Question

我遇到了json解析器的listview问题！

（ArretsFragment.java）：

package activity;

import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;

import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonArrayRequest;
import com.example.pierre.tan.R;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.List;

import adapter.CustomListAdapter;
import app.AppController;
import model.Movie;


public class ArretsFragment extends Fragment {

// Log tag
private static final String TAG = MainActivity.class.getSimpleName();

// Movies json url
private static final String url = "http://api.androidhive.info/json/movies.json";
private List<Movie> movieList = new ArrayList<Movie>();
private ListView listView;
private CustomListAdapter adapter;


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

@Override
public void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);


    listView = (ListView) getActivity().findViewById(R.id.list);
    adapter = new CustomListAdapter(getActivity(), movieList);
    listView.setAdapter(adapter);

    // Showing progress dialog before making http request



    // Creating volley request obj
    JsonArrayRequest movieReq = new JsonArrayRequest(url,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    Log.d(TAG, response.toString());


                    // Parsing json
                    for (int i = 0; i < response.length(); i++) {
                        try {

                            JSONObject obj = null;
                            try {
                                obj = response.getJSONObject(i);
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                            Movie movie = new Movie();
                            movie.setTitle(obj.getString("title"));
                            movie.setThumbnailUrl(obj.getString("image"));
                            movie.setRating(((Number) obj.get("rating"))
                                    .doubleValue());
                            movie.setYear(obj.getInt("releaseYear"));

                            // Genre is json array
                            JSONArray genreArry = obj.getJSONArray("genre");
                            ArrayList<String> genre = new ArrayList<String>();
                            for (int j = 0; j < genreArry.length(); j++) {
                                genre.add((String) genreArry.get(j));
                            }
                            movie.setGenre(genre);

                            // adding movie to movies array
                            movieList.add(movie);

                        } catch (JSONException e) {
                            e.printStackTrace();
                        }

                    }

                    // notifying list adapter about data changes
                    // so that it renders the list view with updated data
                    adapter.notifyDataSetChanged();
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            VolleyLog.d(TAG, "Error: " + error.getMessage());


        }


    });

    // Adding request to request queue
    AppController.getInstance().addToRequestQueue(movieReq);

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_arrets, container, false);


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

@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
}

@Override
public void onDetach() {
    super.onDetach();
}
}

我已经得到了这个（CustomListAdapter.java）：

package adapter;


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 com.example.pierre.tan.R;

import java.util.List;

import app.AppController;
import model.Movie;



public class CustomListAdapter extends BaseAdapter {
private Activity activity;
private LayoutInflater inflater;
private List<Movie> movieItems;
ImageLoader imageLoader = AppController.getInstance().getImageLoader();

public CustomListAdapter(Activity activity, List<Movie> movieItems) {
    this.activity = activity;
    this.movieItems = movieItems;
}

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

@Override
public Object getItem(int location) {
    return movieItems.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_row, null);

    if (imageLoader == null)
        imageLoader = AppController.getInstance().getImageLoader();
    NetworkImageView thumbNail = (NetworkImageView) convertView
            .findViewById(R.id.thumbnail);
    TextView title = (TextView) convertView.findViewById(R.id.title);
    TextView rating = (TextView) convertView.findViewById(R.id.rating);
    TextView genre = (TextView) convertView.findViewById(R.id.genre);
    TextView year = (TextView) convertView.findViewById(R.id.releaseYear);

    // getting movie data for the row
    Movie m = movieItems.get(position);

    // thumbnail image
    thumbNail.setImageUrl(m.getThumbnailUrl(), imageLoader);

    // title
    title.setText(m.getTitle());

    // rating
    rating.setText("Rating: " + String.valueOf(m.getRating()));

    // genre
    String genreStr = "";
    for (String str : m.getGenre()) {
        genreStr += str + ", ";
    }
    genreStr = genreStr.length() > 0 ? genreStr.substring(0,
            genreStr.length() - 2) : genreStr;
    genre.setText(genreStr);

    // release year
    year.setText(String.valueOf(m.getYear()));

    return convertView;
}

}

当我尝试申请时，我发现了这些错误：

04-16 11:14:57.416  27043-27043/com.example.pierre.tan E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.pierre.tan, PID: 27043
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
        at activity.ArretsFragment.onCreate(ArretsFragment.java:55)
        at android.support.v4.app.Fragment.performCreate(Fragment.java:1763)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:915)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1136)
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:739)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1499)
        at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:456)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5254)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

这是一个有点困难的过程，所以如果有人可以帮助我，那将是非常好的

Answer 1

你的问题在里面：

listView = (ListView) getActivity().findViewById(R.id.list);

您的活动不包含您的listView。

将所有这些添加到onActivityCreated()方法

listView = (ListView) getView().findViewById(R.id.list);
adapter = new CustomListAdapter(getActivity(), movieList);
listView.setAdapter(adapter);

并学习片段lifecycle。

Answer 2

您将一组空的电影解析到您的适配器：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    listView = (ListView) getActivity().findViewById(R.id.list);
    // movieList is an empty array at this point.
    adapter = new CustomListAdapter(getActivity(), movieList);
    listView.setAdapter(adapter);

    // ...
}

我猜你只需要在使用movieReq请求中的数据填充列表后再设置适配器。

Answer 3

在检索列表视图之前，您必须对布局进行充气。

在片段中，使用onCreateView方法执行所有处理。

@Override
public void onCreate(Bundle savedInstanceState) {


    super.onCreate(savedInstanceState);

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_arrets, container, false);

  listView = (ListView) getActivity().findViewById(R.id.list);
    adapter = new CustomListAdapter(getActivity(), movieList);
    listView.setAdapter(adapter);

    // Showing progress dialog before making http request



    // Creating volley request obj
    JsonArrayRequest movieReq = new JsonArrayRequest(url,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    Log.d(TAG, response.toString());


                    // Parsing json
                    for (int i = 0; i < response.length(); i++) {
                        try {

                            JSONObject obj = null;
                            try {
                                obj = response.getJSONObject(i);
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                            Movie movie = new Movie();
                            movie.setTitle(obj.getString("title"));
                            movie.setThumbnailUrl(obj.getString("image"));
                            movie.setRating(((Number) obj.get("rating"))
                                    .doubleValue());
                            movie.setYear(obj.getInt("releaseYear"));

                            // Genre is json array
                            JSONArray genreArry = obj.getJSONArray("genre");
                            ArrayList<String> genre = new ArrayList<String>();
                            for (int j = 0; j < genreArry.length(); j++) {
                                genre.add((String) genreArry.get(j));
                            }
                            movie.setGenre(genre);

                            // adding movie to movies array
                            movieList.add(movie);

                        } catch (JSONException e) {
                            e.printStackTrace();
                        }

                    }

                    // notifying list adapter about data changes
                    // so that it renders the list view with updated data
                    adapter.notifyDataSetChanged();
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            VolleyLog.d(TAG, "Error: " + error.getMessage());


        }


    });

    // Adding request to request queue
    AppController.getInstance().addToRequestQueue(movieReq);

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

ListView和SetAdapter空指针异常

3 个答案: