java - 为什么gridview不显示任何项目？仅在恢复 Activity 后才显示

Question

我将项目添加到 ArrayList，然后将其添加到适配器。这是我的适配器

public class LazyAdapterInventory extends BaseAdapter {

    private Activity activity;
    private ArrayList<HashMap<String, String>> data;
    private  LayoutInflater inflater=null;

    public LazyAdapterInventory(Activity a, ArrayList<HashMap<String, String>> d) {
          activity = a;
          data=d;
          inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
          imageLoader=new ImageLoader(activity.getApplicationContext());

    }

    public int getCount() {
        return data.size();
    }

    public void clearCache() {
        imageLoader.clearCache();
    }


    public Object getItem(int position) {
        return data.get(position);
    }


    public long getItemId(int position) {
        return position;
    }

    public View getView(final int position, final View convertView, ViewGroup parent) {
        View vi=convertView;
        if(convertView==null)
            vi = inflater.inflate(R.layout.item_list_all, null);

        final TextView title = (TextView)vi.findViewById(R.id.title); // title


         HashMap<String, String> song = new HashMap<String, String>();
        song = data.get(position);

        title.setText(convertFromUTF8(song.get("key_title")));

        return vi;
    }


}

这是我的主要 Activity

 public class UserInfoActivity extends SherlockActivity {
        ArrayList<HashMap<String, String>> friendsList = new ArrayList<HashMap<String, String>>();
        LazyAdapterInventory friendsadapter;
        private GridView friendslist;

    protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_user_info);

                friendsadapter=new LazyAdapterInventory(this, friendsList);  

                friendslist=(GridView)findViewById(R.id.friends_list);

                friendslist.setAdapter(friendsadapter);

                GetInfoList().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);

            }



        }

这里是获取

class GetInfoList extends AsyncTask<String, String, String> {

  protected String doInBackground(String... args) {

        JSONObject json = jParser.makeHttpRequest(URL, "GET", param);
       JSONObject friendslist = json.getJSONObject("friendslist");
   JSONArray friends = friendslist.getJSONArray("friends");
        for (int i =0;i<friends.length();i++){
             JSONObject friend = friends.getJSONObject(i);
             HashMap<String, String> map = new HashMap<String, String>();
                map.put("key_title", friend.getString("steamid"));
            friendsList.add(map);
                 }
        return null;
            }
  protected void onPostExecute(String file_url) 
            {
             friendsadapter.notifyDataSetChanged();
             }
    }

回复:

{
    "friendslist": {
        "friends": [
            {
                "steamid": "76561197966153504",
                "relationship": "friend",
                "friend_since": 1395491684
            },
            {
                "steamid": "76561198002475521",
                "relationship": "friend",
                "friend_since": 1393012575
            },
            {
                "steamid": "76561198034678588",
                "relationship": "friend",
                "friend_since": 1395407339
            },
            {
                "steamid": "76561198040519811",
                "relationship": "friend",
                "friend_since": 1395688168
            },
            {
                "steamid": "76561198052749663",
                "relationship": "friend",
                "friend_since": 1395997768
            },
            {
                "steamid": "76561198060262946",
                "relationship": "friend",
                "friend_since": 1360606275
            },
            {
                "steamid": "76561198068379313",
                "relationship": "friend",
                "friend_since": 1395068101
            },
            {
                "steamid": "76561198073896175",
                "relationship": "friend",
                "friend_since": 1394910978
            },
            {
                "steamid": "76561198074813543",
                "relationship": "friend",
                "friend_since": 1394523426
            },
            {
                "steamid": "76561198081103330",
                "relationship": "friend",
                "friend_since": 1395810398
            },
            {
                "steamid": "76561198082945313",
                "relationship": "friend",
                "friend_since": 1394913814
            },
            {
                "steamid": "76561198084403469",
                "relationship": "friend",
                "friend_since": 1393667423
            },
            {
                "steamid": "76561198092220408",
                "relationship": "friend",
                "friend_since": 1394910366
            },
            {
                "steamid": "76561198092249389",
                "relationship": "friend",
                "friend_since": 1395447861
            },
            {
                "steamid": "76561198096843914",
                "relationship": "friend",
                "friend_since": 1373139292
            },
            {
                "steamid": "76561198099008433",
                "relationship": "friend",
                "friend_since": 1395810393
            },
            {
                "steamid": "76561198109190777",
                "relationship": "friend",
                "friend_since": 1394211966
            },
            {
                "steamid": "76561198112623128",
                "relationship": "friend",
                "friend_since": 1395810497
            },
            {
                "steamid": "76561198112677589",
                "relationship": "friend",
                "friend_since": 1395395453
            },
            {
                "steamid": "76561198112762255",
                "relationship": "friend",
                "friend_since": 1395429304
            },
            {
                "steamid": "76561198114529800",
                "relationship": "friend",
                "friend_since": 1395423621
            },
            {
                "steamid": "76561198115955698",
                "relationship": "friend",
                "friend_since": 1395429444
            },
            {
                "steamid": "76561198118605481",
                "relationship": "friend",
                "friend_since": 1393187401
            },
            {
                "steamid": "76561198119746587",
                "relationship": "friend",
                "friend_since": 1395397411
            },
            {
                "steamid": "76561198121134047",
                "relationship": "friend",
                "friend_since": 1395810452
            },
            {
                "steamid": "76561198121560711",
                "relationship": "friend",
                "friend_since": 1395997769
            },
            {
                "steamid": "76561198122678853",
                "relationship": "friend",
                "friend_since": 1389529761
            },
            {
                "steamid": "76561198123336629",
                "relationship": "friend",
                "friend_since": 1393012567
            }
        ]

    }
}

打开 Activity LIST 后为空...但 ArrayList>friendsList 不为空。如果我最小化然后最大化应用程序列表已满。问题出在哪里？

Answer 1

在 onPostExecute() 方法中设置您的适配器。

 protected void onPostExecute(String file_url) 
        {
         friendsadapter=new LazyAdapterInventory(this, friendsList);  
         friendslist.setAdapter(friendsadapter);
         friendsadapter.notifyDataSetChanged();
         }
 }

也删除这个

    friendsadapter=new LazyAdapterInventory(this, friendsList);  
    friendslist.setAdapter(friendsadapter);

来自 onCreate()。

这是因为您可以在 onPostExecute() 方法中更新您的 UI 元素。

更新:

还在 onCreate() 方法之前为您的 ArrayList 声明全局变量。

  ArrayList<HashMap<String, String>> friendsList;

并在 onCreate() 方法上执行 AsyncTask 之前对其进行初始化。

 friendsList = new ArrayList<HashMap<String, String>>();

在此更改

        for (int i =0;i<friends.length();i++){
          JSONObject friend = friends.getJSONObject(i);
          HashMap<String, String> map = new HashMap<String, String>();
          map.put("steamid", friend.getString("steamid"));
          map.put("relationship", friend.getString("relationship"));
          map.put("friend_since", friend.getString("friend_since"));
        friendsList.add(map);