ArrayList 突然变为 null 之前不为 null

Question

我有一个 LocationMapActivity，它使用 google map v2 来显示人员的位置（根据人员 ID 从数据库中获取位置）。我使用 异步任务 从数据库中获取位置并在地图上添加标记和路线。

我在两种情况下重新使用 LocationMapActivity（根据人员 ID 显示标记/路线）：

1. 单击 Show all people om map Button-LocationMapActivity 显示描绘每个人的标记。如果单击该标记，则通过再次向 LocationMapActivity 发送一个 Intent 到 LocationMapActivity 来显示特定人员的路线，其中人员 ID 为 put extra。

2. 单击幻灯片放映地图按钮 - LocationMapActivity 首先显示描绘所有人的所有标记。然后在 10 秒后重新渲染地图并显示每个人的路线（以 10 秒的间隔逐一显示）。请参阅我的代码的已接受答案：How to place Multiple MapViews v1 inside a ViewFlipper。

问题： 在场景 1 中一切正常。但在场景 2 中，ArraryList latLngArrlist 损失值 突然！。我已经调试了数组列表永远不会设置为空的代码 它随机变为空。这些 arrayList 是私有的，但不是本地的 变量。

注意：：在渲染下一个地图视图之前，我使用了一个重置​​函数来清除所有的数组列表和非局部变量。

我的代码很长，所以我只在下面发布相关的代码：

LocationMapActivity

        public class LocationMapActivity extends Activity implements OnClickListener,
                OnMarkerClickListener {


            private ArrayList<String> latLngCheckinTimeList = null;//
            private ArrayList<String> addressList = null;//
            private  ArrayList<LatLng> latLngArrList = new ArrayList<LatLng>();//
            private ArrayList<Long> checkinTimeArrList = new ArrayList<Long>();//
            private String selectedFieldOfficerId;
            private GoogleMap googleMap;
            private List<List<HashMap<String, String>>> route = null;
            private HashMap<Marker, String> markerHmap = new HashMap<Marker, String>();//


            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.map_activity_screen);
                context = this;
        //person ID according to which will be displayed
                selectedFieldOfficerId = getIntent().getStringExtra(
                        AllConstants.FOIdKey);
                        latLngCheckinTimeList = new ArrayList<String>();

                //my code 

                 googleMap = ((MapFragment) getFragmentManager().findFragmentById(
                        R.id.mapView)).getMap();

                    mapTask = new MapTask(context, selectedFieldOfficerId, this);
                    mapTask.execute();// async task for url of route

                }

                googleMap.setOnMarkerClickListener(this);

    }    


}

MapTask 异步任务

@Override
        protected Void doInBackground(Void... params) {

            helper = new EmployeeHelper(getApplicationContext());

            if (!fieldOfficerId.equals(AllConstants.ShowAllFOInMap)
                    && !fieldOfficerId.equals(AllConstants.ShowAllFOInMapSlide)) {
                // map for specific fo
                showSpecificFoMap(fieldOfficerId);
            } else if (fieldOfficerId.equals(AllConstants.ShowAllFOInMap)) {
                // show all emp in map
                showAllFoOnMap((AllConstants.ShowAllFOInMap));
            } else if (fieldOfficerId.equals(AllConstants.ShowAllFOInMapSlide)) {
                // show slide show 
                                //PROBLEM HERE
                Log.i("map", "in slide show if ");
                ArrayList<String> foIdList = new ArrayList<String>();
                Boolean condition = true;
                while (condition && !isFinishActivity) {
                    // runs only once
                    Log.i("map", "in slide show if WHILE");
                    mapScreenshotsNo = 1;
                    try {
                        foIdList = showAllFoOnMap((AllConstants.ShowAllFOInMapSlide));//ARRAYLIST BECOMES NULL IN THIS FUNCTION
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    runOnUiThread(new Runnable() {
                        public void run() {
                            if (progressDialog != null
                                    && progressDialog.isShowing()
                                    && !isFinishActivity)
                                progressDialog.dismiss();
                        }
                    });
                    try {
                        util.haveASleep(slideShowInterval);
                    } catch (Exception e) {

                        e.printStackTrace();
                    }


                    resetVariables();
                    mapScreenshotsNo++;
                    if (foIdList != null) {
                        try {
                            mapScreenshotsNo = showEachFOMap(foIdList,
                                    mapScreenshotsNo);
                        } catch (Exception e) {

                            e.printStackTrace();
                        }
                        resetVariables();
                    }

                    condition = false;

                }
                if (mapTask != null)
                    mapTask.cancel(true);
                // mapActivity.finish();
            }
            return null;
        }

我了解 Arraylist 正在失去价值。但我不知道如何将 ArrayList 类型保存在持久内存中，因为它不是原始类型。几天以来我一直在努力解决这个问题。

EDIT ：ArrayList 突然变为空，任何设置模式。有时代码运行良好，有时它在arraylists 处给出空指针。通常空指针是由ArrayList latLngArrList引起的

请帮忙！！！

谢谢。

Answer 1

尝试更改这些变量值初始化：

private ArrayList<String> latLngCheckinTimeList = null;

只是

private ArrayList<String> latLngCheckinTimeList;

并将变量创建移至 onCreate：

private  ArrayList<LatLng> latLngArrList = new ArrayList<LatLng>();//

onCreate..

latLngArrList = new ArrayList<LatLng>();

Answer 2

这是datacontroller类，它是单例类的意思是只有单个对象或单个实例的类，我们称之为单例类。

     public class DataController {

            private static DataController ref;

            public static DataController getInstance()
            {
                if(ref==null)
                    ref = new DataController();

                return ref;
            }

            public void deleteInstance()
            {
                ref=null;
            }

    //here we can declare any type of data either it is primitive type or derived type data like this 

    public ArrayList<CommanWrapperForListing> arraylist_wrapper_datacntrlr = new ArrayList<CommanWrapperForListing>();

        public boolean iswifi = true; 

        public HashMap<String, ArrayList<CommanWrapperForListing>>caching = new HashMap<String,    ArrayList<CommanWrapperForListing>>();
        public HashMap<String, HashMap<String, ArrayList<CommanWrapperForListing>>>caching_machine = new HashMap<String, HashMap<String, ArrayList<CommanWrapperForListing>>>(); 


// now the place where u receive or fill arraylist then use this like 

DataController datacntrl; // global declare this 

 public ArrayList<CommanWrapperForListing> arraylist_wrapper_local = new ArrayList<CommanWrapperForListing>();//global same as datacotrller have 

datacntrl = DataController.getInstance(); // in oncreate()

//then fill your arraylist which is same as u declare in datacontroller getting my point means both are same type of arraylist 

//then just put this data type into the datacontroller class like this 

datacntrl.arraylist_wrapper_datacntrlr .add(new CommanWrapperForListing(new File(path).getName(), path, "Audio",false,color_string));

//or you can also do this 
controller.arraylist_wrapper_datacntrlr = arraylist_wrapper_local ;//once you fill this local arraylist then put it into datacontroller class varible 

//now just use this datacontroller arraylist it will never loss untill n unless u not delete it into stack 

 //use like 

//datacntrl.arraylist_wrapper_datacntrlr ; as we use static member of any class 

亲爱的，我尽力描述这个好运：)