如何加載一個片段數據，當它是可見的用戶和保存數據後加載一次

Question

我用setUserVisibleHint（）方法加載數據，但此方法之前調用oncreateview所以我得到NPE。

我從下面提到的鏈接檢查堆棧溢出的Soloutions。

setUserVisibleHint called before onCreateView in Fragment

setUserVisibleHint with Fragments for android

我想，當片段是對用戶可見的加載數據，我想保留的數據，因爲它是裝載once.It後刷卡下一個片段後，不應該清楚。

請幫我這個。 我完全有5個片段。 在我正在服務器調用片段的onCreateView方法的每個片段中。這裏是一個片段的示例。

package com.geelani.sestoauto.list; 


import android.app.Dialog; 
import android.content.Context; 
import android.content.SharedPreferences; 
import android.os.Bundle; 
import android.preference.PreferenceManager; 
import android.support.design.widget.FloatingActionButton; 
import android.support.v4.app.Fragment; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.ProgressBar; 
import android.widget.Toast; 

import com.example.taha.myapplication.backend.model.pricesApi.model.Prices; 
import com.example.taha.myapplication.backend.model.specsPricesApi.SpecsPricesApi; 
import com.example.taha.myapplication.backend.model.specsPricesApi.model.CollectionResponseSpecsPrices; 
import com.example.taha.myapplication.backend.model.specsPricesApi.model.SpecsPrices; 
import com.geelani.sestoauto.MainActivity; 
import com.geelani.sestoauto.R; 
import com.geelani.sestoauto.async.GenericAsyncTaskList; 
import com.geelani.sestoauto.async.ResponseListener; 
import com.geelani.sestoauto.utils.Constants; 
import com.google.api.client.extensions.android.http.AndroidHttp; 
import com.google.api.client.json.gson.GsonFactory; 

import java.util.ArrayList; 
import java.util.HashMap; 


/** 
* A simple {@link Fragment} subclass that shows a list of featured lists a user can see. 
* Use the {@link SpecsFragment#newInstance} factory method to 
* create an instance of this fragment. 
*/ 
public class SpecsFragment extends Fragment implements ResponseListener { 

    private String title; 
    private String location; 
    private ProgressBar mProgBar; 
    private SpecsAdapter mAdapter; 
    private CollectionResponseSpecsPrices specs; 
    private ArrayList<SpecsPrices> items = new ArrayList(); 
    private ArrayList<Prices> items1 = new ArrayList(); 
    private Context mContext; 
    private ImageView handler; 
    ListView listView; 
    SharedPreferences getPrefs; 
    private boolean isViewShown = false; 


    public SpecsFragment() { 
     /* Required empty public constructor */ 
    } 


    /** 
    * Create fragment and pass bundle with data as it's arguments 
    */ 
    public static SpecsFragment newInstance(String title, String location) { 
     SpecsFragment fragment = new SpecsFragment(); 
     Bundle args = new Bundle(); 
     args.putString(Constants.TITLES, title); 
     args.putString(Constants.LOCATION, location); 
     fragment.setArguments(args); 
     return fragment; 
    } 

    @Override 
    public void setUserVisibleHint(boolean isVisibleToUser) { 
     super.setUserVisibleHint(isVisibleToUser); 
     if (getView() != null) { 
      isViewShown = true; 
      // fetchdata() contains logic to show data when page is selected mostly asynctask to fill the data 
      listSpecs(); 
     } else { 
      isViewShown = false; 
     } 
    } 

    /** 
    * Initialize instance variables with data from bundle 
    */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     if (getArguments() != null) { 
      title = getArguments().getString(Constants.TITLES); 
      location = getArguments().getString(Constants.LOCATION); 
      //  Log.d("location",location.toString()); 
      if (!isViewShown) { 
       listSpecs(); 
      } 

     } 

    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     mContext = getContext(); 
     View mView = inflater.inflate(R.layout.fragment_specifications, container, false); 
     getPrefs = PreferenceManager 
       .getDefaultSharedPreferences(mContext); 
     if (getPrefs.getString(Constants.CITY, null) == null) { 

      searchCitiesList(); 

     } 
     RecyclerView mRecy = (RecyclerView) mView.findViewById(R.id.rv_ff); 
     mProgBar = (ProgressBar) mView.findViewById(R.id.prog_bar_ff); 
     handler = (ImageView) mView.findViewById(R.id.handler); 
     mRecy.setLayoutManager(new LinearLayoutManager(getContext())); 


     mAdapter = new SpecsAdapter(mContext); 
     mRecy.setAdapter(mAdapter); 
     listSpecs(); 
     return mView; 
    } 

    private void listSpecs() { 

     mProgBar.setVisibility(View.VISIBLE); 
     SpecsPrices specs = new SpecsPrices(); 
     SpecsPricesApi api = new 
       SpecsPricesApi(AndroidHttp.newCompatibleTransport(), new GsonFactory(), null 
     ); 
     GenericAsyncTaskList<SpecsPricesApi, SpecsPrices, SpecsFragment> asyncTask = new GenericAsyncTaskList<SpecsPricesApi, SpecsPrices, SpecsFragment>(
       api, 
       specs, 
       this, 
       getActivity(), 
       null, 
       title, 
       "make", 
       "basemodel", 
       "Mumbai", 
       Constants.LIST_SPECSPRICES, 
       "false" 
     ); 
     asyncTask.execute(); 

    } 


    public void searchCitiesList() { 
     final Dialog dialog = new Dialog(mContext); 
     dialog.setContentView(R.layout.select_city); 
     dialog.setTitle("Select City"); 
     listView = (ListView) dialog.findViewById(R.id.list1); 

     String[] values = new String[]{"Mumbai", "New Delhi", "Bangalore", "Pune", "Chennai", "Kolkata", "Hyderabad", "Ahmedabad", "Chandigarh", "Gurgaon" 
       , "Noida", "Navi-Mumbai", "Thane", "Cochin", "Faridabad", "Ghaziabad"}; 
     dialog.show(); 
     ArrayAdapter<String> adapter = new ArrayAdapter<String>(mContext, 
       R.layout.listcity, R.id.city1, values); 
     listView.setAdapter(adapter); 
     listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { 

      @Override 
      public void onItemClick(AdapterView<?> parent, View view, 
            int position, long id) { 
       int itemPosition = position; 
       String itemValue = (String) listView 
         .getItemAtPosition(position); 
       SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(mContext); 
       SharedPreferences.Editor editor = settings.edit(); 
       editor.putString(Constants.CITY, itemValue); 
       editor.commit(); 
       // Show Alert 
       Toast.makeText(
         mContext, 
         "selected" + itemValue, Toast.LENGTH_LONG).show(); 
       dialog.cancel(); 

      } 

     }); 
    } 

    /** 
    * Updates the order of mListView onResume to handle sortOrderChanges properly 
    */ 
    @Override 
    public void onResume() { 
     super.onResume(); 


    } 

    /** 
    * Cleanup the adapter when activity is paused. 
    */ 
    @Override 
    public void onPause() { 
     super.onPause(); 
    } 


    @Override 
    public void processlistener(String type, Object result) { 
     if (type.contentEquals(Constants.LIST_SPECSPRICES)) { 
      specs = (CollectionResponseSpecsPrices) result; 
      items = (ArrayList<SpecsPrices>) specs.getItems(); 
      mProgBar.setVisibility(View.GONE); 
      mAdapter.addItems(items, items1, title); 
      //listprices(); 
     } else { 
      handler.setVisibility(View.VISIBLE); 
      mProgBar.setVisibility(View.GONE); 

     } 
    } 
} 

Answer 1

嘗試這樣的：

private boolean _hasLoadedOnce = false; // your boolean field 

    @Override 
    public void setUserVisibleHint(boolean isFragmentVisible_) { 
     super.setUserVisibleHint(true); 

     if (this.isVisible()) { 
      // we check that the fragment is becoming visible 
      if (isFragmentVisible_ && !_hasLoadedOnce) { 
       if (global.isNetworkAvailable()) { 

        listSpecs(); 

       } 
       _hasLoadedOnce = true; 
      } 
     } 
    }