在从服务器检索数据的片段中创建ListView

Question

我一直试图在从服务器获取数据的片段中创建ListView，但迄今为止都不成功。我一直在使用以下网站：Vogella了解如何在片段中实现ListView，但是我在尝试从服务器填充数据时遇到困难。

package com.example.ips_alpha; 

import java.util.ArrayList; 
import java.util.HashMap; 
import android.util.Log; 

import org.json.JSONArray; 
import org.json.JSONException; 
import org.json.JSONObject; 
import android.os.AsyncTask; 
import android.os.Bundle; 
import android.support.v4.app.ListFragment; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ArrayAdapter; 
import android.widget.ListAdapter; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.TableLayout; 

public class Gold_Visitors2 extends ListFragment{ 

//JSON Node names (level, sensorID, value) 
String SPACES = "spaces"; //String array name of php 
String LEVEL = "level"; 
String SENSORID = "sensorID"; 
String VALUE = "value"; 
//pspace JSONArray 
JSONArray pspace = null; 
String[] levels = new String[]{LEVEL, SENSORID, VALUE}; 

int [] ids = new int[]{}; 

private static String url = "http://www.example.com/getUsers12.php"; 


public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    View view = inflater.inflate(R.layout.fragment_gold_visitors, null); 


    new MyAsyncTask().execute(); 
    return view; 

} 

class MyAsyncTask extends AsyncTask<String, Integer, ArrayList<HashMap<String, String>> > { 


    //Hashmap for ListView 
    ArrayList<HashMap<String, String>> levelList = new ArrayList<HashMap<String, String>>(); 

    @Override 
    protected ArrayList<HashMap<String, String>>doInBackground(String... params) { 

//Creating JSON Parser instance 
     JSONParser jParser = new JSONParser(); 

     //getting JSON string from URL 

     JSONObject json = jParser.getJSONFromUrl(url); 

     try { 
      //Getting Array of spaces 
      pspace = json.getJSONArray(SPACES); 

      //looping through all spaces 
      for(int i = 0; i < pspace.length(); i++){ 
       JSONObject p = pspace.getJSONObject(i); 

      //Storing each json item in variable 
       String level = p.getString(LEVEL); 
       String sensorID = p.getString(SENSORID); 
       String value = p.getString(VALUE); 
      //creating new HashMap 

       HashMap<String, String> map = new HashMap <String, String>(); 
      //adding each child node to HashMap Key => 
       map.put(LEVEL, level); 
       map.put(SENSORID, sensorID); 
       map.put(VALUE, value); 

      //adding HashList to ArrayList 
      } 
     }catch(JSONException e){ 
      e.printStackTrace(); 

     } 
     return levelList; 

    } 

    @Override 
    protected void onPostExecute(ArrayList<HashMap<String, String>> levelList) { 

     ListAdapter adapter = new SimpleAdapter(getActivity(), levelList, R.layout.fragment_gold_visitors, levels, ids); 
     setListAdapter(adapter); 


    } 


} 
} 

以下是布局文件：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:orientation="vertical" > 

<ListView 
    android:id="@id/android:list" 
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" > 
</ListView> 

目前我的应用程序被编译并不会崩溃，但访问是应该显示ListView的片段时，它是空白。我相信我搞乱了ASyncTask和适配器，任何帮助将不胜感激。

Answer 1

您在doInBackground中返回levelList，但您从未从检索到的JSON中为其添加任何项目。你只有一个空的ArrayList，所以ListView是空的。