java - 如何从 Android map Activity 中的 url 获取 JSON 数据

Question

嗨，我想知道如何从 URL 获取 JSON 数据并将其放入 android studio 中的 map Activity 中，这将替换默认位置 syndey？我不知道如何做到这一点，因为大多数在线教程没有意义。

这是我想通过 URL 检索的数据

{"Users":[{"name":"Diaz","lon":"51.1251635","lat":"51.296910"},{"name":"Chris","lon":"51.139409","lat":"51.295825"}}

这是 map Activity 生成的默认代码

import android.os.Bundle;
import android.renderscript.ScriptGroup;
import android.support.v4.app.FragmentActivity;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback {

    private GoogleMap mMap;
    private GoogleMap nMap;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_maps);
        SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
                .findFragmentById(R.id.map);
        mapFragment.getMapAsync(this);

    }


    /**
     * Manipulates the map once available.
     * This callback is triggered when the map is ready to be used.
     * This is where we can add markers or lines, add listeners or move the camera. In this case,
     * we just add a marker near Sydney, Australia.
     * If Google Play services is not installed on the device, the user will be prompted to install
     * it inside the SupportMapFragment. This method will only be triggered once the user has
     * installed Google Play services and returned to the app.
     */
    @Override
    public void onMapReady(GoogleMap googleMap) {
        mMap = googleMap;

        // Add a marker in Sydney, Australia, and move the camera.
        LatLng sydney = new LatLng(512.33,11.2333);
        mMap.addMarker(new MarkerOptions().position(sydney).title("Marker in Sydney"));
        mMap.moveCamera(CameraUpdateFactory.newLatLng(sydeny));
        mMap.getMaxZoomLevel();
    }


}

Answer 1

首先，在 map 上显示您当前的位置。您所需要做的就是使用谷歌地图获取您首选位置的坐标。您现在可以使用此值创建 LatLng 对象。您的应用程序当前显示悉尼，因为这是 map 相机所在的位置。您在同一 LatLng 处也有一个标记。

您可以简单地获取要显示的位置的坐标并将其传递到 Map 对象中。

回到您的主要问题，即从 URL 获取 JSON 数据；我可以说这很容易实现，并且根据您所询问的上下文，我可以推断您可能正在尝试查询谷歌地图 API。

像 Retrofit( http://square.github.io/retrofit/ ) 这样的库可以帮助您轻松完成此任务。只是不要忘记从后台线程执行该操作。

使用基本的 HttpURLConnection

public JSONObject queryGoogleDistanceApi(String origin, String destination, String API_KEY_PLACES) throws Exception{
    String Url = "https://maps.googleapis.com/maps/api/distancematrix/json?origins=" + origin + "&destinations=" + destination + "&mode=driving&language=en&key=" + API_KEY_PLACES;

    HttpURLConnection conn = null;
    StringBuilder jsonResults = new StringBuilder();
    URL url = new URL(Url);
    Log.d(TAG, Url);
    conn = (HttpURLConnection) url.openConnection();
    InputStreamReader in = new InputStreamReader(conn.getInputStream());
    // Load the results into a StringBuilder
    int read;
    char[] buff = new char[1024];
    while ((read = in.read(buff)) != -1) {
        jsonResults.append(buff, 0, read);
    }
    if (conn != null) {
        conn.disconnect();
    }

    JSONObject object = new JSONObject(jsonResults.toString());
    return object;
}