ListView不显示JSON数据

Question

I am creating a android app using web services, In which giving the place name will search the postal code and display in ListView. But my ListView is not displaying the JSON data from the server. Please advice..

MainActivity.java `

public class MainActivity extends AppCompatActivity {
    private EditText etSearch;
    private ListView lv;
    private ProgressDialog progressDialog;

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

        etSearch = (EditText) findViewById(R.id.editText);
        lv = (ListView) findViewById(R.id.listView);
    }

    public void onClick(View view){
        String place = etSearch.getText().toString();
        if(place.length()>0){
            progressDialog = ProgressDialog.show(MainActivity.this,"Postal Code Search","Please Wait");
            SearchTask task = new SearchTask();
            task.execute(place);
        }else {
            Toast.makeText(this,"Please enter place Name",Toast.LENGTH_LONG).show();
        }
    }
    private ArrayList<String> searchResult = new ArrayList<>();

    private class SearchTask extends AsyncTask<String,Void,JSONObject>{

        @Override
        protected JSONObject doInBackground(String... params) {
            JSONObject result = null;
            String placeName = params[0];

            try {
                String urlS = "http://api.geonames.org/postalCodeSearchJSON?placename="
                        + URLEncoder.encode(placeName, "UTF-8")
                        + "&maxRows=10&username=USERNAME";

                URL url = new URL(urlS);
                HttpURLConnection connection = (HttpURLConnection) url.openConnection();
                connection.setReadTimeout(15000);
                connection.setConnectTimeout(15000);
                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String resp = reader.readLine();
                Log.d("result",resp);
                result = new JSONObject(resp);
            } catch (Exception e){
                Log.e("SearchTask", "Error:"+e.getMessage());
            }
            return result;
        }

        @Override
        protected void onPostExecute(JSONObject response) {
            progressDialog.cancel();
            searchResult.clear();
            if(response != null){
                try{
                    JSONArray postalCodes = response.getJSONArray("postalCodes");
                    for (int i=0;i<postalCodes.length();i++){
                        JSONObject obj = postalCodes.getJSONObject(i);
                        String postalCode = obj.getString("postalCode");
                        String placeName = obj.getString("placeName");
                        searchResult.add("PlaceName: "+placeName+"\nPostalCode: "+postalCode);
                    }
                    if(searchResult.isEmpty()){
                        searchResult.add("No postal code Found");
                        ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_list_item_1,searchResult);
                        lv.setAdapter(adapter);
                        adapter.notifyDataSetChanged();
                    }
                } catch (JSONException je){
                    Toast.makeText(MainActivity.this,"Parsing Error:"+je.getMessage(),Toast.LENGTH_LONG).show();
                }
            } else {
                Toast.makeText(MainActivity.this,"Couldn't Find",Toast.LENGTH_LONG).show();
            }

        }
    }

}
`

This is the UI part. Activity.xml

    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.priya.geocodeapp.MainActivity"

    android:weightSum="1">

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.25"
        android:text="Search Postal Code "
        android:textAlignment="center"
        android:textColor="@android:color/holo_blue_bright"
        android:textSize="14sp"
        android:textStyle="bold"
        android:typeface="sans" />

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.07"
        android:ems="10"
        android:hint="Enter Place Name"
        android:inputType="textPersonName"
        android:textSize="14sp"
        android:layout_marginTop="29dp"
        android:layout_below="@+id/textView"
        android:layout_alignParentEnd="true" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_weight="0.05"
        android:gravity="center"
        android:onClick="onClick"
        android:text="Search"
        android:layout_marginTop="18dp"
        android:layout_below="@+id/editText"
        android:layout_centerHorizontal="true" />

    <ListView
        android:id="@+id/listView"
        android:layout_width="wrap_content"
        android:layout_height="333dp"

        android:layout_marginTop="34dp"
        android:layout_below="@+id/button"
        android:layout_alignParentStart="true" />


</RelativeLayout>`

JSON data Its for Bangalore as an example. For eg

{  
   "postalCodes":[  
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.59443998336792,
         "countryCode":"IN",
         "postalCode":"560001",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Bangalore G.P.O.",
         "lat":12.991448503615459
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.59443998336792,
         "countryCode":"IN",
         "postalCode":"560001",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Bangalore Bazaar",
         "lat":12.991448503615459
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.59443998336792,
         "countryCode":"IN",
         "postalCode":"560001",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Rajbhavan (Bangalore)",
         "lat":12.991448503615459
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore South",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.59368896484375,
         "countryCode":"IN",
         "postalCode":"560002",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Bangalore Corporation Building",
         "lat":12.97194016928975
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.12604139137574,
         "countryCode":"IN",
         "postalCode":"560009",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Bangalore Dist Offices Bldg",
         "lat":13.0642536587272
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.54905700683594,
         "countryCode":"IN",
         "postalCode":"560010",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Industrial Estate (Bangalore)",
         "lat":12.984736805762962
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore South",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.5673389434814,
         "countryCode":"IN",
         "postalCode":"560018",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Chamrajpet (Bangalore)",
         "lat":12.9603975402696
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.54813032113138,
         "countryCode":"IN",
         "postalCode":"560024",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Anandnagar (Bangalore)",
         "lat":12.971373314490803
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.640380859375,
         "countryCode":"IN",
         "postalCode":"560038",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Indiranagar (Bangalore)",
         "lat":12.974282086640057
      },
      {  
         "adminCode2":"572",
         "adminName3":"Bangalore North",
         "adminCode1":"19",
         "adminName2":"Bangalore",
         "lng":77.32035308234025,
         "countryCode":"IN",
         "postalCode":"560040",
         "adminName1":"Karnataka",
         "ISO3166-2":"KA",
         "placeName":"Vijayanagar (Bangalore)",
         "lat":13.00637724835858
      }
   ]
}

It should display this JSON data in the ListView. The program is running fine without any errors. The JSON data is displayed in the logcat but not the ListView. I searched all the stackoverflow solution but nothing worked for me.

Answer 1

Your logic is wrong, you are checking if your data is empty. Change your code like this:

if(!searchResult.isEmpty()){

                        ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this,android.R.layout.simple_list_item_1,searchResult);
                        lv.setAdapter(adapter);
                        adapter.notifyDataSetChanged();
                    }

Use the "!" to change the boolean value