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从数据库中提取位置）。我使用异步任务< / strong>从数据库中获取位置并在地图上添加标记和路径。

我在两种情况下使用LocationMapActivity（根据人物ID显示标记/路线）：

点击显示所有人的地图Button-LocationMapActivity显示描绘每个人的标记。如果单击标记，则再次向LocationMapActivity发送意图并将人员ID作为额外发送，显示特定人的路线。 / p>

点击幻灯片放映地图按钮 - 位置地图活动首先显示描绘所有人的所有标记。然后在10秒之后，它重新呈现每个人的地图和显示路线（一个接一个，间隔10秒）。请参阅我的代码的已接受答案：How to place Multiple MapViews v1 inside a ViewFlipper。

问题：在方案1中，一切都运行良好。但在方案2中，ArraryList latLngArrlist损失值突然！我调试了代码，数组列表永远不会设置为null 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，我使用重置功能清除所有的arraylists和非局部变量。

我的代码非常冗长，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; }

我理解Arraylists正在失去价值。但我不知道如何在持久性内存中保存ArrayList类型，因为它不是主要类型。几天之后我就一直在努力解决这个问题。

编辑：使用任何设置模式，ArrayList突然变为空。有时，代码在arraylists中给出空指针时运行正常。通常，空指针由ArrayList latLngArrList
引起
请帮忙!!!

感谢。

Answer 1

尝试更改这些变量值：

private ArrayList<String> latLngCheckinTimeList = null;

到

private ArrayList<String> latLngCheckinTimeList;

将变量创建移动到onCreate：

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

的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

我尽力描述这件好运，亲爱的：）

ArrayList突然变为null，之前不为null

2 个答案: