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我正在使用 moveTaskToBack 将我的应用程序置于后台。应用程序在 OS 2.2 中运行良好，但是当我在 OS 2.3.6 中测试相同的应用程序时，我遇到了一些奇怪的问题。
如果我将应用程序置于后台，然后再次置于前台，则互联网连接正常，但当应用程序处于前台时，如果我断开互联网连接，将应用程序置于后台，当我再次返回应用程序时，意味着应用程序进入前台我的应用程序调用 onCreate() 并且应用程序崩溃的时间。

代码：

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

// ////////////////////////////////////////////////////////////

Log.d("BuddyList ", "OnCreate");

txtIsConnected = (TextView) findViewById(R.id.isConnected);
txtIsConnected.setText("Online");
txtIsConnected.setTextColor(Color.GREEN);

listener = new PacketListener() {
public void processPacket(Packet packet) {

ActivityManager am = (ActivityManager) SnapApp.getInstance()
.getSystemService(ACTIVITY_SERVICE);
List<ActivityManager.RunningTaskInfo> taskInfo = am
.getRunningTasks(1);
ComponentName componentInfo = taskInfo.get(0).topActivity;

String className = componentInfo.getClassName();

if (packet instanceof Message) {
final Message message = (Message) packet;

if (className
.equalsIgnoreCase("com.snapwork.xmppchatapp.ChatActivity")) {
if (ChatActivity.instance.to.contains(StringUtils
.parseBareAddress(message.getFrom()))) {
runOnUiThread(new Runnable() {
@Override
public void run() {
// TODO Auto-generated method stub
ChatActivity.instance.name(
message.getBody(),
ChatActivity.instance.to);
}
});

} else {
if (XMPPClient.notificationSenders.size() > 0
&& XMPPClient.notificationSenders
.contains(StringUtils
.parseBareAddress(message
.getFrom()))) {
NOTIFICATION_ID++;
}

XMPPClient.notificationMessages.add(message
.getBody());
XMPPClient.notificationSenders.add(StringUtils
.parseBareAddress(message.getFrom()));

runOnUiThread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
Notifications.addNotification(
message.getFrom(),
message.getBody());
}
});

}
} else if (className
.equalsIgnoreCase("com.snapwork.xmppchatapp.BuddyList")) {
XMPPClient.OfflineMessages.add(message.getBody());
XMPPClient.OfflineSenders.add(StringUtils
.parseBareAddress(message.getFrom()));

runOnUiThread(new Runnable() {

@Override
public void run() {
mAdapter = new DataAdapter(BuddyList.this,
R.layout.multi_line_list_item, datalist);
listMessages.setAdapter(mAdapter);
mAdapter.notifyDataSetChanged();
}
});

}

else {
// System.out.println("While some where !!!");

XMPPClient.notificationMessages.add(message.getBody());
XMPPClient.notificationSenders.add(StringUtils
.parseBareAddress(message.getFrom()));

runOnUiThread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
Notifications.addNotification(
message.getFrom(), message.getBody());
}
});
}

} else if (packet instanceof Presence) {
// System.out.println("u have a frnd requ........ !!!");
}

}
};

// ////////////////////////////////////////////////////////////

PacketFilter filter = new MessageTypeFilter(Message.Type.chat);
XMPPClient.connection.addPacketListener(listener, filter);

buddyList = getIntent().getStringArrayListExtra("buddyList");
buddyStatus = getIntent().getStringArrayListExtra("buddystatus");

filteredList = getIntent().getStringArrayListExtra("buddyList");

filteredStat = getIntent().getStringArrayListExtra("buddystatus");
datalist = buddyList.toArray(new String[buddyList.size()]);
Statlist = buddyStatus.toArray(new String[buddyStatus.size()]);
recipient = (EditText) findViewById(R.id.recipient);
imgFindAdd = (ImageView) findViewById(R.id.findAddAccount);

imgFindAdd.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub

Intent i = new Intent(BuddyList.this, FindAndAdd.class);
i.putStringArrayListExtra("buddyList", buddyList);
i.putStringArrayListExtra("buddystatus", buddyStatus);
// startActivity(i);

startActivity(i);

}
});

for (int i = 0; i < datalist.length; i++) {
// Log.d("datalist : ", "" + datalist[i]);
}
listMessages = (ListView) findViewById(R.id.listMessages);
// setListAdapter();

mAdapter = new DataAdapter(BuddyList.this,
R.layout.multi_line_list_item, datalist);
listMessages.setAdapter(mAdapter);
mAdapter.notifyDataSetChanged();
listMessages.setTextFilterEnabled(true);
listMessages.setOnItemClickListener(new OnItemClickListener() {

@Override
public void onItemClick(AdapterView<?> arg0, View v, int position,
long id) {

Intent intent = new Intent(BuddyList.this, ChatActivity.class);
Bundle b = new Bundle();
b.putString("to", filteredList.get(position));

intent.putExtras(b);
intent.putExtra("ustatus", Statlist[position]);

intent.putExtra("from", "BuddyList");
startActivity(intent);

}
});

/**
* Enabling Search Filter
* */
recipient.addTextChangedListener(new TextWatcher() {

@Override
public void onTextChanged(CharSequence cs, int arg1, int arg2,
int arg3) {
// When user changed the Text
BuddyList.this.mAdapter.getFilter().filter(cs);

}

@Override
public void beforeTextChanged(CharSequence arg0, int arg1,
int arg2, int arg3) {
// TODO Auto-generated method stub

}

@Override
public void afterTextChanged(Editable arg0) {
// TODO Auto-generated method stub
}
});

packetListener = new PacketListener() {

@Override
public void processPacket(Packet packet) {

final Presence presence = (Presence) packet;

if (presence.getType() == Type.available
|| presence.getType() == Type.unavailable) {
System.out.println("Finally Changing");
refresh();
}

ActivityManager am = (ActivityManager) SnapApp.getInstance()
.getSystemService(ACTIVITY_SERVICE);

List<ActivityManager.RunningTaskInfo> taskInfo = am
.getRunningTasks(1);
ComponentName componentInfo = taskInfo.get(0).topActivity;

String className = componentInfo.getClassName();

if (className
.equalsIgnoreCase("com.snapwork.xmppchatapp.BuddyList")) {

if (presence.getType() == Type.subscribe) {

XMPPClient.OfflineFrndReq
.add(presence.getType().name());
XMPPClient.OfflineFrndReqSender.add(presence.getFrom());
FriendRequestNotification.addNotification(
presence.getFrom(), "abcd");

} else if (presence.getType() == Type.unsubscribed) {
runOnUiThread(new Runnable() {

@Override
public void run() {
ShowToast1();
}
});

} else if (presence.getType() == Type.subscribed) {

Presence subscribed = new Presence(
Presence.Type.subscribed);
subscribed.setTo(StringUtils.parseBareAddress(presence
.getFrom()));
XMPPClient.connection.sendPacket(subscribed);

runOnUiThread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
if (XMPPClient.flag)
new ShowDialogAsyncTask().execute();
else
ShowToast();
}
});

}

}

}
};

XMPPClient.connection.addPacketListener(packetListener,
new PacketTypeFilter(Presence.class));

Button btnSwitch = (Button) findViewById(R.id.switchaccount);

btnSwitch.setOnClickListener(new OnClickListener() {

@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent i = new Intent(BuddyList.this, Accounts.class);
startActivity(i);
}
});

}

日志猫：
04-08 11:33:53.585: E/AndroidRuntime(29175): FATAL EXCEPTION: main 04-08 11:33:53.585: E/AndroidRuntime(29175): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.snapwork.xmppchatapp/com.snapwork.xmppchatapp.BuddyList}: java.lang.NullPointerException 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.os.Handler.dispatchMessage(Handler.java:99) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.os.Looper.loop(Looper.java:130) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.app.ActivityThread.main(ActivityThread.java:3687) 04-08 11:33:53.585: E/AndroidRuntime(29175): at java.lang.reflect.Method.invokeNative(Native Method) 04-08 11:33:53.585: E/AndroidRuntime(29175): at java.lang.reflect.Method.invoke(Method.java:507) 04-08 11:33:53.585: E/AndroidRuntime(29175): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 04-08 11:33:53.585: E/AndroidRuntime(29175): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 04-08 11:33:53.585: E/AndroidRuntime(29175): at dalvik.system.NativeStart.main(Native Method) 04-08 11:33:53.585: E/AndroidRuntime(29175): Caused by: java.lang.NullPointerException 04-08 11:33:53.585: E/AndroidRuntime(29175): at com.snapwork.xmppchatapp.BuddyList.onCreate(BuddyList.java:266) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 04-08 11:33:53.585: E/AndroidRuntime(29175): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 04-08 11:33:53.585: E/AndroidRuntime(29175): ... 11 more 04-08 11:33:53.593: E/liblog(1514): failed to call dumpstate 04-08 11:33:53.593: E/(1514): Dumpstate > /data/log/dumpstate_app_error

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