使用ArrayLists时出现奇怪的NPE行为

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我有一个名为public static ArrayList<Integer>的3个hp,att & def数组列表，分别名为GlobalDataHolder.java。当我尝试从另一个名为ArrayLists的类中的addSelectedCardToGlobalUserBox方法中向那些MainScreenFragment.java添加一个Integer值时，我得到一个NPE，表明hp ArrayList为null，从而阻止我向其添加值。奇怪的是，这种异常只发生在我在物理设备而不是模拟器上运行应用程序时。有任何想法吗？

的ArrayList：

    // Holds each card's hp stats
public static ArrayList<Integer> hp = new ArrayList<>();

// Holds each card's att stats
public static ArrayList<Integer> att = new ArrayList<>();

// Holds each card's def stats
public static ArrayList<Integer> def = new ArrayList<>();

addSelectedCardToGlobalUserBox（）方法：

    /**
 * Add the selected card's icon to the Global User Box
 * @param position Holds the selected card's position.
 * This is used to define where the icon should be placed in the grid &
 * which icon from the DataBase was selected
 */
private void addSelectedCardToGlobalUserBox(int position) {
    GlobalDataHolder.dataHolder.add(ImageAdapter.mThumbIds[position]);
    GlobalDataHolder.cardArts.add(CardInfoDatabase.cardArts[position]);
    GlobalDataHolder.cardNameAndDescription.add(CardInfoDatabase.cardNameAndDescription[position]);
    GlobalDataHolder.leaderSkills.add(CardInfoDatabase.leaderSkills[position]);
    GlobalDataHolder.superAttacksName.add(CardInfoDatabase.superAttacksName[position]);
    GlobalDataHolder.superAttacksDesc.add(CardInfoDatabase.superAttacksDesc[position]);
    GlobalDataHolder.passiveSkillsName.add(CardInfoDatabase.passiveSkillsName[position]);
    GlobalDataHolder.passiveSkillsDesc.add(CardInfoDatabase.passiveSkillsDesc[position]);
    GlobalDataHolder.hp.add(CardInfoDatabase.hp[position]);
    GlobalDataHolder.att.add(CardInfoDatabase.att[position]);
    GlobalDataHolder.def.add(CardInfoDatabase.def[position]);
}

MainScrenFragment.java类供参考：

public class MainScreenFragment extends Fragment {

// Main Grid View
GridView gridView;

public MainScreenFragment() {
    // Required empty public constructor
}

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

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

    gridView = view.findViewById(R.id.gridViewLayout);
    gridView.setAdapter(new ImageAdapter(getContext())); // used to set the contents of the GridView-in this case images-
    registerForContextMenu(gridView);

    // When an item from the GridView gets clicked
    gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            // Create a new Intent...
            Intent intent = new Intent(getContext(),CardViewActivity.class);
            intent.putExtra("Card Index",position);
            intent.putExtra("GLB_CARD_INDEX", -1);
            intent.putExtra("SCREEN_WIDTH",1080);
            startActivity(intent);
        }
    });
    return view;
}

// Create a Context Menu when an item in the GridView is long-pressed
@Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
    super.onCreateContextMenu(menu, v, menuInfo);
    menu.setHeaderTitle("Card Options");
    //AdapterView.AdapterContextMenuInfo cmi = (AdapterView.AdapterContextMenuInfo) menuInfo;
    menu.add(1,v.getId(),0, "Add Card to GLB");
    menu.add(2,v.getId(),0,"Add Card to JP");
}

// When an item in the context menu gets selected, call a method
@Override
public boolean onContextItemSelected(MenuItem item) {

    // Get some extra info about the contextMenu
    AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();

    int position = info.position; // clicked view's position

    if(item.getTitle().equals("Add Card to GLB")) {
        addCardMessage("Card added to GLB");
        addSelectedCardToGlobalUserBox(position);
    } else if (item.getTitle().equals("Add Card to JP")) {
        addCardMessage("Card added to JP");
        addSelectedCardToJPUserBox(position);
    } else
    {
        return false;
    }
    return false;
}

/**
 * Creates a snackbar message, telling the user which card was added to which box
 * @param text Defines into which User Box the card was added
 */
private void addCardMessage( String text) {
      final Snackbar snackbar = Snackbar.make(gridView, text ,Snackbar.LENGTH_LONG);

      snackbar.setAction("Dismiss", new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            snackbar.dismiss();
        }
    });
    snackbar.setActionTextColor(Color.MAGENTA);
    snackbar.show();
}

/**
 * Add the selected card's icon to the Global User Box
 * @param position Holds the selected card's position.
 * This is used to define where the icon should be placed in the grid &
 * which icon from the DataBase was selected
 */
private void addSelectedCardToGlobalUserBox(int position) {
    GlobalDataHolder.dataHolder.add(ImageAdapter.mThumbIds[position]);
    GlobalDataHolder.cardArts.add(CardInfoDatabase.cardArts[position]);
    GlobalDataHolder.cardNameAndDescription.add(CardInfoDatabase.cardNameAndDescription[position]);
    GlobalDataHolder.leaderSkills.add(CardInfoDatabase.leaderSkills[position]);
    GlobalDataHolder.superAttacksName.add(CardInfoDatabase.superAttacksName[position]);
    GlobalDataHolder.superAttacksDesc.add(CardInfoDatabase.superAttacksDesc[position]);
    GlobalDataHolder.passiveSkillsName.add(CardInfoDatabase.passiveSkillsName[position]);
    GlobalDataHolder.passiveSkillsDesc.add(CardInfoDatabase.passiveSkillsDesc[position]);
    GlobalDataHolder.hp.add(CardInfoDatabase.hp[position]);
    GlobalDataHolder.att.add(CardInfoDatabase.att[position]);
    GlobalDataHolder.def.add(CardInfoDatabase.def[position]);
}

/**
 * Add the selected card's icon to the JP User Box
 * @param position Holds the selected card's position.
 * This is used to define where the icon should be placed in the grid &
 * which icon from the DataBase was selected
 */
private void addSelectedCardToJPUserBox(int position) {
    JPDataHolder.dataHolder.add(ImageAdapter.mThumbIds[position]);
    JPDataHolder.cardArts.add(CardInfoDatabase.cardArts[position]);
    JPDataHolder.cardNameAndDescription.add(CardInfoDatabase.cardNameAndDescription[position]);
    JPDataHolder.leaderSkills.add(CardInfoDatabase.leaderSkills[position]);
    JPDataHolder.superAttacksName.add(CardInfoDatabase.superAttacksName[position]);
    JPDataHolder.superAttacksDesc.add(CardInfoDatabase.superAttacksDesc[position]);
    JPDataHolder.passiveSkillsName.add(CardInfoDatabase.passiveSkillsName[position]);
    JPDataHolder.passiveSkillsDesc.add(CardInfoDatabase.passiveSkillsDesc[position]);
    JPDataHolder.hp.add(CardInfoDatabase.hp[position]);
    JPDataHolder.att.add(CardInfoDatabase.att[position]);
    JPDataHolder.def.add(CardInfoDatabase.def[position]);
}

}

名称：

01-01 16：05：51.421 22357-22357 / com.dcv.spdesigns.dokkancards E / androidRuntime：FATAL EXCEPTION：main进程：com.dcv.spdesigns.dokkancards，PID：22357 java.lang.NullPointerException：尝试调用虚拟com.dcv.spdesigns上com.dcv.spdesigns.dokkancards.ui.MainScreenFragment.addSelectedCardToGlobalUserBox（MainScreenFragment.java:122）中空对象引用的方法'boolean java.util.ArrayList.add（java.lang.Object）' Android.support.v4.app.FragmentManagerImpl.dispatchContextItemSelected（FragmentManager.java）上的android.support.v4.app.Fragment.performContextItemSelected（Fragment.java:2502）中的.dokkancards.ui.MainScreenFragment.onContextItemSelected（MainScreenFragment.java:79） ：android.support.v4.app.FragmentController.dispatchContextItemSelected（FragmentController.java：357）在android.support.v7.app的android.support.v4.app.FragmentActivity.onMenuItemSelected（FragmentActivity.java:377）的android.support.v4.app.FragmentController.dispatchContextItemSelected（339）。 android.support上的AppCompatActivity.onMenuItemSelected（AppCompatActivity.java:195）。位于com.android.internal.policy.PhoneWindow $ PhoneWindowMenuCallback.onMenuItemSelected（PhoneWindow。）的android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected（WindowCallbackWrapper.java:108）的v7.view.WindowCallbackWrapper.onMenuItemSelected（WindowCallbackWrapper.java:108）。 java：4020）com.android.internal.view.menu.MenuBuilder.dispatchMenuItemSelected（MenuBuilder.java:761）位于com.android的com.android.internal.view.menu.MenuItemImpl.invoke（MenuItemImpl.java:157） .internal.view.menu.MenuBuilder.performItemAction（MenuBuilder.java:904）位于com.android.internal.view.menu.MenuPopup的com.android.internal.view.menu.MenuBuilder.performItemAction（MenuBuilder.java:894） .onItemClick（MenuPopup.java:128）位于android.widget.Ab上的android.widget.AdapterView.performItemClick（AdapterView.java:339），android.widget.AbsListView，$。 AbsListView.java:4184）在android.os.Handler.h的android.widget.AbsListView $ 13.run（AbsListView.java:6754） andleCallback（Handler.java:751）在Android.os.Handler.dispatchMessage（Handler.java:95）android.app.Looper.loop（Looper.java:154）android.app.ActivityThread.main（ActivityThread.java） ：6776）位于com.android.internal.os.ZygoteInit.main的com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1520）的java.lang.reflect.Method.invoke（Native Method） （ZygoteInit.java:1410）

答案

在代码中的某处，您必须分配这些变量null。尝试制作变量final并检查null的分配位置（编译失败将指示您指定null的位置）。

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