java - 布局充气器 nullPointerException

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 3 年前。

社区去年审查了是否重新开放此问题，并将其关闭:

原始关闭原因未解决

我遇到运行时错误。收到此错误消息:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.LayoutInflater.inflate(int, android.view.ViewGroup, boolean)' on a null object reference

工作室指向这一行:

View view= lI.inflate(R.layout.fragment_frag3,container,false);

public class Frag3 extends Fragment {

    ViewPager viewPager;
    CardAdapter2 adapter2;
    List<String> cardWords;
    LayoutInflater lI;

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

        View view= lI.inflate(R.layout.fragment_frag3,container,false);
        viewPager= (ViewPager)view.findViewById(R.id.vp);
        viewPager.setAdapter(adapter2);
        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
        cardWords= new ArrayList<>();
        cardWords.add("x");
        cardWords.add("y");
        cardWords.add("z");

        adapter2= new CardAdapter2(getActivity(),cardWords);

        // Inflate the layout for this fragment
        return view;
    }


}

适配器:

public class CardAdapter2 extends PagerAdapter {
    private Context mContext;
    private List<String> cardWords;
    private LayoutInflater layoutInflater;

    public CardAdapter2(Context mContext, List<String> cardWords) {
        this.mContext = mContext;
        this.cardWords = cardWords;
    }

    @Override
    public int getCount() {
        return cardWords.size();
    }

    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        layoutInflater= LayoutInflater.from(mContext);
        View view= layoutInflater.inflate(R.layout.card_design2,container,false);

        TextView title= view.findViewById(R.id.textView2);
        title.setText(cardWords.get(position));
        container.addView(view,0);

        return super.instantiateItem(container, position);
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        container.removeView((View)object);
    }

    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        return view.equals(object);
    }


}

Answer 1

你定义一个类变量LayoutInflater

LayoutInflater lI;

在 Frag3 类的顶部。然后在 onCreateView 方法中，对未初始化的充气器调用充气。您已经传入了布局充气器，因此您需要进行的更改是

View view= inflater.inflate(R.layout.fragment_frag3,container,false);

只需对传递给您的 LI 调用 inflate