Question

我有位置marker的arraylist。我有这种方法来排序列表。然后我将列表中的第一个lat和long分配给一个变量，这样我就可以得到最近的商店。

                Collections.sort(marker, new Comparator<Markers>() {
                    @Override
                    public int compare(Markers a, Markers b) {
                        Location locationA = new Location("point A");
                        locationA.setLatitude(a.latitude);
                        locationA.setLongitude(a.longitude);
                        Location locationB = new Location("point B");
                        locationB.setLatitude(b.latitude);
                        locationB.setLongitude(b.longitude);
                        float distanceOne = currPos.distanceTo(locationA);
                        float distanceTwo = currPos.distanceTo(locationB);
                        return Float.compare(distanceOne, distanceTwo);
                    }
                });
                nearest = new LatLng(marker.get(0).latitude, marker.get(0).longitude);

但是，当我使用nearest变量在其上放置标记时，地图上没有贴出任何标记。当我检查nearest的值时，它不包含任何坐标。我错过了什么吗？这是我的整个MapsActivity.java：

public class MapsActivity extends FragmentActivity implements OnMapReadyCallback,
    GoogleApiClient.ConnectionCallbacks,
    GoogleApiClient.OnConnectionFailedListener,
    LocationListener {

private GoogleMap mMap;
GoogleApiClient mGoogleApiClient;
Location mLastLocation;
Marker mCurrLocationMarker;
LocationRequest mLocationRequest;
private static LatLng nearest;
private static Location currPos;

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

    if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        checkLocationPermission();
    }

    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
            .findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);

    fetchData();
}


@Override
public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
    mMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);

    if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION)
                == PackageManager.PERMISSION_GRANTED) {
            buildGoogleApiClient();
            mMap.setMyLocationEnabled(true);
            mMap.addMarker(new MarkerOptions()
                    .position(new LatLng(nearest.latitude,nearest.longitude))
                    .title("Nearest Store"));
        }
    }
    else {
        buildGoogleApiClient();
        mMap.setMyLocationEnabled(true);
    }
}

public void fetchData() {
    new AsyncTask() {
        private List<Markers> marker;
        private JSONArray jsonArray;
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            marker = new ArrayList();
        }

        @Override
        protected Object doInBackground(Object[] objects) {
            return null;
        }

        @Override
        protected void onPostExecute(Object o) {
            super.onPostExecute(o);
            try {
                Intent mapsIntent = getIntent();
                String jSonArray = mapsIntent.getStringExtra("jsonArray");
                jsonArray = new JSONArray(jSonArray);

                for(int i = 0; i < jsonArray.length(); i++) {
                    Markers branch = new Markers();
                    branch.latitude = Float.parseFloat(jsonArray.getJSONObject(i).getString("latitude"));
                    branch.longitude = Float.parseFloat(jsonArray.getJSONObject(i).getString("longitude"));

                    marker.add(branch);
                }


                Collections.sort(marker, new Comparator<Markers>() {
                    @Override
                    public int compare(Markers a, Markers b) {
                        Location locationA = new Location("point A");
                        locationA.setLatitude(a.latitude);
                        locationA.setLongitude(a.longitude);
                        Location locationB = new Location("point B");
                        locationB.setLatitude(b.latitude);
                        locationB.setLongitude(b.longitude);
                        float distanceOne = currPos.distanceTo(locationA);
                        float distanceTwo = currPos.distanceTo(locationB);
                        return Float.compare(distanceOne, distanceTwo);
                    }
                });
                nearest = new LatLng(marker.get(0).latitude, marker.get(0).longitude);
            } catch (Exception ex) {
                Log.d("Error", ex.toString());
            }
        }
    }.execute();
}

private class Markers {
    public float latitude;
    public float longitude;
}

protected synchronized void buildGoogleApiClient() {
    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .addConnectionCallbacks(this)
            .addOnConnectionFailedListener(this)
            .addApi(LocationServices.API)
            .build();
    mGoogleApiClient.connect();
}

@Override
public void onConnected(Bundle bundle) {

    mLocationRequest = new LocationRequest();
    mLocationRequest.setInterval(1000);
    mLocationRequest.setFastestInterval(1000);
    mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY);
    if (ContextCompat.checkSelfPermission(this,
            Manifest.permission.ACCESS_FINE_LOCATION)
            == PackageManager.PERMISSION_GRANTED) {
        LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this);
    }

}

@Override
public void onConnectionSuspended(int i) {

}

@Override
public void onLocationChanged(Location location) {

    mLastLocation = location;
    if (mCurrLocationMarker != null) {
        mCurrLocationMarker.remove();
    }

    //Place current location marker
    LatLng latLng = new LatLng(location.getLatitude(), location.getLongitude());
    currPos = location;
    MarkerOptions markerOptions = new MarkerOptions();
    markerOptions.position(latLng);
    markerOptions.title("Current Location");
    markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA));
    mCurrLocationMarker = mMap.addMarker(markerOptions);

    mMap.moveCamera(CameraUpdateFactory.newLatLng(latLng));
    mMap.animateCamera(CameraUpdateFactory.zoomTo(11));

    if (mGoogleApiClient != null) {
        LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient, this);
    }

}

@Override
public void onConnectionFailed(ConnectionResult connectionResult) {

}

public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99;
public boolean checkLocationPermission(){
    if (ContextCompat.checkSelfPermission(this,
            Manifest.permission.ACCESS_FINE_LOCATION)
            != PackageManager.PERMISSION_GRANTED) {

        if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                Manifest.permission.ACCESS_FINE_LOCATION)) {

            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                    MY_PERMISSIONS_REQUEST_LOCATION);


        } else {

            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                    MY_PERMISSIONS_REQUEST_LOCATION);
        }
        return false;
    } else {
        return true;
    }
}

@Override
public void onRequestPermissionsResult(int requestCode,
                                       String permissions[], int[] grantResults) {
    switch (requestCode) {
        case MY_PERMISSIONS_REQUEST_LOCATION: {
            if (grantResults.length > 0
                    && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                if (ContextCompat.checkSelfPermission(this,
                        Manifest.permission.ACCESS_FINE_LOCATION)
                        == PackageManager.PERMISSION_GRANTED) {

                    if (mGoogleApiClient == null) {
                        buildGoogleApiClient();
                    }
                    mMap.setMyLocationEnabled(true);
                }

            } else {

                Toast.makeText(this, "Permission Denied", Toast.LENGTH_LONG).show();
            }
            return;
        }

    }
}

}

Answer 1

你的两个线程之间存在竞争条件。

mapFragment.getMapAsync(this);  // thread 1

fetchData();  // thread 2

线程1需要线程2完成并指定nearest才能工作。否则为空

您可以在onPostExecute结束时调用mapFragment.getMapAsync(MapsActivity.this);，但是......

您的Asynctask目前毫无意义，因为后台任务不会获取任何数据。

最近的位置返回null

1 个答案: