Question

我正从我的服务器检索JSON数据，我想用它来更新我的ListView。检索数据一切正常但在完成后它会尝试更新列表我只得到一个没有错误的空白页面。 Log.d("ListLocations", "after")能够运行，所以我没有看到PostExecute和SimpleAdapter的启用有任何问题

我已经调整了本教程中的代码：http://www.androidhive.info/2012/05/how-to-connect-android-with-php-mysql/#ff0000

这是我的ListActivity类：

public class ListLocations extends ListActivity
{
    //Root url and controller
    private static String root = "someURL/";
    private static String locationsController = "locations";

    // Progress Dialog
    private ProgressDialog pDialog;

    //JSON node names for locations 
    private static final String TAG_ID = "id";
    private static final String TAG_NAME = "name";
    private static final String TAG_TERRAIN = "terrain";
    private static final String TAG_DIFFICULTY = "difficulty";
    private static final String TAG_RATINGS = "ratings";
    private static final String TAG_UID = "uid";
    private static final String TAG_LONG= "long";
    private static final String TAG_LAT= "lat";
    private static final String TAG_DISTANCE= "distance";
    private static final String TAG_COMID= "comid";

    //Will be used to contain the list of locations extracted from JSON
    ArrayList<HashMap<String, String>> list = new ArrayList<HashMap<String, String>>();

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_locations);

        new GetLocations().execute(root + locationsController);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_list_locations, menu);
        return true;
    }
    class GetLocations extends AsyncTask<String, Void, Void>
    {
        //      private ProgressDialog pDialog;
        protected void onPreExecute()
        {
            super.onPreExecute();
            pDialog = new ProgressDialog(ListLocations.this);
            pDialog.setMessage("Loading locations. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }


        @Override
        public Void doInBackground(String... urls)
        {
            try
            {               
                JSONHandler jsonHandler = new JSONHandler();
                JSONObject json= jsonHandler.getJSONFromUrl(urls[0]);
                Log.d("ListLocations",json.toString());

                JSONArray locations = json.getJSONArray("locations");
                int length = locations.length();

                ArrayList<HashMap<String, String>> list = new ArrayList<HashMap<String, String>>();
                for(int i = 0; i < length; i++)
                {
                    JSONObject loc = locations.getJSONObject(i);

                    //Create HashMap    
                    HashMap<String, String> map = new HashMap<String, String>();

                    //Get and store values into map
                    map.put("id", loc.getString(TAG_ID));
                    map.put("name", loc.getString(TAG_NAME));
                    map.put("distance", loc.getString(TAG_DISTANCE));
                    map.put("difficulty", loc.getString(TAG_DIFFICULTY));
                    map.put("terrain", loc.getString(TAG_TERRAIN));
                    map.put("ratings", loc.getString(TAG_RATINGS));
                    map.put("long", loc.getString(TAG_LONG));
                    map.put("lat", loc.getString(TAG_LAT));
                    map.put("uid", loc.getString(TAG_UID));
                    map.put("comid", loc.getString(TAG_COMID));

                    //Add map to list
                    list.add(map);
                }
                System.out.println(list);

            }
            catch (Exception e)
            {
                 e.printStackTrace();            
            }
            Log.d("ListLocations", "Successfully finished HTTP Request");
            return(null);
        }

          /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(Void result) { 
            super.onPostExecute(result);
            pDialog.dismiss();

            // updating UI from Background Thread
            runOnUiThread(new Runnable() {
                public void run() {
                    Log.d("ListLocations", "inside run");
                       ListAdapter adapter = new SimpleAdapter(
                               ListLocations.this, list,
                               R.layout.list_item, new String[] { TAG_ID,
                                       TAG_NAME},
                               new int[] { R.id.id, R.id.name });



                       Log.d("ListLocations", "after");
                       // updating listview
                       setListAdapter(adapter);


                }
            });

        }

    }
}

这是list_item.xml：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <!-- location id (pid) - will be HIDDEN - used to pass to other activity -->
    <TextView
        android:id="@+id/id"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:visibility="gone" />

    <!-- Name Label -->
    <TextView
        android:id="@+id/name"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:paddingTop="6dip"
        android:paddingLeft="6dip"
        android:textSize="17dip"
        android:textStyle="bold" />

</LinearLayout>

这是activity_list_locations.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

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

</LinearLayout>

Answer 1

您永远不会将数据放在list的{{1}}字段中，因为Activity方法中的SimpleAdapter变量是list局部变量而不是字段。而不是：

doInBackground

写：

//...
ArrayList<HashMap<String, String>> list = new ArrayList<HashMap<String, String>>();
for(int i = 0; i < length; i++) {
//...

所以你不要制作一个局部变量并将这些元素放在右边的列表中。

为什么我的ListView不能使用SimpleAdapter更新？

1 个答案: