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在片段中填充JSON列表视图

android-listview android-fragments listview android java

Derrick · 技术社区 · 10 年前

我是java/android编程的初学者,但我试图添加不同的教程来创建一个定制的应用程序,它可以满足我的需求,这对这里的大多数人来说可能很容易,但我一直在使用这个 Navigation Drawer View Pager 试图用这个 Custom ListView with Volley .

我想在 主要活动.java 将自定义列表视图转换为导航抽屉中的选项卡片段,但我收到错误。

片段选项卡

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;
}

我在以下位置出错

adapter = new CustomListAdapter(this, movieList);

和

pDialog = new ProgressDialog(this);

构造函数未定义

然而,它们在示例中都能很好地编译。

这是我运行代码后得到的日志:

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
自定义适配器列表

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;
}

4 回复 | 直到 10 年前

albert 9 年前

在您的 Manifest 文件:

<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">

在您的 TabOneFragment 函数中的文件 onCreateView ,更改此行

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

到

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

这将解决您的问题。

Anderson K 10 年前

在你的课堂上 TabOneFragment 更改为:

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

和

pDialog = new ProgressDialog(getActivity());

自定义适配器列表

 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;
        }
    }

Arlind Hajredinaj 10 年前

在TabOneFragment类中更改

adapter = new CustomListAdapter(this, movieList);

到

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

和

 pDialog = new ProgressDialog(this);

到

pDialog = new ProgressDialog(getActivity());

这两个构造函数都接受Context而不是Fragment,因此基本上在Fragment类中不能调用它,但必须使用getActivity()

Community CDub 8 年前

我发现了,觉得这对其他人有帮助 check this question 我失踪了

android:name=".AppController" 在我的清单上

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