android - fragment 中的 ListView setAdapter，空指针异常

Question

我在 listView 的 setAdapter 遇到了这个空指针异常。 listView 和 Adapter 都是NOT null。

这里有什么问题？

fragment 的OnCreateView

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
        View dataSearch = inflater.inflate(R.layout.fragment_datasearch,container,false);
        itemList = (ListView)dataSearch.findViewById(R.id.searchResults);
//        Item list is not null

            adapter = new SearchAdapter(getActivity(), R.layout.row, item);
//          adapter is not null
            if (!itemList.equals("")){

                itemList.setAdapter(adapter);
                itemList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

                    }
                });}
            else System.out.println("null");

        return dataSearch;
    }

适配器类

public  class SearchAdapter extends ArrayAdapter<FoodItem> {

    ArrayList<Item> item;
    Context context;
    int Resources;
    LayoutInflater vi;


    public SearchAdapter(Context context, int resource, ArrayList<Item> objects) {
        super(context, resource, objects);
        item = objects;
        Resources = resource;
        this.context = context;
            vi = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View row = convertView;
        ViewHolder holder;


        if (convertView == null) {
            convertView = vi.inflate(Resources, null);
            holder = new ViewHolder();
            holder.name = (TextView) convertView.findViewById(R.id.name);
            holder.count = (TextView) convertView.findViewById(R.id.count);
            holder.brand = (TextView) convertView.findViewById(R.id.brand);

            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        holder.populateFrom(item.get(position));
        holder.name.setText(item.get(position).name);
        holder.count.setText(item.get(position).count);
        holder.brand.setText(item.get(position).brand);

        return convertView;
    }

}
class ViewHolder {
    public TextView name = null;
    public TextView count= null;
    public TextView brand=null;

    void populateFrom(FoodItem i) {
        name.setText(i.name);
        count.setText(i.count);
        brand.setText(i.brand);
    }
}

逻辑猫

java.lang.NullPointerException
            at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:330)
            at android.widget.ListView.setAdapter(ListView.java:486)
            at com.smart_mat.dev.fragments.SearchFragment.onCreateView(
SearchFragment.java:86)
            at android.support.v4.app.Fragment.performCreateView(Fragment.java:1786)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1126)
            at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
            at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
            at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:454)
            at android.os.Handler.handleCallback(Handler.java:733)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5433)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1268)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1084)
            at dalvik.system.NativeStart.main(Native Method)

Answer 1

你的 item 变量在 adapter = new SearchAdapter(getActivity(), R.layout.row, item); 中是 null，所以先实例化它。