尝试将 linkedlist 传递给 fragment 并对其进行任何操作时，Android 应用程序崩溃

问：

我正在尝试在列表视图中显示这些对象的字段，该列表视图正在工作并且位于片段中。我的问题是我拥有的任何示例都有效，它似乎是针对数组列表而不是链接列表。然后，我将转换为 arraylist 以 puplate listview 或找到一种使用 linkedlist 的方法。

在我的代码中，我创建了一个新的链表，并在mainactivity中填充了对象。我在mainactivity中有一个getter来检索列表。我有一个片段列表视图（在解析数据并填充 linkedlist 后创建）。我正在尝试用这些对象的字段填充列表视图项，但不知道如何做到这一点。我正处于一个阶段，在我尝试对链表做任何事情之前，我无法以任何方式访问它，而不会我的应用程序崩溃。

如下图所示，我正在创建和填充我的链表等，然后在 listviewfragment 中尝试访问它，并最终使用/更改它来填充我的列表视图。请原谅代码的混乱，我一直在尝试多种不同的方法来做到这一点，并且每次启动时崩溃时都会遇到相同的问题，没有错误消息。

据我了解，我正在我的片段中创建一个项目列表，该列表被设置为主活动返回的列表，并且我尝试了简单的每个循环来获取描述，但无论我对任何代码段进行什么更改，应用程序都会在启动时立即崩溃，没有任何错误消息。

MainActivity 公共类 MainActivity 扩展 AppCompatActivity 实现 OnClickListener { 私有 TextView rawDataDisplay;

private Button startButton;
private String result = "";
private String url1="http://www.bgs.ac.uk/images/logos/bgs_c_w_227x50.gif";
private String[] items;
Map<String, List<ItemClass>> mylist;
LinkedList <ItemClass> alist = null;
ItemClass[] arrayofitems = null;
List <ItemClass> Testlist = null;
List<ItemClass> list = null;
ItemClass item = null;
private String urlSource="http://quakes.bgs.ac.uk/feeds/MhSeismology.xml";
private IncidentFragment incidentfragment;
private DateRefineFragment daterefinefragment;
private SearchFragment searchfragment;
private ViewFragment viewfragment;
//private LogoFragment logofragment;
private ListviewFragment listviewfragment;
private ListtextviewFragment listtextviewfragment;
private BtntextviewFragment btntextviewfragment;


@Override
protected void onCreate(Bundle savedInstanceState)
{
    LinkedList <ItemClass> alist = null;
    items = new String[50];
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    startProgress();//Parse data and prepare for user selection on startup of app
    // Set up the raw links to the graphical components
    daterefinefragment = new DateRefineFragment();
    searchfragment = new SearchFragment();
    viewfragment = new ViewFragment();
    listviewfragment = new ListviewFragment();
    listtextviewfragment = new ListtextviewFragment();
    btntextviewfragment = new BtntextviewFragment();


    //fragments
    FragmentManager manager1 = getSupportFragmentManager();
    FragmentTransaction transaction1 = manager1.beginTransaction();
    transaction1.replace(R.id.listtextviewFragment, listtextviewfragment);
    transaction1.commit();

    FragmentManager manager2 = getSupportFragmentManager();
    FragmentTransaction transaction2 = manager2.beginTransaction();
    transaction2.replace(R.id.btntextviewFragment, btntextviewfragment);
    transaction2.commit();

    FragmentManager manager3 = getSupportFragmentManager();
    FragmentTransaction transaction3 = manager3.beginTransaction();
    transaction3.replace(R.id.daterefineFragment, daterefinefragment);
    transaction3.commit();

    FragmentManager manager4 = getSupportFragmentManager();
    FragmentTransaction transaction4 = manager4.beginTransaction();
    transaction4.replace(R.id.searchFragment, searchfragment);
    transaction4.commit();

    FragmentManager manager5 = getSupportFragmentManager();
    FragmentTransaction transaction5 = manager5.beginTransaction();
    transaction5.replace(R.id.viewFragment, viewfragment);
    transaction5.commit();

    FragmentManager manager6 = getSupportFragmentManager();
    FragmentTransaction transaction6 = manager6.beginTransaction();
    transaction6.replace(R.id.listviewFragment, listviewfragment);
    transaction6.commit();

    // More Code goes here
}

public void onClick(View aview) //probs dont need this with button fragments
{
    //startProgress();
}

public void startProgress()
{
    // Run network access on a separate thread;
    new Thread(new Task()).start();

} //



// Need separate thread to access the internet resource over network
// Other neater solutions should be adopted in later iterations.
private class Task implements Runnable
{
    @Override
        public void run()
        {

            AccessWeb aw = new AccessWeb();//Create object to make use of class
            result = aw.getResult(urlSource);//Runs code within class to retrieve resulting string of data
            new Thread(new dataparsing()).start();//runs parsing of data on seperate thread
        }

        }

public class dataparsing implements Runnable
{
    @RequiresApi(api = Build.VERSION_CODES.N)
    @Override
    public void run() { //creates new ParseData object and sets alist to returned templist.
        ParseData dp = new ParseData();
        alist = dp.parseData(result);
        //arrayofitems = alist.toArray();
        list = new ArrayList<ItemClass>(alist);
        //Log.d("UI thread", "ARRAYOFITEMS " +  arrayofitems[0].);
         mylist = alist.stream().collect(Collectors.groupingBy(ItemClass::getlocation)); //Set mylist to returned list grouped by location
        Testlist = mylist.get("HIGHLAND");//set test list to list  returned by get with location of passed string ("GWENT")
        item = Testlist.get(1); //set item to object returned in first index of previously returned list (Testlist)
         Log.d("UI thread", "List test = " + list.get(0) + " " + item.getdescription());//prints location of first item in
        // previously returned list
    }
}


public  void loggingMethod()  //Method used for logging information.
{

        Log.d("UI thread", "I am the UI thread");
        //rawDataDisplay.setText(result); doesnt work as its not being run in main thread
        Log.d("UI thread", "first in list printed is " + alist.getFirst() + " and last in list printed is " + alist.getLast());

Log.d（“UI 线程”， “url1 是” + url1）;呜呜呜创建一个新项目来获取这个工人 }

public List<ItemClass> getList() {
    return alist;
}

Listview Fragment 公共类 ListviewFragment 扩展了 Fragment 实现 AdapterView.OnItemClickListener、View.OnClickListener {

@Override
public View onCreateView(
        LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState
)
{


    // Inflate the layout for this fragment
    View v = inflater.inflate(R.layout.frag_listviewfragment, container, false);








    return v;
}

public void onViewCreated(@NonNull View view, Bundle savedInstanceState)
{


    super.onViewCreated(view, savedInstanceState);
    ListView listView = (ListView) view.findViewById(R.id.list);
    listView.setOnItemClickListener((AdapterView.OnItemClickListener) this);

    List<ItemClass> items = ((MainActivity)getActivity()).getList();

    for(ItemClass i : items){
        Log.d("UI thread", "I am the UI thread " + i.getdescription());
    }
    //UserAdapter<ItemClass> adapter = new UserAdapter<ItemClass>(users);



}