故事是这样的，ViewPager中有五个片段，每个片段在ViewPager上出现时都必须运行一个AsyncTask。 我正尝试与正确答案 相同 。 我将我的AsyncTask放在onResumeFragment中，它运行良好。 但是当我成功运行AsyncTask后更新视图时，问题就开始了。因为我在onCreateView内创建的视图(RecyclerView)被null了。我还尝试在onActivityCreated中使用setRetainInstance（true），但它不起作用。
以下是我的代码，
MainActivity.java
这是我的第二个Fragment代码，其余的Fragments目前都是空白的。
以下是我的代码，
MainActivity.java
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//Tab & Pager
viewPager = (ViewPager) findViewById(R.id.main_tab_content);
adapter = new ViewPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
addPagerListener();
}
private void addPagerListener(){
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageSelected(int newPosition) {
FragmentLifecycle fragmentToShow = (FragmentLifecycle)adapter.getItem(newPosition);
fragmentToShow.onResumeFragment();
FragmentLifecycle fragmentToHide = (FragmentLifecycle)adapter.getItem(currentPosition);
fragmentToHide.onPauseFragment();
currentPosition = newPosition;
}
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
class ViewPagerAdapter extends FragmentPagerAdapter {
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
@Override
public Fragment getItem(int position) {
switch (position){
case 0: return new HomeFragment();
case 1: return new ArtistFragment();
case 2: return new AlbumsFragment();
case 3: return new CollectionsFragment();
case 4: return new SavedFragments();
default: return null;
}
}
@Override
public int getCount() {
return 5;
}
}
这是我的第二个Fragment代码，其余的Fragments目前都是空白的。
public class ArtistFragment extends Fragment implements FragmentLifecycle{
@BindView(R.id.recyclerview_frag_artist)
RecyclerView mRecyclerView;
RecyclerView.Adapter mAdapter;
RecyclerView.LayoutManager mLayoutManager;
@BindView(R.id.radioBtnAll_frag_artist)
RadioButton radioAll;
@BindView(R.id.radioBtnMale_frag_artist)
RadioButton radioMale;
@BindView(R.id.radioBtnFemale_frag_artist)
RadioButton radioFemale;
ArrayList<String> vocalistNameList;
Context context;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_artists, container, false);
ButterKnife.bind(this, rootView);
mRecyclerView.setHasFixedSize(true);
mLayoutManager = new LinearLayoutManager(rootView.getContext());
mRecyclerView.setLayoutManager(mLayoutManager);
vocalistNameList = getDummyDS();
mAdapter = new MyListAdapter(vocalistNameList);
mRecyclerView.setAdapter(mAdapter);
radioAll.setChecked(true);
return rootView;
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setRetainInstance(true);
}
private ArrayList<String> getDummyDS(){
ArrayList<String> dataset = new ArrayList<>();
dataset.add("test");
dataset.add("test");
dataset.add("test");
dataset.add("test");
dataset.add("test");
dataset.add("test");
dataset.add("test");
return dataset;
}
private void getVocalistList(Gender gender){
RequestParams params = new RequestParams();
params.put("action","query");
params.put("list","allcategories");
params.put("acprefix","Vocalist-");
params.put("format","json");
params.put("aclimit","5000");
MyRestClient.get("", params, new JsonHttpResponseHandler(){
ProgressDialog progress;
@Override
public void onStart() {
progress = ProgressDialog.show(AppConstants.activity, "Please wait",
"Loading data..", true);
progress.setCancelable(true);
}
@Override
public void onSuccess(int statusCode, Header[] headers, JSONObject response) {
progress.dismiss();
vocalistNameList = new ArrayList<String>();
try {
JSONArray vocalListJsonArray = response.getJSONObject("query").getJSONArray("allcategories");
for(int i=0; i<vocalListJsonArray.length(); i++){
String vocalListName = vocalListJsonArray.getJSONObject(i).getString("*").replace("Vocalist-","");
vocalistNameList.add(vocalListName);
}
mAdapter = new MyListAdapter(vocalistNameList);
mRecyclerView.setAdapter(mAdapter); // <= RecyclerView is null and app is crashing
mAdapter.notifyDataSetChanged();
} catch (JSONException e) {
e.printStackTrace();
}
}
@Override
public void onFailure(int statusCode, Header[] headers, String responseString, Throwable throwable) {
progress.dismiss();
Log.i("failure", "failed "+statusCode);
}
});
}
@Override
public void onPauseFragment() {
Toast.makeText(AppConstants.applicationContext, "onPauseFragment():", Toast.LENGTH_SHORT).show();
}
@Override
public void onResumeFragment() {
getVocalistList(Gender.All);
Toast.makeText(AppConstants.applicationContext, "onResumeFragment(): Artist", Toast.LENGTH_SHORT).show();
}
我已经一个星期以来一直在尝试解决这个问题。有什么想法吗？
（P.S 我正在使用Android异步Http客户端代替AsyncTask）