ListFragment不显示列表中的数据

Question

因此，我之前问过这个问题，但在尝试打开导航抽屉并转到其他选项卡然后返回之后，它不再工作。它不再在列表中显示数据。先谢谢了！

主要活动

package com.goldleaf.branden.goldleafcomics; 

import android.os.Bundle; 
import android.support.design.widget.NavigationView; 
import android.support.v4.view.GravityCompat; 
import android.support.v4.widget.DrawerLayout; 
import android.support.v7.app.ActionBarDrawerToggle; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.MenuItem; 
import android.widget.ListView; 
import android.widget.Toast; 

import com.kosalgeek.android.json.JsonConverter; 
import com.kosalgeek.genasync12.AsyncResponse; 
import com.kosalgeek.genasync12.PostResponseAsyncTask; 


import java.util.ArrayList; 
import java.util.List; 

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener{ 
    ListView lvGlimpse; 
    public List<UniverseListing>universalListings = new ArrayList<UniverseListing>(); 
    final GlimpseListFragment glimpse = new GlimpseListFragment(); 

    NavigationView navigationView; 
    Toolbar toolbar; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     String url = "http://goldleafcomics.com/application/UniverseGlimpse.JSON"; 
     PostResponseAsyncTask task = new PostResponseAsyncTask(MainActivity.this, new AsyncResponse() { 
      @Override 
      public void processFinish(String s) { 
       universalListings = new JsonConverter<UniverseListing>().toArrayList(s, UniverseListing.class); 
       Toast.makeText(MainActivity.this, "Application Data Refreshed", Toast.LENGTH_LONG).show(); 
      } 
     }); 
     task.execute(url); 

     android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction(); 
     fragmentTransaction.replace(R.id.fragment_container, glimpse); 
     fragmentTransaction.commit(); 

     toolbar = (Toolbar) findViewById(R.id.toolbar); 
     setSupportActionBar(toolbar); 
     getSupportActionBar().setTitle("Glimpse"); 

     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
     ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close); 
     drawer.setDrawerListener(toggle); 
     toggle.syncState(); 

     navigationView = (NavigationView) findViewById(R.id.nav_view); 
     navigationView.setNavigationItemSelectedListener(this); 
    } 

    @Override 
    public void onBackPressed() { 
     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
     if (drawer.isDrawerOpen(GravityCompat.START)) { 
      drawer.closeDrawer(GravityCompat.START); 
     } else { 
      super.onBackPressed(); 
     } 
    } 

    @SuppressWarnings("StatementWithEmptyBody") 
    @Override 
    public boolean onNavigationItemSelected(MenuItem item) { 
     // Handle navigation view item clicks here. 
     int id = item.getItemId(); 

     if (id == R.id.nav_news) { 
      getSupportActionBar().setTitle("G.C. News"); 
     } else if (id == R.id.nav_team) { 
      TeamFeedFragment fragment = new TeamFeedFragment(); 
      android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction(); 
      fragmentTransaction.replace(R.id.fragment_container, fragment); 
      getSupportActionBar().setTitle("Team Feed"); 
      fragmentTransaction.commit(); 
     }else if(id == R.id.nav_notifications){ 
      getSupportActionBar().setTitle("Notifications"); 
     }else if(id == R.id.nav_comics){ 
      getSupportActionBar().setTitle("Comics"); 
     }else if(id == R.id.nav_glimpse){ 
      android.support.v4.app.FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction(); 
      fragmentTransaction.replace(R.id.fragment_container, glimpse); 
      getSupportActionBar().setTitle("Glimpse"); 
      fragmentTransaction.commit(); 
     } 
     DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout); 
     drawer.closeDrawer(GravityCompat.START); 
     return true; 
    } 
} 

UniverseListing

package com.goldleaf.branden.goldleafcomics; 

import com.google.gson.annotations.SerializedName; 

public class UniverseListing { 
    @SerializedName("universe_id") 
    public String universeId; 

    @SerializedName("universe_glimpse") 
    public String universeGlimpse; 

    @SerializedName("universe_url") 
    public String universeuRL; 

} 

掠影名单片段

package com.goldleaf.branden.goldleafcomics; 

import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v4.app.ListFragment; 
import android.util.Log; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.AdapterView; 
import android.widget.ArrayAdapter; 
import android.widget.ListView; 
import android.widget.TextView; 
import android.widget.Toast; 

import com.kosalgeek.android.json.JsonConverter; 
import com.kosalgeek.genasync12.*; 

import java.io.FileInputStream; 
import java.util.ArrayList; 
import java.util.List; 

public class GlimpseListFragment extends ListFragment { 
    List<UniverseListing> universalListings = new ArrayList<UniverseListing>(); 
    List<String> glimpse = new ArrayList<String>(); 
    List<String> titles = new ArrayList<String>(); 

    public GlimpseListFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 

     ViewGroup rootView = (ViewGroup)inflater.inflate(R.layout.fragment_glimpse_list, container, false); 

     return rootView; 
    } 

    @Override 
    public void onCreate(@Nullable Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     MainActivity act = new MainActivity(); 

     universalListings = act.universalListings; 

     ArrayList<String> glimpse = new ArrayList<String>(); 
     for(UniverseListing value: universalListings){ 
      glimpse.add(value.universeGlimpse); 
     } 

     ArrayList<String> titles = new ArrayList<String>(); 
     for(UniverseListing value: universalListings){ 
      titles.add(value.universeId); 
     } 

     ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, titles); 
     setListAdapter(adapter); 
    } 

    @Override 
    public void onListItemClick(ListView l, View v, int position, long id) { 
     super.onListItemClick(l, v, position, id); 
     String value = (String)getListAdapter().getItem(position); 
     Toast.makeText(getActivity(), value, Toast.LENGTH_LONG).show(); 
    } 
} 

Answer 1

您创建不是由Android的生命周期管理的活动实例，因此该ArrayList你想要使用的是空的，因为它从来没有填充在行为的onCreate方法中ivity。

MainActivity act = new MainActivity(); 

    universalListings = act.universalListings; // size = 0 

伴随着的是，你有一些异步代码去取你的数据，所以分片甚至可能不会得到你的FragmentTransaction完成时下载列表。

你必须到ArrayList传递到从片段适配器在processFinish方法你有，或调用的AsyncTask代码的片段内，并从processFinish方法内部填充适配器