使用 recyclerview 和 Asynctask 设置 Viewpager
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【中文标题】使用 recyclerview 和 Asynctask 设置 Viewpager【英文标题】：Setup Viewpager with recyclerview and Asynctask 【发布时间】：2018-12-18 21:06:39 【问题描述】：我有一个 ViewPager 和 3 个 Fragment，根据 android 文档，ViewPager.setOffscreenPageLimit(1); 至少是 1 个。当我在ViewPager 中有多个Fragments 并且每个Fragment 必须从Server 加载一些数据时，我遇到了一个问题，因此我在每个Fragment 中调用AsyncTask，然后先获取数据加载到Fragment。
我可以在Log 中看到我正在从Server 获取数据，但是当我调用第二个Fragment 时，我可以看到它也在调用下一个Fragment onCreateView 这就是为什么我我很难设置RecyclerView。我尝试通过adapter3.notifyDataSetChanged(); 在不同情况下调用Adapter，但没有任何帮助。
ViewPager 的父 Fragment。
public class ViewUserProfile extends Fragment
ViewPager ViewPager;
UserProfile_TabAdapter tabAdapter;
TabLayout tabLayout;
View view;
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState)
view = inflater.inflate(R.layout.view_userprofile, container, false);
ViewPager = view.findViewById(R.id.up_Viewpager_ViewPager);
ViewPager.setOffscreenPageLimit(1);
ViewPager.setPageMargin(10);
tabAdapter=new TabAdapter(getFragmentManager(),getActivity(),Uda.getFN());
tabLayout= view.findViewById(R.id.up_Viewpager_Tab);
tabLayout.setupWithViewPager(userInfo_ViewPager);
return view;
Fragment 没有加载它的数据：
public class UseConnectfragment extends Fragment
RecyclerView FriendsRecycler,FollowingRecylcer,FollowerRecycler;
ArrayList<viewUserProfile_Wrapper> followersList;
ArrayList<viewUserProfile_Wrapper> friendsList;
ArrayList<viewUserProfile_Wrapper> followingList;
UserConnections_Adapter adapter1;
UserConnections_Adapter adapter2;
UserConnections_Adapter adapter3;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState)
View view=inflater.inflate(R.layout.userprofile_connections,container,false);
setRetainInstance(true);
FriendsRecycler=view.findViewById(R.id.userConnections_recyclerFriends);
FollowingRecylcer=view.findViewById(R.id.userConnections_recyclerFollowing);
FollowerRecycler=view.findViewById(R.id.userConnections_recyclerFollower);
FriendsRecycler.setHasFixedSize(true);
FollowingRecylcer.setHasFixedSize(true);
FollowerRecycler.setHasFixedSize(true);
FriendsRecycler.setLayoutManager(new GridLayoutManager(getActivity(), 3));
FollowingRecylcer.setLayoutManager(new GridLayoutManager(getActivity(), 3));
FollowerRecycler.setLayoutManager(new GridLayoutManager(getActivity(), 3));
adapter1=new UserConnections_Adapter(friendsList);
adapter2=new UserConnections_Adapter(followingList);
adapter3=new UserConnections_Adapter(followersList);
return view;
@Override
public void setUserVisibleHint(boolean isVisibleToUser)
super.setUserVisibleHint(isVisibleToUser);
Log.d(TAG,"Set User Visible Running");
if (isVisibleToUser)
Log.d(TAG,"User Connection Tab Is Visible So Call Server Now");
new GetConncetions().execute();
public class UserConnections_Adapter extends RecyclerView.Adapter<UseConnections_fragment.UserConnections_Adapter.ViewHolder>
ArrayList<viewUserProfile_Wrapper> connectionList;
public UserConnections_Adapter(ArrayList<viewUserProfile_Wrapper> connectionList)
this.connectionList = connectionList;
@Override
public UserConnections_Adapter.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i)
LayoutInflater inflater= (LayoutInflater) viewGroup.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View view= inflater.inflate(R.layout.userprofile_connections_singleitem,viewGroup,false);
return new ViewHolder(view);
@Override
public void onBindViewHolder(UserConnections_Adapter.ViewHolder holder, int i)
final viewUserProfile_Wrapper wrapper=connectionList.get(i);
Log.d(TAG,"Wrapper on bind "+wrapper.getUserName()+" "+connectionList.size());
holder.userName.setText(wrapper.getUserName());
Glide.with(getActivity()).load(wrapper.getUserImage()).into(holder.userImage);
holder.userImage.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View view)
Toast.makeText(getActivity(), "User Name "+wrapper.getUserName()+" User ID "+wrapper.getID(), Toast.LENGTH_SHORT).show();
);
@Override
public int getItemCount()
return connectionList.size();
public class ViewHolder extends RecyclerView.ViewHolder
TextView userName;
ImageView userImage;
public ViewHolder(View itemView)
super(itemView);
userName=itemView.findViewById(R.id.userConnection_Name);
userImage=itemView.findViewById(R.id.userConnection_friends);
public class GetConncetions extends AsyncTask<Void,Void,String>
private static final String All_Connections="http://localhost/test/Android/getallon.php";
BufferedReader reader;
private ProgressDialog progressDialog;
@Override
protected void onPreExecute()
super.onPreExecute();
progressDialog = new ProgressDialog(getActivity());
progressDialog.setCancelable(false);
progressDialog.setTitle("Loading...");
progressDialog.show();
@Override
protected String doInBackground(Void... voids)
Log.d(TAG,"Starting Do in background");
// addedInterest=new ArrayList<>();
try
URL url=new URL(All_Connections);
HttpURLConnection connection= (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setDoInput(true);
connection.setDoOutput(true);
connection.connect();
connection.setConnectTimeout(5000);
OutputStream outputStream=connection.getOutputStream();
BufferedWriter writer=new BufferedWriter(new OutputStreamWriter(outputStream,"UTF-8"));
writer.write(data);
writer.flush();
writer.close();
outputStream.close();
//GET INTEREST JSON FROM SERVER
Log.d(TAG,"Response Code "+connection.getResponseCode());
if (connection.getResponseCode()==200)
InputStream inputStream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
StringBuffer stringBuffer = new StringBuffer();
while ((line = reader.readLine()) != null)
stringBuffer.append(line);
Log.d(TAG, "Appending JSON into String Buffer");
Log.d(TAG,"JSON Received "+stringBuffer);
JSONObject jsonObject=new JSONObject(stringBuffer.toString());
String callResult=jsonObject.getString("status");
Log.d(TAG,"Server Call Result "+callResult);
//Make These String out of the scope so we can access this outside if statement
String ID,Name,Image;
if (callResult.equals("SUCCESS"))
Log.d(TAG,"Server Call Is Success");
followersList=new ArrayList<>();
followingList=new ArrayList<>();
friendsList =new ArrayList<>();
JSONArray followerDataArray=jsonObject.getJSONArray("data1");
for (int i = 0; i <followerDataArray.length() ; i++)
String image=followerDataArray.getJSONObject(i).getString("getmyUserImage");
viewUserProfile_Wrapper followerData=new viewUserProfile_Wrapper(image);
followersList.add(followerData);
JSONArray followingDataArray=jsonObject.getJSONArray("data2");
for (int i = 0; i <followingDataArray.length() ; i++)
String image=followerDataArray.getJSONObject(i).getString("getmyUserImage");
viewUserProfile_Wrapper followerData=new viewUserProfile_Wrapper(image);
followingList.add(followerData);
JSONArray friendDataArray=jsonObject.getJSONArray("data3");
for (int i = 0; i <friendDataArray.length() ; i++)
String image=followerDataArray.getJSONObject(i).getString("getmyUserImage");
viewUserProfile_Wrapper followerData=new viewUserProfile_Wrapper(image);
friendsList.add(followerData);
return null;
return "Success";
catch (MalformedURLException e)
e.printStackTrace();
catch (IOException e)
e.printStackTrace();
catch (JSONException e)
e.printStackTrace();
return null;
@Override
protected void onPostExecute(String v)
super.onPostExecute(v);
Log.d(TAG,"On Post running");
progressDialog.dismiss();
if (v!=null)
if (v.equals("Success"))
FriendsRecycler.setAdapter(adapter1);
FollowingRecylcer.setAdapter(adapter2);
FollowerRecycler.setAdapter(adapter3);
else
Toast.makeText(getActivity(), "Server Error.Try Again", Toast.LENGTH_SHORT).show();
【问题讨论】：
在doInBackground里面，在3个for-loop之后，有return null。我认为它不应该在那里。希望有帮助！
@I_A_Mok 感谢您的评论，但即使删除 null 后它也不起作用。
@I_A_Mok 我只注意到如果我初始化适配器onPostExecute 然后它工作。 adapter=new fetchPhoto_Adapter();
【参考方案1】：
当片段可见时调用您的 asynctask 将其添加到您的片段中
编辑
更改以下代码
JSONArray followingDataArray = jsonObject.getJSONArray("data2");
for (int i = 0; i < followingDataArray.length(); i++)
String image = followerDataArray.getJSONObject(i).getString("getmyUserImage");
viewUserProfile_Wrapper followerData = new viewUserProfile_Wrapper(image);
followingList.add(followerData);
JSONArray friendDataArray = jsonObject.getJSONArray("data3");
for (int i = 0; i < friendDataArray.length(); i++)
String image = followerDataArray.getJSONObject(i).getString("getmyUserImage");
viewUserProfile_Wrapper followerData = new viewUserProfile_Wrapper(image);
friendsList.add(followerData);
到这里
JSONArray followingDataArray = jsonObject.getJSONArray("data2");
for (int i = 0; i < followingDataArray.length(); i++)
String image = followingDataArray.getJSONObject(i).getString("getmyUserImage");
viewUserProfile_Wrapper followerData = new viewUserProfile_Wrapper(image);
followingList.add(followerData);
JSONArray friendDataArray = jsonObject.getJSONArray("data3");
for (int i = 0; i < friendDataArray.length(); i++)
String image = friendDataArray.getJSONObject(i).getString("getmyUserImage");
viewUserProfile_Wrapper followerData = new viewUserProfile_Wrapper(image);
friendsList.add(followerData);
正如 I_A_Mok 评论的那样，删除 return null from
if (callResult.equals("SUCCESS"))......
【讨论】：
如果我设置 TAG= friends 那么 asynctask 将只设置FriendsRecycler.setAdapter(adapter1); 这个适配器而不是其他适配器。如果我理解错了，请纠正我
对不起，我错过了阅读您的问题。你能填充所有三个 recyclerviews 吗？或者你只有'adapter3'有问题
在您的 setUserVisibleHint 中添加 'getView!=null' 检查，因为它在 onCreateView 之前被调用
在viewpager下一个片段的onCreate call before setUserVisibleHint`以上是关于使用 recyclerview 和 Asynctask 设置 Viewpager的主要内容，如果未能解决你的问题，请参考以下文章
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