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来完成我想要的事情，这对这里的大多数人来说可能很容易，但我陷入了这个困境使用这个Navigation Drawer View Pager尝试用此 Custom ListView with Volley 填充选项卡一 fragment .
我想将自定义 ListView 的 MainActivity.java 中的代码传输到抽屉导航中的选项卡 fragment ，但出现错误。
fragment 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 Activity
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);
}
两个代码
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
处收到错误adapter = new CustomListAdapter(this, movieList);
和
pDialog = new ProgressDialog(this);
constructor is undefined
但是它们在示例中都编译得很好。
这是运行代码后得到的 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
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;
}
最佳答案
在您的 Manifest 文件中进行此更改:
<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 TabOneFragment 文件中的函数 onCreateView 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。
关于java - 在 fragment 中填充 JSON ListView ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29308378/