谷歌地图 api 没有在正确的位置放置标记

Question

我的代码应该在进入应用程序时找出用户的位置并在地图上放置一个标记。我的位置值始终等于 null，并且永远不会收到值。

if (location != null) {
                lat = (int) (location.getLatitude() * 1E6);
                longi = (int) (location.getLongitude() * 1E6);
                GeoPoint ourLocation = new GeoPoint(lat, longi);
                OverlayItem overlayItem = new OverlayItem(ourLocation, "AYO",
                        "Whats good yo");
                CustomPinpoint custom = new CustomPinpoint(d, CampusMap.this);
                custom.insertPinpoint(overlayItem);
                overlayList.add(custom);

            } else {
                Toast.makeText(CampusMap.this, "Couldn't get provider",
                        Toast.LENGTH_SHORT).show();

            }

        }

Answer 1

我在制作 GPS RPG 时遇到了一个相对类似的问题，以下是我注意到的一些事情：

首先，最初找到您的位置可能需要一段时间，这会导致该问题，因为您只检查位置是否为空。

您可能还需要确保在执行任何操作之前实际启用了设备的定位服务：

private boolean doLocationsCheck(){
    if(!checkLocationEnabled()){

        final CharSequence[] items = {"Yes", "No"};

        AlertDialog.Builder builder = new AlertDialog.Builder(mContext);
        builder.setCancelable(false);
        builder.setTitle("Location must be enabled to play this game! Would you like to enable it now?");
        builder.setItems(items, new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int item) {
                final int i = item;
                runOnUiThread(new Runnable() {
                    public void run() {                         
                        if(i == 0){
                            Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                            startActivity(intent);
                            quit();
                        }
                        else{
                            quit();
                        }

                    }
                });
            }


        }).show();
        AlertDialog alert = builder.create();

        return false;

    }
    else {
        return true;
    }
}

private boolean checkLocationEnabled(){

    LocationManager service = (LocationManager) getSystemService(LOCATION_SERVICE);
    boolean enabled = service.isProviderEnabled(LocationManager.GPS_PROVIDER) || service.isProviderEnabled(LocationManager.NETWORK_PROVIDER);

    return enabled;
}

在确定提供程序可用后，我设置如下连接：

    private void setupLocation() {

    LocationManager locationManager = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);

    LocationListener locationListener = new LocationListener() {
        public void onLocationChanged(final Location location) {
            runOnUiThread(new Runnable() {
                public void run() {
                    mLocation = location;
                    //Log.d(TAG, "Latitude: " + location.getLatitude() + " - Longitude: " + location.getLongitude());

                    saveLocation();
                }
            });   
        }

        public void onStatusChanged(String provider, int status, Bundle extras) {}

        public void onProviderEnabled(String provider) {}

        public void onProviderDisabled(String provider) {}
    };

            //Can set to GPS or network, whichever is available
    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListener);
}

该位置在更新时设置在全局变量中，然后保存到首选项中。这样，如果启用了提供程序，但需要一段时间来检索位置，用户仍然可以继续使用应用程序存储的最后一个已知位置（不适用于程序第一次正在运行）。

我知道我在那里遗漏了很多，但我认为这并不是真正必要的，因为它要么是不言自明的，要么已经在之前的答案中解释过。

干杯~

Answer 2

你必须在onstartActivity中在oncreate之前初始化locationlistener，以便它在onCreate之前获取location值。

Answer 3

 /*
 * getting the best location using the location manager
 * Constants.MINIMUM_TIME_BETWEEN_UPDATES = 1000 Constants.MINIMUM_TIME_BETWEEN_UPDATES     = 1
 */
LocationManager mLocation;
private String mBestProvider;
 //   in your onCreate() do the following
    mLocation = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    Criteria criteria = new Criteria();
mBestProvider = mLocation.getBestProvider(criteria, false);
Location location = mLocation.getLastKnownLocation(mBestProvider);
mLocation.requestLocationUpdates(
            LocationManager.GPS_PROVIDER, 
            Constants.MINIMUM_TIME_BETWEEN_UPDATES, 
            Constants.MINIMUM_DISTANCE_CHANGE_FOR_UPDATES,
            new LocationListenerManager()
    );


// and use the following locationListener inner class


private class LocationListenerManager implements LocationListener {

    public void onLocationChanged(Location location) {
        String message = String.format(
                "New Location \n Longitude: %1$s \n Latitude: %2$s",
                location.getLongitude(), location.getLatitude()
        );
        latitude = location.getLatitude();
        longitude = location.getLongitude();
        Toast.makeText(MapViewActivity.this, message, Toast.LENGTH_LONG).show();
        Log.v("poiint=====", ""+message);

    }

    public void onStatusChanged(String s, int i, Bundle b) {
        Toast.makeText(MapViewActivity.this, "Provider status changed",
                Toast.LENGTH_LONG).show();
    }

    public void onProviderDisabled(String s) {
        Toast.makeText(MapViewActivity.this,
                "Provider disabled by the user. GPS turned off",
                Toast.LENGTH_LONG).show();
    }

    public void onProviderEnabled(String s) {
        Toast.makeText(MapViewActivity.this,
                "Provider enabled by the user. GPS turned on",
                Toast.LENGTH_LONG).show();
    }

}