java - fragment 内的addView()抛出NullPointerException

我正在使用具有MyAdapter的Fragment Activity进行Android项目：

public static class MyAdapter extends FragmentPagerAdapter {
        public MyAdapter(FragmentManager fragmentManager) {
            super(fragmentManager);
        }

        @Override
        public int getCount() {
            return ITEMS;
        }

        @Override
        public Fragment getItem(int position) {
            switch (position) {
            case 0: // Fragment # 0 - Pokazuje listę
                return ImageFragment.init(position);
                //return TruitonListFragment.init(position);
            case 1: // Fragment # 1 - Pokazuje wybór
                return ImageFragment.init(position);
            default:
                return ImageFragment.init(position);
            }
        }
    }

现在，我有了扩展Fragment的ImageFragment类。我正在尝试将ImageFragment内的addView（）添加到布局中的元素上，并且出现了NullPointerException。它可以在Activity中使用，但在Fragment中不能使用。可以解决该问题，这到底是怎么回事？

public class ImageFragment extends Fragment implements OnClickListener {

    int fragVal;

    public static ImageFragment init(int val) {
        ImageFragment truitonFrag = new ImageFragment();
        // Supply val input as an argument.
        Bundle args = new Bundle();
        args.putInt("val", val);
        truitonFrag.setArguments(args);
        return truitonFrag;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        InitializeDatabase(); // Wczytanie zasobów

        fragVal = getArguments() != null ? getArguments().getInt("val") : 1;

        //
        AddonsList = new ArrayList<myAddons>();

        //
        Parent = new ArrayList<Long>();
        Parent.add((long) 0);
        GenerateNodeTree((long) 0); // Ustawienie fragmentu na początek
    }

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

        View layoutView = inflater.inflate(R.layout.fragment_pager_list,
                container, false);
        linearLayout = new LinearLayout(getActivity());
        linearLayout = (LinearLayout) layoutView.findViewById(R.id.Groups);
        linearLayout = new LinearLayout(getActivity());
        GoTop = (Button) layoutView.findViewById(R.id.Button02);
        GoHome = (Button) layoutView.findViewById(R.id.Button01);

        return layoutView;
    }

    private void GenerateNodeTree(Long TreeNode) {
        try {
            currentProductList = new ArrayList<Products>();
            ClearView();

            for(ProductGroups grupa : myGroupList) {
                Log.i("mm",grupa.getNazwa());

                LinearLayout row = new LinearLayout(getActivity());
                row.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
                if(grupa.getPARENTID() == TreeNode & grupa.getPOSPRODID() == 0) { // Przyciski kategorii

                    ImageButton imgTag = new ImageButton(getActivity());
                    Button btnTag = new Button(getActivity());

                    int k = R.drawable.icon_empt;
                    imgTag.setImageResource(k);

                    btnTag.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
                    btnTag.setText(grupa.getNazwa());
                    btnTag.setId((int) grupa.getPOSPRODGRPID());
                    btnTag.setOnClickListener(this);

                    row.addView(imgTag);
                    row.addView(btnTag);
                    linearLayout.addView(row); // HERE NULL POINTER APPEARS
                }

            }
        }
        catch(Exception exc)
        {
            //Print.StandardToast(getActivity(), exc.getStackTrace().toString());
        }
        // Koniec generowania widoku
    }

}

最佳答案

您的片段类中似乎没有一个linearLayout字段（是否省略了代码？）。无论如何，您似乎在linearLayout回调中初始化了onCreateView()字段。问题是您试图在onCreate()方法中（通过GenerateNodeTree()调用）使用它，该方法在onCreateView()之前被调用（因此linearLayout那时不会被初始化）。因此，将GenerateNodeTree((long) 0);调用移至onCreateView()或onActivityCreated()之后调用的onCreateView()中。

关于java - fragment 内的addView()抛出NullPointerException，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/17169077/