如何通过 JSON 获取实时更新到 listview

Question

我找不到通过 JSON 获取列表视图的实时更新的方法。

我的活动是从网页请求 JSON 数据，代码是：

public class Second extends Activity {

    static final String Li_nk = "LinkName:";
    static final String Image_name = "ImageName:";
    ListView list;
    public final static String AUTH = "authentication";
    static final String KEY_THUMB_URL = "thumb_image"; // Uri.decode("http://zeesms.info/android_app_images/Koala.jpg");

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Intent i2 = getIntent();
        String wrd = i2.getStringExtra("entrd");
        Log.v("keyis", wrd);

        // if(wrd.equalsIgnoreCase("test")){
        JSONObject j2 = JSONfunctions.getJSONfromURL("/webservice_search.php?keyword=" + wrd + "&format=json");

        ArrayList<HashMap<String, String>> mylist = new ArrayList<HashMap<String, String>>();
        try {
            JSONArray jray = j2.getJSONArray("listings");
            for (int i = 0; i < jray.length(); i++) {
                Log.v("state", "json data being read");
                JSONObject j3 = jray.getJSONObject(i);
                String first = j3.getString("listing");
                Log.v("sublist", first);
                JSONObject j4 = j3.getJSONObject("listing");
                String sec = j4.getString("links");

                int maxLength = (sec.length() < 30) ? sec.length() : 27;
                sec.substring(0, maxLength);
                String cutsec = sec.substring(0, maxLength);
                Log.v("links are", cutsec);
                String img = j4.getString("image_name");
                Log.v("image name is ", img);
                // Uri
                // dimg=Uri.parse("http://zeesms.info/android_app_images/Koala.jpg");
                HashMap<String, String> map = new HashMap<String, String>();

                map.put("Id", String.valueOf(i));
                map.put(Li_nk, cutsec);
                map.put(Image_name, j4.getString("image_name"));

                map.put(KEY_THUMB_URL, "http://zeesms.info/android_app_images/" + img);
                mylist.add(map);

            }

        }
        catch (JSONException e) {
            alertbox();
            Log.e("loG_tag", "Error parsing" + e.toString());
        }

        list = (ListView) findViewById(R.id.lv1);
        this.list.setEmptyView(findViewById(R.id.empty));
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                // Toast.makeText(getApplicationContext(),"Click ListItem Number "
                // + position, Toast.LENGTH_LONG).show();
                Intent myIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.riffre.com/"));
                startActivity(myIntent);
            }

        });
        LazyAdapter adapter = new LazyAdapter(this, mylist);

        list.setAdapter(adapter);
        list.setItemsCanFocus(false);

        // }
        /*
         * else{ alertbox(); }
         */

    }

    /*
     * public void register(View view) { Log.w("C2DM",
     * "start registration process"); Intent intent = new
     * Intent("com.google.android.c2dm.intent.REGISTER");
     * intent.putExtra("app", PendingIntent.getBroadcast(this, 0, new
     * Intent(), 0)); // Sender currently not used intent.putExtra("sender",
     * "nonsenses@gmail.com"); startService(intent); }
     * 
     * public void showRegistrationId(View view) { SharedPreferences prefs =
     * PreferenceManager .getDefaultSharedPreferences(this); String string =
     * prefs.getString(AUTH, "n/a"); Toast.makeText(this, string,
     * Toast.LENGTH_LONG).show(); Log.d("C2DM RegId", string);
     * 
     * }
     */
    public void alertbox() {

        new AlertDialog.Builder(this).setMessage("Invalid Keyword,No Results found").setTitle("Alert").setCancelable(true).setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {

            public void onClick(DialogInterface dialog, int whichButton) {

                finish();

            }
        }).show();
    }
}

我正在使用自定义适配器，代码如下：

public class LazyAdapter extends BaseAdapter {
    private Activity activity;
    private ArrayList<HashMap<String, String>> data;
    private static LayoutInflater inflater=null;
    public ImageLoader imageLoader; 


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

    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return data.size();
    }

    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }


    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View vi=convertView;
        if(convertView==null)

            vi = inflater.inflate(R.layout.custom_row_view1, null);

        TextView title = (TextView)vi.findViewById(R.id.linkname); // merchnts name
        TextView artist = (TextView)vi.findViewById(R.id.imagename); // address
        //TextView duration = (TextView)vi.findViewById(R.id); // distance
       ImageView thumb_image=(ImageView)vi.findViewById(R.id.mClogo); // logo

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

        // Setting all values in listview
       title.setText(jsn.get(Second.Li_nk));
       artist.setText(jsn.get(Second.Image_name));
        //duration.setText(song.get(CustomizedListView.KEY_DURATION));
        imageLoader.DisplayImage(jsn.get(Second.KEY_THUMB_URL), thumb_image);
        return vi;
    }
}

我想要的是应用程序每分钟左右用数据更新列表视图。列表中的最新条目也应位于顶部。

最好的方法是什么？

Answer 1

将您的 JSON 解析代码（可能是您的 try..catch 块）放在单独的函数中，而不是放在 onCreate() 中。

因此可以轻松地每分钟调用该部分。假设函数名称LoadData() 还添加了一行adapter.notifyDataSetChanged() 以每次更新适配器/列表。

现在在您的 onCreate() 中，编写此代码以每隔一分钟调用一次该函数，

    final Handler handler = new Handler();
    Runnable runable = new Runnable() {

        @Override
        public void run() {

            //call the function
            LoadData();
            //also call the same runnable
            handler.postDelayed(this, 1000);
        }
    };
    handler.postDelayed(runable, 1000);

现在第二个问题，在顶部添加新数据..

我现在只想写一个循环，在调用适配器通知更改之前将其添加到您的函数中，例如

     ArrayList<HashMap<String,String>> mylist = new  ArrayList<HashMap<String,String>>(); 
     ArrayList<HashMap<String,String>> mylistTemp = new  ArrayList<HashMap<String,String>>();
     for(int i = mylist.size()-1 ; i >=0;i--)
     {
         mylistTemp.add(mylist.get(i));
     }
     mylist = mylistTemp;

Answer 2

如果您上面的代码可以正常工作，您应该可以通过以下步骤实现您的目标：

• 将您的 JSON 加载代码提取到 AsyncTask 中，您可以每分钟触发一次。 (AsyncTask)
• 使用 AsyncTask 更新您的 ListAdapter。

Answer 3

这是 onCreate() 方法的一个可能实现，它将每分钟运行一次更新任务：

public class JSON_AndroidActivity extends Activity {
    /** Called when the activity is first created. */
    private JSONLoaderTask mJSONLoaderTask;
    private Handler mHandler;
    private ArrayAdapter<String> mArrayAdapter;
    private Runnable mRefresher = new Runnable() {

        @Override
        public void run() {
            mJSONLoaderTask = new JSONLoaderTask(JSON_AndroidActivity.this, mArrayAdapter);
            mJSONLoaderTask.execute("");
            mHandler.postDelayed(this, 1000);

        }
    };
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mHandler.postDelayed(mRefresher, 1000);
    }
}

这是一个可能任务的外壳实现，您可以在其中执行繁重的负载并更新列表的适配器：

public class JSONLoaderTask extends AsyncTask<String, String, String> {
    private Context context;
    private ProgressDialog progressDialog;
    private final ArrayAdapter<String> mArrayAdapter;

    public JSONLoaderTask(Context pContext, ArrayAdapter<String> pArrayAdapter) {
        this.context = pContext;
        this.mArrayAdapter = pArrayAdapter;
    }

    @Override
    protected void onPreExecute() {
        progressDialog = new ProgressDialog(context);
        progressDialog.show();
    }

    @Override
    protected String doInBackground(String... params) {
         String result = getJSONStream();
        return result;
    }

    private String getJSONStream() {
        //load your string here
        return "";
    }

    @Override
    protected void onPostExecute(String result) {
        progressDialog.dismiss();
        // Update your ArrayAdapter
    }

}