android - 将 JSON 用于 Android map API : Markers not Showing up

Question

我正在尝试使用 JSON 为我的应用程序在我的 Google map 上创建标记，但由于某种原因，它们没有显示。 logcat 没有错误或警告，但没有显示标记。

我的 JSON 托管在这里:https://api.myjson.com/bins/4jb09

这是我的 Java:

package com.example.toshiba.jsonmap;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.util.Log;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * @author saxman
 */
public class MainActivity extends FragmentActivity {
    private static final String LOG_TAG = "ExampleApp";

    private static final String SERVICE_URL = "https://api.myjson.com/bins/4jb09";

    protected GoogleMap map;

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

    @Override
    protected void onResume() {
        super.onResume();
        setUpMapIfNeeded();
    }

    private void setUpMapIfNeeded() {
        if (map == null) {
            MapFragment mapFragment = (MapFragment) getFragmentManager()
                    .findFragmentById(R.id.map);
            mapFragment.getMap();
            if (map != null) {
                setUpMap();
            }
        }
    }

    private void setUpMap() {
        // Retrieve the city data from the web service
        // In a worker thread since it's a network operation.
        new Thread(new Runnable() {
            public void run() {
                try {
                    retrieveAndAddCities();
                } catch (IOException e) {
                    Log.e(LOG_TAG, "Cannot retrive cities", e);
                    return;
                }
            }
        }).start();
    }

    protected void retrieveAndAddCities() throws IOException {
        HttpURLConnection conn = null;
        final StringBuilder json = new StringBuilder();
        try {
            // Connect to the web service
            URL url = new URL(SERVICE_URL);
            conn = (HttpURLConnection) url.openConnection();
            InputStreamReader in = new InputStreamReader(conn.getInputStream());

            // Read the JSON data into the StringBuilder
            int read;
            char[] buff = new char[1024];
            while ((read = in.read(buff)) != -1) {
                json.append(buff, 0, read);
            }
        } catch (IOException e) {
            Log.e(LOG_TAG, "Error connecting to service", e);
            throw new IOException("Error connecting to service", e);
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }

        // Create markers for the city data.
        // Must run this on the UI thread since it's a UI operation.
        runOnUiThread(new Runnable() {
            public void run() {
                try {
                    createMarkersFromJson(json.toString());
                } catch (JSONException e) {
                    Log.e(LOG_TAG, "Error processing JSON", e);
                }
            }
        });
    }

    void createMarkersFromJson(String json) throws JSONException {
        // De-serialize the JSON string into an array of city objects
        JSONArray jsonArray = new JSONArray(json);
        for (int i = 0; i < jsonArray.length(); i++) {
            // Create a marker for each city in the JSON data.
            JSONObject jsonObj = jsonArray.getJSONObject(i);
            map.addMarker(new MarkerOptions()
                            .title(jsonObj.getString("name"))
                            .snippet(Integer.toString(jsonObj.getInt("population")))
                            .position(new LatLng(
                                    jsonObj.getJSONArray("latlng").getDouble(0),
                                    jsonObj.getJSONArray("latlng").getDouble(1)
                            ))
            );
        }
    }
}

Answer 1

我继续使用 AsyncTask 让您的代码正常工作。

下面是如何在 onCreate() 中调用它:

private void setUpMapIfNeeded() {
    if (map == null) {
        MapFragment mapFragment = (MapFragment) getFragmentManager()
                .findFragmentById(R.id.map);
        map = mapFragment.getMap();
        if (map != null) {
            //setUpMap();
            new MarkerTask().execute();
        }
    }
}

这是 AsyncTask，请注意，我继续将标记设为蓝色作为示例:

private class MarkerTask extends AsyncTask<Void, Void, String> {

        private static final String LOG_TAG = "ExampleApp";

        private static final String SERVICE_URL = "https://api.myjson.com/bins/4jb09";

        // Invoked by execute() method of this object
        @Override
        protected String doInBackground(Void... args) {

            HttpURLConnection conn = null;
            final StringBuilder json = new StringBuilder();
            try {
                // Connect to the web service
                URL url = new URL(SERVICE_URL);
                conn = (HttpURLConnection) url.openConnection();
                InputStreamReader in = new InputStreamReader(conn.getInputStream());

                // Read the JSON data into the StringBuilder
                int read;
                char[] buff = new char[1024];
                while ((read = in.read(buff)) != -1) {
                    json.append(buff, 0, read);
                }
            } catch (IOException e) {
                Log.e(LOG_TAG, "Error connecting to service", e);
                //throw new IOException("Error connecting to service", e); //uncaught
            } finally {
                if (conn != null) {
                    conn.disconnect();
                }
            }

            return json.toString();
        }

        // Executed after the complete execution of doInBackground() method
        @Override
        protected void onPostExecute(String json) {

            try {
                // De-serialize the JSON string into an array of city objects
                JSONArray jsonArray = new JSONArray(json);
                for (int i = 0; i < jsonArray.length(); i++) {
                    JSONObject jsonObj = jsonArray.getJSONObject(i);

                    LatLng latLng = new LatLng(jsonObj.getJSONArray("latlng").getDouble(0),
                            jsonObj.getJSONArray("latlng").getDouble(1));

                    //move CameraPosition on first result
                    if (i == 0) {
                        CameraPosition cameraPosition = new CameraPosition.Builder()
                                .target(latLng).zoom(13).build();

                        map.animateCamera(CameraUpdateFactory
                                .newCameraPosition(cameraPosition));
                    }

                    // Create a marker for each city in the JSON data.
                    map.addMarker(new MarkerOptions()
                            .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE))
                            .title(jsonObj.getString("name"))
                            .snippet(Integer.toString(jsonObj.getInt("population")))
                            .position(latLng));
                }
            } catch (JSONException e) {
                Log.e(LOG_TAG, "Error processing JSON", e);
            }

        }
    }

结果:

此外，如果您想要自定义信息窗口，您可以look at the documentation here .

我继续做了一个简单的例子，也适用于此。

设置InfoWindowAdapter的代码:

map.setInfoWindowAdapter(new GoogleMap.InfoWindowAdapter() {

            @Override
            public View getInfoWindow(Marker arg0) {
                return null;
            }

            @Override
            public View getInfoContents(Marker arg0) {

                View v = getLayoutInflater().inflate(R.layout.customlayout, null);

                TextView tLocation = (TextView) v.findViewById(R.id.location);

                TextView tSnippet = (TextView) v.findViewById(R.id.population);

                tLocation.setText(arg0.getTitle());

                tSnippet.setText(arg0.getSnippet());

                return v;

            }
        });

自定义布局.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="20dp"
    android:orientation="vertical"
    android:background="#000000">

    <TextView
        android:id="@+id/location"
        android:textColor="#D3649F"
        android:textStyle="bold"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <TextView
        android:id="@+id/population"
        android:textColor="#D3649F"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

结果: