只需从 JSON 接收一个数据对象

Posted 2023-04-19

【中文标题】只需从 JSON 接收一个数据对象

【英文标题】：Just recieve one Dataobject from JSON

【发布时间】：2017-08-26 19:07:41

【问题描述】：

我尝试将地图标记从 JSON 获取到 MapActivity。 我只是从 JSON 中得到第一个，其他的没有显示在我的地图中。 我该如何解决我的问题。 这是我的地图活动：

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback 
private ProgressDialog pDialog;
private GoogleMap mMap;
private static String url="http://partypeople.bplaced.net/markers.json";
ArrayList<HashMap<String, String>> contactList;
private String TAG = MainActivity.class.getSimpleName();
double latitude;
double longitude;
String namec;

@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Override
protected void onCreate(Bundle savedInstanceState) 

    this.requestWindowFeature(Window.FEATURE_NO_TITLE);


    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test);
    contactList = new ArrayList<>();
    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map3);
    mapFragment.getMapAsync(this);




private class GetContacts extends AsyncTask<Void, Void, Void> 

    @Override
    protected void onPreExecute() 
        super.onPreExecute();


    

    @Override
    protected Void doInBackground(Void... arg0) 
        HttpHandler sh = new HttpHandler();


        String jsonStr = sh.makeServiceCall(url);

        Log.e(TAG, "Response from url: " + jsonStr);

        if (jsonStr != null) 
            try 
                JSONObject jsonObj = new JSONObject(jsonStr);


                JSONArray contacts = jsonObj.getJSONArray("markers");


                for (int i = 0; i < contacts.length(); i++) 
                    JSONObject c = contacts.getJSONObject(i);

                    String id = c.getString("id");
                    String name = c.getString("name");
                    String address = c.getString("address");
                    String lat = c.getString("lat");
                    String lng = c.getString("lng");




                    // tmp hash map for single contact
                    HashMap<String, String> contact = new HashMap<>();

                    // adding each child node to HashMap key => value
                    contact.put("id", id);
                    contact.put("name", name);
                    contact.put("address",address);
                    contact.put("lat", lat);
                    contact.put("lng", lng);

                    latitude = Double.parseDouble(lat); longitude = Double.parseDouble(lng);
                    contactList.add(contact);
                    namec = name;


                
             catch (final JSONException e) 
                Log.e(TAG, "Json parsing error: " + e.getMessage());
                runOnUiThread(new Runnable() 
                    @Override
                    public void run() 
                        Toast.makeText(getApplicationContext(),
                                "Json parsing error: " + e.getMessage(),
                                Toast.LENGTH_LONG)
                                .show();
                    
                );

            
         else 
            Log.e(TAG, "Couldn't get json from server.");
            runOnUiThread(new Runnable() 
                @Override
                public void run() 
                    Toast.makeText(getApplicationContext(),
                            "Couldn't get json from server. Check LogCat for possible errors!",
                            Toast.LENGTH_LONG)
                            .show();
                
            );

        

        return null;
    

    @Override
    protected void onPostExecute(Void result) 
        super.onPostExecute(result);

            LatLng P1 = new LatLng(latitude, longitude);

            mMap.addMarker(new MarkerOptions().position(P1).title(namec));
            mMap.moveCamera(CameraUpdateFactory.newLatLng(P1));

    


@Override
public void onMapReady(GoogleMap googleMap) 

    mMap = googleMap;
    new GetContacts().execute();
    mMap.setMyLocationEnabled(true);

这是我的 JSON：

"markers": [

    
            "id": "c201",
            "name": "Munic",
            "address": "try",
            "lat": "48.142281",
            "lng" : "11.550613"


    ,
   
            "id": "c205",
            "name": "Berlin",
            "address": "test",
            "lat": "43.142281",
            "lng" : "11.550613"


    

]

这是我的 httpHandler：

公共类 HttpHandler

private static final String TAG = HttpHandler.class.getSimpleName();

public HttpHandler() 


public String makeServiceCall(String reqUrl) 
    String response = null;
    try 
        URL url = new URL(reqUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        // read the response
        InputStream in = new BufferedInputStream(conn.getInputStream());
        response = convertStreamToString(in);
     catch (MalformedURLException e) 
        Log.e(TAG, "MalformedURLException: " + e.getMessage());
     catch (ProtocolException e) 
        Log.e(TAG, "ProtocolException: " + e.getMessage());
     catch (IOException e) 
        Log.e(TAG, "IOException: " + e.getMessage());
     catch (Exception e) 
        Log.e(TAG, "Exception: " + e.getMessage());
    
    return response;


private String convertStreamToString(InputStream is) 
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    StringBuilder sb = new StringBuilder();

    String line;
    try 
        while ((line = reader.readLine()) != null) 
            sb.append(line).append('\n');
        
     catch (IOException e) 
        e.printStackTrace();
     finally 
        try 
            is.close();
         catch (IOException e) 
            e.printStackTrace();
        
    
    return sb.toString();

【参考方案1】：

您的问题出在 onPostExecute 中，您只在地图上添加了一个标记。 你应该在那里使用你的联系人列表：

for (HashMap<String, String> contact: contactList) 
    LatLng P1 = new LatLng(
                    Double.parseDouble(contact.get("lat")),
                    Double.parseDouble(contact.get("lng")));

    mMap.addMarker(new MarkerOptions().position(P1).title(contact.get("name")));
    mMap.moveCamera(CameraUpdateFactory.newLatLng(P1));

【讨论】：

我试过了，但它没有运行，只显示了一个标记

对不起，现在它工作正常我有一个错误:)