Question

我有一个从JSON中检索对象的活动。第一次显示活动时，一切正常。

但是如果用户前进并后退并再次打开它，则会显示任何数据。

这是我的代码：

package com.solinpromex.casajuventudtrescantos;

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

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;

public class DondeEsta_T1_MainActivity extends Activity {
    // Declare Variables

     private static final String TAG_NAME = "nombreCategoria";
        private static final String TAG_ID = "idPrueba";
        private String name = "Categoria";
        private String id = "id";
    JSONObject jsonobject;
    JSONArray jsonarray;
    ListView listview;
    DondeEsta_T1_ListViewAdapter adapter;
    ProgressDialog mProgressDialog;
    ArrayList<HashMap<String, String>> arraylist;
    static String ID_DES= "id_des";
    static String TITULO_DES = "titulo_des";
    static String CATEGORIAS_DES = "categoria_des";
    static String LUGAR_DES = "lugar_des";
    static String LATITUD_DES = "latitud_des";
    static String LONGITUD_DES = "longitud_des";
    static String IMAGEN_DES = "imagen_des";
    static String DESCRIPCION_DES = "descripcion_des";
    static String WEB_DES = "web_des";
    static String MAIL_DES = "mail_des";
    static String TEL_DES = "tel_des";
    static String LUGAR_CORTO = "lugar_corto";
    static String idPrueba = "idPrueba";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.v("MVASCO", "context is null!");
         // getting intent data
        Intent in = getIntent();

     // Get JSON values from previous intent
       name = in.getStringExtra(TAG_NAME);
       id = in.getStringExtra(TAG_ID);
       idPrueba =in.getStringExtra(idPrueba);

        setContentView(R.layout.dondeesta_t1_listview_main);
        // Execute DownloadJSON AsyncTask
        //new DownloadJSON().execute();
    }

    // DownloadJSON AsyncTask
    private class DownloadJSON extends AsyncTask<Void, Void, Void> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            // Create a progressdialog

        }

        @Override
        protected Void doInBackground(Void... params) {
            // Create an array


        //  Log.v("categoria para pasar a la URL", id_categoria_donde_esta);
            arraylist = new ArrayList<HashMap<String, String>>();
            // Retrieve JSON Objects from the given URL address

            jsonobject = JSONfunctions
                    .getJSONfromURL("http://.hidden url.../app_php_files/recuperar_categorias_donde_esta_t1.php?cat="+idPrueba);

            try {
                // Locate the array name in JSON
                jsonarray = jsonobject.getJSONArray("Categorias");

                for (int i = 0; i < jsonarray.length(); i++) {
                    HashMap<String, String> map = new HashMap<String, String>();
                    jsonobject = jsonarray.getJSONObject(i);
                    // Retrive JSON Objects
                    map.put("id_des", jsonobject.getString("id_des"));
                    map.put("titulo_des", jsonobject.getString("titulo_des"));

                    map.put("categoria_des", jsonobject.getString("categoria_des"));
                    map.put("lugar_des", jsonobject.getString("lugar_des"));
                    map.put("latitud_des", jsonobject.getString("latitud_des"));
                    map.put("longitud_des", jsonobject.getString("longitud_des"));
                    map.put("descripcion_des", jsonobject.getString("descripcion_des"));
                    map.put("web_des", jsonobject.getString("web_des"));
                    map.put("mail_des", jsonobject.getString("mail_des"));
                    map.put("imagen_des", "http://www.solinpromex.com/casajuventud/sitios/"+jsonobject.getString("imagen_des"));                    
                    map.put("tel_des", jsonobject.getString("tel_des"));
                    map.put("lugar_corto", jsonobject.getString("lugar_corto"));
                    // Set the JSON Objects into the array
                    arraylist.add(map);
                }
            } catch (JSONException e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void args) {
            // Locate the listview in listview_main.xml
            listview = (ListView) findViewById(R.id.listview);
            // Pass the results into ListViewAdapter.java
            adapter = new DondeEsta_T1_ListViewAdapter(DondeEsta_T1_MainActivity.this, arraylist);
            // Set the adapter to the ListView
            listview.setAdapter(adapter);


        }
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub
        super.onResume();

        new DownloadJSON().execute();
    }

}

我做错了什么？

Answer 1

把这个

   Intent in = getIntent();

 // Get JSON values from previous intent
   name = in.getStringExtra(TAG_NAME);
   id = in.getStringExtra(TAG_ID);
   idPrueba =in.getStringExtra(idPrueba);

进入方法onResume然后它应该工作我认为

另请参阅此活动生命周期概述 http://www.android-app-market.com/wp-content/uploads/2012/03/Android-Activity-Lifecycle.png

第二次打开活动时未显示JSON数据

1 个答案: