeyId(account,msg, x.getContent()));
                }
            }
        } else if (type.equals("unavailable")) {
            if (name.equals(getNick())) {
                item = packet.findChild("x","http://jabber.org/protocol/muc#user").findChild("item");
                String nick = item.getAttribute("nick");
                if (nick!=null) {
                    aboutToRename = false;
                    if (renameListener!=null) {
                        renameListener.onRename(true);
                    }
                    this.setNick(nick);
                }
            }
            deleteUser(packet.getAttribute("from").split("/")[1]);
        } else if (type.equals("error")) {
            Element error = packet.findChild("error");
            if (error.hasChild("conflict")) {
                if (aboutToRename) {
                    if (renameListener!=null) {
                        renameListener.onRename(false);
                    }
                    aboutToRename = false;
                } else {
                    this.error  = ERROR_NICK_IN_USE;
                }
            }
        }
    }
}

粘液选项：131

item = packet.findChild("x","http://jabber.org/protocol/muc#user").findChild("item");

完整的MucOptions.java:

06-24 16:13:27.287    9388-9415/com.test E/AndroidRuntime﹕ FATAL EXCEPTION: Thread-5023
Process: com.test, PID: 9388
java.lang.NullPointerException
        at com.test.entities.MucOptions.processPacket(MucOptions.java:131)
        at com.test.parser.PresenceParser.parseConferencePresence(PresenceParser.java:35)
        at com.test.services.XmppConnectionService$5.onPresencePacketReceived(XmppConnectionService.java:275)
        at com.test.xmpp.XmppConnection.processPresence(XmppConnection.java:414)
        at com.test.xmpp.XmppConnection.processStream(XmppConnection.java:303)
        at com.test.xmpp.XmppConnection.processStream(XmppConnection.java:244)
        at com.test.xmpp.XmppConnection.switchOverToTls(XmppConnection.java:516)
        at com.test.xmpp.XmppConnection.processStream(XmppConnection.java:236)
        at com.test.xmpp.XmppConnection.connect(XmppConnection.java:175)
        at com.test.xmpp.XmppConnection.run(XmppConnection.java:219)
        at java.lang.Thread.run(Thread.java:841)

public void processPacket(PresencePacket packet, PgpEngine pgp) {


    String[] fromParts = packet.getFrom().split("/");
    if (fromParts.length>=2) {
        String name = fromParts[1];



        Log.i("MUC packet", packet.toString()+"");
        String type = packet.getAttribute("type");
        Element item;
        if (type==null) {
            User user = new User();

            item = packet.findChild("x","http://jabber.org/protocol/muc#user").findChild("item");
            user.setName(name);
            user.setAffiliation(item.getAttribute("affiliation"));
            user.setRole(item.getAttribute("role"));
            user.setName(name);
            if (name.equals(getNick())) {
                this.isOnline = true;
                this.error = 0;
                self = user;
            } else {
                addUser(user);
            }
            if (pgp != null) {
                Element x = packet.findChild("x",
                        "jabber:x:signed");
                if (x != null) {
                    Element status = packet.findChild("status");
                    String msg;
                    if (status != null) {
                        msg = status.getContent();
                    } else {
                        msg = "";
                    }
                    user.setPgpKeyId(pgp.fetchKeyId(account,msg, x.getContent()));
                }
            }
        } else if (type.equals("unavailable")) {
            if (name.equals(getNick())) {
                item = packet.findChild("x","http://jabber.org/protocol/muc#user").findChild("item");
                String nick = item.getAttribute("nick");
                if (nick!=null) {
                    aboutToRename = false;
                    if (renameListener!=null) {
                        renameListener.onRename(true);
                    }
                    this.setNick(nick);
                }
            }
            deleteUser(packet.getAttribute("from").split("/")[1]);
        } else if (type.equals("error")) {
            Element error = packet.findChild("error");
            if (error.hasChild("conflict")) {
                if (aboutToRename) {
                    if (renameListener!=null) {
                        renameListener.onRename(false);
                    }
                    aboutToRename = false;
                } else {
                    this.error  = ERROR_NICK_IN_USE;
                }
            }
        }
    }
}

---

似乎

muoptions

变量是

null

。如果

item=packet.findChild（“x”），请在对其调用方法之前对其进行初始化http://jabber.org/protocol/muc#userfindChild（“项目”）

是您的第131行，然后是

packet

或

packet.findChild（“x”http://jabber.org/protocol/muc#user“

为

null

请使用以下内容进行检查：

if (packet == null) {
    throw new NullPointerException("packet is null")
} else if (packet.findChild("x","http://jabber.org/protocol/muc#user") == null) {
    throw new NullPointerException("packet.findChild(\"x\",\"http://jabber.org/protocol/muc#user\") is null")
}
item = packet.findChild("x","http://jabber.org/protocol/muc#user").findChild("item");

---

检查第131行，确保该行上的所有变量均为非空。到目前为止，其中一个（或多个）为空。非常感谢，似乎是由于muc#user不在字符串中而导致的子项为空，我现在已修复该问题，并学会了一种新的疑难解答方法。发生错误时，链式调用可能会令人困惑。：）