Question

在我的带有外部适配器的活动（列表视图）中，当用户从另一个活动返回活动时，我需要刷新数据：

这是我目前的代码：

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

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 Empresas_MainActivity extends Activity {
    // Declare Variables

     private static final String TAG_NAME = "nombreCategoria";
        private static final String TAG_ID = "idCategoria";
        private String name = "Categoria";
        private String id = "id";
    JSONObject jsonobject;
    JSONArray jsonarray;
    ListView listview;
    Empresas_ListViewAdapter adapter;
    ProgressDialog mProgressDialog;
    ArrayList<HashMap<String, String>> arraylist;
    static String VALORACIONEMPRESA = "valoracionEmpresa";
    static String NOMBREEMPRESA = "nombreEmpresa";
    static String DIRECCIONEMPRESA = "direccionEmpresa";
    static String STRIMAGEN = "strImagen";
    static String DESCRIPCIONEMPRESA = "descripcionEmpresa";
    static String TELEFONOEMPRESA = "telefonoEmpresa";
    static String FACEBOOKEMPRESA = "facebookEmpresa";
    static String EMAILEMPRESA = "emailEmpresa";
    static String TEXTOOFERTA = "textoOferta";
    static String HORARIOEMPRESA = "horarioEmpresa";
    static String LATITUDEMPRESA = "latitudEmpresa";
    static String LONGITUDEMPRESA = "longitudEmpresa";
    static String IDEMPRESA = "idEmpresa";



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


        // Get JSON values from previous intent
       name = in.getStringExtra(TAG_NAME);
       id = in.getStringExtra(TAG_ID);
        this.setTitle(name);
        // Get the view from listview_main.xml
        setContentView(R.layout.empresas_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
            mProgressDialog = new ProgressDialog(Empresas_MainActivity.this);
            // Set progressdialog title
            mProgressDialog.setTitle("Vive Gran Canaria");
            // Set progressdialog message
            mProgressDialog.setMessage(name);
            mProgressDialog.setIndeterminate(false);
            // Show progressdialog
            mProgressDialog.show();
        }

        @Override
        protected Void doInBackground(Void... params) {
            // Create an array
            arraylist = new ArrayList<HashMap<String, String>>();
            // Retrieve JSON Objects from the given URL address
            jsonobject = JSONfunctions
                    .getJSONfromURL("http://xxxxxx/android_ofertaslist_todas.php?id="+id);

            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("valoracionEmpresa", jsonobject.getString("valoracionEmpresa"));
                    map.put("nombreEmpresa", jsonobject.getString("nombreEmpresa"));
                    map.put("direccionEmpresa", jsonobject.getString("direccionEmpresa"));
                    map.put("strImagen", jsonobject.getString("strImagen"));
                    map.put("descripcionEmpresa", jsonobject.getString("descripcionEmpresa"));
                    map.put("telefonoEmpresa", jsonobject.getString("telefonoEmpresa"));
                    map.put("emailEmpresa", jsonobject.getString("emailEmpresa"));
                    map.put("textoOferta", jsonobject.getString("textoOferta"));
                    map.put("horarioEmpresa", jsonobject.getString("horarioEmpresa"));
                    map.put("facebookEmpresa", jsonobject.getString("facebookEmpresa"));
                    map.put("latitudEmpresa", jsonobject.getString("latitudEmpresa"));
                    map.put("longitudEmpresa", jsonobject.getString("longitudEmpresa"));
                    map.put("idEmpresa", jsonobject.getString("idEmpresa"));


                    // 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 Empresas_ListViewAdapter(Empresas_MainActivity.this, arraylist);
            // Set the adapter to the ListView
            listview.setAdapter(adapter);
            adapter.notifyDataSetChanged();
            // Close the progressdialog
            mProgressDialog.dismiss();
        }
    }
}

我已经在postOnExecute方法中调用了adapter.notifyDataSetChanged（），但是当从其他某些值可能已更改的活动返回时，这些值不会更新。我应该在哪里或如何使用adapter.notifyDataSetChanged（）;

谢谢。

Answer 1

您必须使用onResume。这两个函数都是在后退时调用的，当活动是第一次启动时。

所以你应该移动以下内容：

new DownloadJSON().execute();

到

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onPause();
    new DownloadJSON().execute();
}

在这种情况下，您无需包含notifyDataSetChanged()。我希望它可以帮助你

Answer 2

 adapter = new Empresas_ListViewAdapter(Empresas_MainActivity.this, arraylist);

此处您必须通知您的适配器有关数据更改。

       adapter.notifyDataSetChanged();
        // first you have to  notify adapter then Set the adapter to the ListView
        listview.setAdapter(adapter);

根据我的意见，

其余的代码也没问题。

adapter.notifyDataSetChanged（）在活动代码中的位置

2 个答案: