我有像
这样的片段public class FeedFragment extends Fragment {
private static final String TAG = FeedFragment.class.getSimpleName();
private ListView listView;
private FeedListAdapter listAdapter;
private List<FeedItem> feedItems;
private String URL_FEED = "http://api.androidhive.info/feed/feed.json";
private FragmentActivity fragmentActivity;
private Activity mActivity;
public static FeedFragment newInstance (){
FeedFragment feedFragment = new FeedFragment();
return feedFragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.feed_fragment, container, false);
fragmentActivity = (FragmentActivity) super.getActivity();
listView = (ListView) view.findViewById(R.id.list);
feedItems = new ArrayList<>();
listAdapter = new FeedListAdapter(mActivity, feedItems);
listView.setAdapter(listAdapter);
Cache cache = AppController.getInstance().getRequestQueue().getCache();
Cache.Entry entry = cache.get(URL_FEED);
if (entry != null){
try {
String data = new String (entry.data, "UTF-8");
try {
parseJsonFeed(new JSONObject(data));
} catch (JSONException e){
e.printStackTrace();
}
}catch (UnsupportedEncodingException e){
e.printStackTrace();
}
} else {
JsonObjectRequest jsonReq = new JsonObjectRequest(Request.Method.GET,
URL_FEED, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
VolleyLog.d(TAG, "Response:" + response.toString());
if (response != null){
parseJsonFeed(response);
}
}
},new Response.ErrorListener(){
@Override
public void onErrorResponse(VolleyError error) {
VolleyLog.d(TAG, "ERROR:" + error.getMessage());
}
});
AppController.getInstance().addToRequestQueue(jsonReq);
}
return view;
}
private void parseJsonFeed(JSONObject response){
try {
JSONArray feedArray = response.getJSONArray("feed");
for (int i = 0;i < feedArray.length(); i++){
JSONObject feedObj = (JSONObject) feedArray.get(i);
FeedItem item = new FeedItem();
item.setId(feedObj.getInt("id"));
item.setName(feedObj.getString("name"));
String image = feedObj.isNull("image")? null : feedObj
.getString("image");
item.setImge(image);
item.setStatus(feedObj.getString("status"));
item.setProfilePic(feedObj.getString("profilePic"));
item.setTimeStamp(feedObj.getString("timeStamp"));
String feedUrl = feedObj.isNull("url")? null : feedObj
.getString("url");
item.setUrl(feedUrl);
feedItems.add(item);
}
listAdapter.notifyDataSetChanged();
} catch (JSONException e){
e.printStackTrace();
}
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mActivity = activity;
}
这是适配器
public class FeedListAdapter extends BaseAdapter{
private Activity activity;
private LayoutInflater inflater;
private List<FeedItem> feedItems;
ImageLoader imageLoader = AppController.getInstance().getImageLoader();
public FeedListAdapter(Activity activity, List<FeedItem> feedItems) {
this.activity = activity;
this.feedItems = feedItems;
}
@Override
public int getCount() {
return feedItems.size();
}
@Override
public Object getItem(int location) {
return feedItems.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.feed_litem_list, null);
if (imageLoader == null)
imageLoader = AppController.getInstance().getImageLoader();
TextView name = (TextView) convertView.findViewById(R.id.client_name);
TextView timestamp = (TextView) convertView
.findViewById(R.id.time_stamp);
TextView statusMsg = (TextView) convertView
.findViewById(R.id.txtStatusMgs);
TextView url = (TextView) convertView.findViewById(R.id.txtUrl);
NetworkImageView profilePic = (NetworkImageView) convertView
.findViewById(R.id.profile_pic);
FeedImageView feedImageView = (FeedImageView) convertView
.findViewById(R.id.feedImage1);
FeedItem item = feedItems.get(position);
name.setText(item.getName());
// Converting timestamp into x ago format
CharSequence timeAgo = DateUtils.getRelativeTimeSpanString(
Long.parseLong(item.getTimeStamp()),
System.currentTimeMillis(), DateUtils.SECOND_IN_MILLIS);
timestamp.setText(timeAgo);
// Chcek for empty status message
if (!TextUtils.isEmpty(item.getStatus())) {
statusMsg.setText(item.getStatus());
statusMsg.setVisibility(View.VISIBLE);
} else {
// status is empty, remove from view
statusMsg.setVisibility(View.GONE);
}
// Checking for null feed url
if (item.getUrl() != null) {
url.setText(Html.fromHtml("<a href=\"" + item.getUrl() + "\">"
+ item.getUrl() + "</a> "));
// Making url clickable
url.setMovementMethod(LinkMovementMethod.getInstance());
url.setVisibility(View.VISIBLE);
} else {
// url is null, remove from the view
url.setVisibility(View.GONE);
}
// user profile pic
profilePic.setImageUrl(item.getProfilePic(), imageLoader);
// Feed image
if (item.getImge() != null) {
feedImageView.setImageUrl(item.getImge(), imageLoader);
feedImageView.setVisibility(View.VISIBLE);
feedImageView
.setResponseObserver(new FeedImageView.ResponseObserver() {
@Override
public void onError() {
}
@Override
public void onSuccess() {
}
});
} else {
feedImageView.setVisibility(View.GONE);
}
return convertView;
}
现在错误显示为
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
at com.evolustudios.askin.askin.src.fragments.FeedFragment.onCreateView(FeedFragment.java:63)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:2080)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1108)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1290)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:801)
at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1638)
at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:679)
at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1240)
at android.support.v4.view.ViewPager.populate(ViewPager.java:1088)
at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1614)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.design.widget.CoordinatorLayout.onMeasureChild(CoordinatorLayout.java:706)
at android.support.design.widget.HeaderScrollingViewBehavior.onMeasureChild(HeaderScrollingViewBehavior.java:90)
at android.support.design.widget.AppBarLayout$ScrollingViewBehavior.onMeasureChild(AppBarLayout.java:1364)
at android.support.design.widget.CoordinatorLayout.onMeasure(CoordinatorLayout.java:771)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:389)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1508)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
这是FeedItem
public class FeedItem {
private int id;
private String name, status, image, profilePic, timeStamp, url;
public FeedItem() {
}
public FeedItem(int id, String name, String image, String status,
String profilePic, String timeStamp, String url) {
super();
this.id = id;
this.name = name;
this.image = image;
this.status = status;
this.profilePic = profilePic;
this.timeStamp = timeStamp;
this.url = url;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getImge() {
return image;
}
public void setImge(String image) {
this.image = image;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
public String getProfilePic() {
return profilePic;
}
public void setProfilePic(String profilePic) {
this.profilePic = profilePic;
}
public String getTimeStamp() {
return timeStamp;
}
public void setTimeStamp(String timeStamp) {
this.timeStamp = timeStamp;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
我不知道为什么会返回null。如果我将它转换为活动，Feed Fragment工作正常。但在一个片段中它不起作用。 任何人都可以向我解释一下，
是的，我知道它是一个空指针异常。但是在哪里创建零点？