在片段中填充JSON listview

Question

我是Java / android编程的初学者，但是我试图添加不同的教程来创建可以满足我需要的自定义应用程序，这对大多数人来说可能很容易，但是我被困在尝试使用此功能的过程中导航抽屉视图分页器试图使用Volley将此Custom ListView填充到选项卡一个片段。

我想将自定义listview的MainActivity.java中的代码传输到导航抽屉中的选项卡片段，但出现错误。

片段标签

public class TabTwoFragment extends Fragment{

private TextView txtFragmenttwo;

public static TabTwoFragment newInstance() {
    Bundle bundle = new Bundle();

    TabTwoFragment fragment = new TabTwoFragment();
    fragment.setArguments(bundle);

    return fragment;
}   

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

    View rootView = inflater.inflate(R.layout.two_fragment, container, false);

    txtFragmenttwo = (TextView) rootView.findViewById(R.id.txtFragmentTwo);
    txtFragmenttwo.setText(R.string.fragment_tab_two);

    rootView.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT ));       
    return rootView;
}

@Override
public void onActivityCreated(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onActivityCreated(savedInstanceState);
    setHasOptionsMenu(true);
}`

主要活动

public class MainActivity extends Activity {
// 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 ProgressDialog pDialog;
private List<Movie> movieList = new ArrayList<Movie>();
private ListView listView;
private CustomListAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

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

    pDialog = new ProgressDialog(this);
    // Showing progress dialog before making http request
    pDialog.setMessage("Loading...");
    pDialog.show();

    // changing action bar color
    getActionBar().setBackgroundDrawable(
            new ColorDrawable(Color.parseColor("#1b1b1b")));

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

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

                            JSONObject obj = response.getJSONObject(i);
                            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());
                    hidePDialog();

                }
            });

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

两种代码

public class TabOneFragment extends Fragment{

private static final String TAG = TabOneFragment.class.getSimpleName();

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

@Override
public void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
}

public static TabOneFragment newInstance() {
    TabOneFragment fragment = new TabOneFragment();
    return fragment;
}   

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

    View rootView = inflater.inflate(R.layout.one_fragment, container, false);
    //txtFragmentone = (TextView) rootView.findViewById(R.id.txtFragmentOne);
    //txtFragmentone.setText(R.string.fragment_tab_one);
    rootView.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT ));

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

    adapter = new CustomListAdapter(this, movieList);
    listView.setAdapter(adapter);

    pDialog = new ProgressDialog(this);
    // Showing progress dialog before making http request
    pDialog.setMessage("Loading...");
    pDialog.show();

    // changing action bar color
    getActivity().getActionBar().setBackgroundDrawable(
            new ColorDrawable(Color.parseColor("#1b1b1b")));

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

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

                            JSONObject obj = response.getJSONObject(i);
                            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());
                    hidePDialog();

                }
            });

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

    return rootView;
}

我在错误

adapter = new CustomListAdapter(this, movieList);

和

pDialog = new ProgressDialog(this);

构造函数未定义

然而，它们在示例中的汇编都很好。

这是运行代码后的logcat：

03-27 22:30:57.085: E/AndroidRuntime(10963): FATAL EXCEPTION: main
03-27 22:30:57.085: E/AndroidRuntime(10963): java.lang.NullPointerException
03-27 22:30:57.085: E/AndroidRuntime(10963):    at info.androidhive.customlistviewvolley.adater.CustomListAdapter.<init>(CustomListAdapter.java:24)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at br.liveo.fragments.TabOneFragment.onCreateView(TabOneFragment.java:75)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:938)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1115)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1478)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:478)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.view.View.measure(View.java:12773)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.widget.LinearLayout.measureVertical(LinearLayout.java:815)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.widget.LinearLayout.onMeasure(LinearLayout.java:553)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.view.View.measure(View.java:12773)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4788)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.view.View.measure(View.java:12773)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4788)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.widget.FrameLayout.onMeasure(FrameLayout.java:293)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.view.View.measure(View.java:12773)
03-27 22:30:57.085: E/AndroidRuntime(10963):    at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:704)

编辑2
CustomAdapterList

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;
}

Answer 1

在Manifest文件中进行以下更改：

<application
android:name=".AppController" //this one (your path to AppController file)
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">

在函数onCreateView TabOneFragment文件中，更改此行

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

至

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

这将解决您的问题。

Answer 2

在您的类TabOneFragment更改为：

adapter = new CustomListAdapter(getActivity(), movieList);

和

pDialog = new ProgressDialog(getActivity());

CustomAdapterList

 public class CustomListAdapter extends BaseAdapter {

        private Activity activity;
        private LayoutInflater inflater;
        private List<Movie> movieItems = new ArrayList<>();
        ImageLoader imageLoader = AppController.getInstance().getImageLoader();

        public CustomListAdapter(Activity activity, List<Movie> movieItems) {
            this.activity = activity;
            this.movieItems = movieItems;
            inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }

        @Override
        public int getCount() {
            return movieItems != null ? movieItems.size() : 0;
        }

        @Override
        public Object getItem(int location) {
            return movieItems != null ? movieItems.get(location) : null;
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

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

            if (convertView == null)
                convertView = inflater.inflate(R.layout.list_row, parent, false);

            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;
        }
    }

Answer 3

在TabOneFragment类中更改

adapter = new CustomListAdapter(this, movieList);

至

adapter = new CustomListAdapter(getActivity(), movieList);

和

 pDialog = new ProgressDialog(this);

至

pDialog = new ProgressDialog(getActivity());

两个构造函数都接受一个Context而不是一个Fragment，因此基本上在您的fragment类中您不能调用此方法，但必须使用getActivity（）

Answer 4

我发现了，认为这可帮助其他人检查这个问题，我失踪

清单中的android:name=".AppController"

<application
    android:name=".AppController" //this one
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme">