因此，我尝试从 Json 文件在地图上显示标记，但它们没有出现，我已将其范围缩小到该行
map = mapFragment.getMapAsync(this);
它给了我错误
不兼容的类型：
必需：com.google.android.gms.maps.GoogleMap 找到：无效
这是其余的代码：
public class MainActivity extends FragmentActivity implements OnMapReadyCallback {
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);
map = mapFragment.getMapAsync(this);
if (map != null) {
//setUpMap();
new MarkerTask().execute();
}
}
}
@Override
public void onMapReady(GoogleMap googleMap) {
map = googleMap;
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)
))
);
}
}
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);
}
}
}
}
