片段内部的自定义列表不起作用

  • Z时代
  • 2024-01-10
  • 分类：问答

我已经简单地在fragment中使用了一个自定义列表。我使用volley从api中检索了这些数据。它显示了以下错误。我有任何想法解决这个问题，有人可以帮助我。片段内部的自定义列表不起作用

java.lang.NullPointerException: Attempt to invoke virtual method 'com.android.volley.toolbox.ImageLoader com.example.user.ekta.AppController.getImageLoader()' on a null object reference 
                      at com.example.user.ekta.MyBookAdapter.<init>(MyBookAdapter.java:25) 
                      at com.example.user.ekta.FullInfoTabFragment.onCreateView(FullInfoTabFragment.java:85).

这是我的片段类

package com.example.user.ekta; 
import android.app.ProgressDialog; 
import android.content.Context; 
import android.content.Intent; 
import android.content.res.TypedArray; 
import android.graphics.Canvas; 
import android.graphics.drawable.Drawable; 
import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v4.app.Fragment; 
import android.support.v4.content.ContextCompat; 
import android.support.v7.widget.DefaultItemAnimator; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.support.v7.widget.Toolbar; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.Toast; 
import com.android.volley.Response; 
import com.android.volley.VolleyError; 
import com.android.volley.VolleyLog; 
import com.android.volley.toolbox.JsonArrayRequest; 
import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 
import java.util.ArrayList; 
import java.util.List; 
public class FullInfoTabFragment extends Fragment { 
    private static final String EXTRA_SRORT_CARD_MODEL = "EXTRA_SRORT_CARD_MODEL"; 
    // String transitionTag; 
    private SportCardModel sportCardModel; 
    private Toolbar toolbar; 
    private ImageView ivPhoto; 
    private static final String TAG = FullInfoTabFragment.class.getSimpleName(); 
    private static final String url = "http://myeducationhunt.com/public/schools"; 
    private ProgressDialog pDialog; 
    private List<MyBook> ourBooksListItems = new ArrayList<MyBook>(); 
    private ListView listView; 
    private MyBookAdapter adapter; 
    public static FullInfoTabFragment newInstance(SportCardModel sportCardModel) { 
     FullInfoTabFragment fragment = new FullInfoTabFragment(); 
     Bundle args = new Bundle(); 
     args.putParcelable(EXTRA_SRORT_CARD_MODEL, sportCardModel); 
     fragment.setArguments(args); 
     return fragment; 
    } 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     if (getArguments() != null) { 
      sportCardModel = getArguments().getParcelable(EXTRA_SRORT_CARD_MODEL); 
     } 
     if (savedInstanceState != null) { 
      sportCardModel = savedInstanceState.getParcelable(EXTRA_SRORT_CARD_MODEL); 
     } 
    } 
    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     View view = inflater.inflate(R.layout.fragment_full_info, container, false); 
     toolbar = (Toolbar) view.findViewById(R.id.toolbar); 
     ivPhoto = (ImageView) view.findViewById(R.id.ivPhoto); 
     listView = (ListView) view.findViewById(R.id.list); 
     adapter = new MyBookAdapter(getActivity(), ourBooksListItems); 
     listView.setAdapter(adapter); 
     listView.setTextFilterEnabled(true); 
     listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
      @Override 
      public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
//    OurSchool ourSchool = new OurSchool(); 
//    Intent i = new Intent(getContext(), SchoolDetails.class); 
//    i.putExtra("id", ourSchoolsListItems.get(position).schoolId); 
//    i.putExtra("name", ourSchoolsListItems.get(position).schoolName); 
//    i.putExtra("location", ourSchoolsListItems.get(position).schoolLocation); 
//    i.putExtra("logo", ourSchoolsListItems.get(position).schoolLogo); 
//    i.putExtra("email", ourSchoolsListItems.get(position).schoolEmail); 
//    i.putExtra("website", ourSchoolsListItems.get(position).schoolWebsite); 
//    i.putExtra("created_at", ourSchoolsListItems.get(position).createdAt); 
//    i.putExtra("updated_at", ourSchoolsListItems.get(position).updatedAt); 
//    startActivity(i); 
      } 
     }); 
     pDialog = new ProgressDialog(getActivity()); 
// Showing progress dialog before making http request 
     pDialog.setMessage("Loading…"); 
     pDialog.show(); 
// Creating volley request obj 
     JsonArrayRequest schoolRequest = new JsonArrayRequest(url, 
       new Response.Listener<JSONArray>() { 
        @Override 
        public void onResponse(JSONArray response) { 
         Log.d(TAG, response.toString()); 
         pDialog.hide(); 
         // Parsing json 
         for (int i = 0; i < response.length(); i++) { 
          try { 
           JSONObject obj = response.getJSONObject(i); 
           MyBook myBook = new MyBook(); 
           myBook.bookName = obj.getString("name"); 
           myBook.bookAuthor = obj.getString("location"); 
           myBook.bookCover= obj.getString("logo"); 
           // adding schools to ourSchool list 
           ourBooksListItems.add(myBook); 
          } catch (JSONException e) { 
           e.printStackTrace(); 
          } 
         } 
         adapter.notifyDataSetChanged(); 
        } 
       }, new Response.ErrorListener() { 
      @Override 
      public void onErrorResponse(VolleyError error) { 
       VolleyLog.d(TAG, "Error: " + error.getMessage()); 
       pDialog.hide(); 
      } 
     }); 
     // Adding request to request queue 
     AppController.getInstance().addToRequestQueue(schoolRequest); 
     return view; 
    } 
    @Override 
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { 
     super.onViewCreated(view, savedInstanceState); 
     toolbar.setTitle(sportCardModel.getSportTitle()); 
     toolbar.setNavigationIcon(R.drawable.ic_back); 
     toolbar.setNavigationOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       getActivity().onBackPressed(); 
      } 
     }); 
     toolbar.setBackgroundColor(ContextCompat.getColor(getContext(), sportCardModel.getBackgroundColorResId())); 
     ivPhoto.setImageResource(sportCardModel.getImageResId()); 
    } 
    @Override 
    public void onSaveInstanceState(Bundle outState) { 
     outState.putParcelable(EXTRA_SRORT_CARD_MODEL, sportCardModel); 
     super.onSaveInstanceState(outState); 
    } 
    static class DividerItemDecoration extends RecyclerView.ItemDecoration { 
     private static final int[] ATTRS = new int[]{android.R.attr.listDivider}; 
     private Drawable mDivider; 
     /** 
     * Default divider will be used 
     */ 
     public DividerItemDecoration(Context context) { 
      final TypedArray styledAttributes = context.obtainStyledAttributes(ATTRS); 
      mDivider = styledAttributes.getDrawable(0); 
      styledAttributes.recycle(); 
     } 
     /** 
     * Custom divider will be used 
     */ 
     public DividerItemDecoration(Context context, int resId) { 
      mDivider = ContextCompat.getDrawable(context, resId); 
     } 
     @Override 
     public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) { 
      int left = parent.getPaddingLeft(); 
      int right = parent.getWidth() - parent.getPaddingRight(); 
      int childCount = parent.getChildCount(); 
      for (int i = 0; i < childCount; i++) { 
       View child = parent.getChildAt(i); 
       RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams(); 
       int top = child.getBottom() + params.bottomMargin; 
       int bottom = top + mDivider.getIntrinsicHeight(); 
       mDivider.setBounds(left, top, right, bottom); 
       mDivider.draw(c); 
      } 
     } 
    } 
}

这是我的适配器类

package com.example.user.ekta; 
import android.app.Activity; 
import android.content.Context; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.BaseAdapter; 
import android.widget.TextView; 
import com.android.volley.toolbox.ImageLoader; 
import com.android.volley.toolbox.NetworkImageView; 
import java.util.List; 
/** 
* Created by user on 11/27/2016. 
*/ 
public class MyBookAdapter extends BaseAdapter { 
    private Activity activity; 
    private LayoutInflater inflater; 
    private List<MyBook> ourbooksList; 
    ImageLoader imageLoader = AppController.getInstance().getImageLoader(); 
    public MyBookAdapter(Activity activity, List<MyBook> ourbooksListsList) { 
     this.activity = activity; 
     this.ourbooksList = ourbooksListsList; 
    } 
    @Override 
    public int getCount() { 
     return ourbooksList.size(); 
    } 
    @Override 
    public Object getItem(int location) { 
     return ourbooksList.get(location); 
    } 
    @Override 
    public long getItemId(int position) { 
     return position; 
    } 
    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
     if (inflater == null) 
      inflater = (LayoutInflater) activity 
        .getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
     if (convertView == null) 
      convertView = inflater.inflate(R.layout.list_books, null); 
     if (imageLoader == null) 
      imageLoader = AppController.getInstance().getImageLoader(); 
     NetworkImageView bookCover = (NetworkImageView) convertView 
       .findViewById(R.id.bookCover); 
     TextView bookName = (TextView) convertView.findViewById(R.id.bookName); 
     TextView boookAuthor = (TextView) convertView.findViewById(R.id.bookAuthor); 
     MyBook m = ourbooksList.get(position); 
     bookCover.setImageUrl(m.getBookCover(), imageLoader); 
     bookName.setText("Name: " + m.getBookName()); 
     boookAuthor.setText("Address: " + String.valueOf(m.getBookAuthor())); 
     return convertView; 
    } 
}

回答：

AppController.getInstance（）的返回null，您尚未初始化的AppController。

如果AppController的扩展您的应用程序，那么你必须改变你的清单

安卓：在应用部分的名称=“路径AppController的”。

以上是 片段内部的自定义列表不起作用 的全部内容， 来源链接： utcz.com/qa/257338.html

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