我当前的位置总是返回 null.我怎样才能解决这个问题? [英] My current location always returns null. How can I fix this?

问题描述

我正在尝试为一个 android 项目查找我当前的位置.加载应用程序时，我的当前位置始终为空.我已经在清单等中设置了权限.当我找到当前位置时，我打算使用坐标来查找到地图上其他位置的距离.我的代码片段如下.为什么我总是得到一个空值?

I am trying to find my current location for an android project. When the application is loaded my current location is always null. I have set up the permissions in the manifest etc. When I find the current location I intend to use the coordinates to find distances to other locations on the map. My code snippet is below. Why do I always get a null value?

locMan = (LocationManager) getSystemService(Context.LOCATION_SERVICE);          
Criteria crit = new Criteria();     
towers = locMan.getBestProvider(crit, false);
location = locMan.getLastKnownLocation(towers);    

if (location != null) {                 
    System.out.println("Location is not null!");
    lat = (int) (location.getLatitude() *1E6);
    longi = (int) (location.getLongitude() * 1E6);
    GeoPoint ourLocation = new GeoPoint(lati, longi);
    OverlayItem overlayItem = new OverlayItem(ourLocation, "1st String",
                                                            "2nd String");
    CustomPinpoint custom = new CustomPinpoint(d, MainMap.this);
    custom.insertPinpoint(overlayItem);
    overlayList.add(custom);
    overlayList.clear();
} else {
   System.out.println("Location is null! " + towers);
   Toast.makeText(MainMap.this, "Couldn't get provider",Toast.LENGTH_SHORT)
                                                                    .show();
}

推荐答案

getLastKnownLocation() 使用其他应用程序先前找到的位置.如果没有应用程序这样做，则 getLastKnownLocation() 将返回 null.

getLastKnownLocation() uses the location(s) previously found by other applications. if no application has done this, then getLastKnownLocation() will return null.

您可以对代码做一件事，以更好地获得最后一个已知位置 - 迭代所有启用的提供者，而不仅仅是最好的提供者.例如，

One thing you can do to your code to have a better chance at getting as last known location- iterate over all of the enabled providers, not just the best provider. For example,

private Location getLastKnownLocation() {
    List<String> providers = mLocationManager.getProviders(true);
    Location bestLocation = null;
    for (String provider : providers) {
        Location l = mLocationManager.getLastKnownLocation(provider);
        ALog.d("last known location, provider: %s, location: %s", provider,
                l);

        if (l == null) {
            continue;
        }
        if (bestLocation == null
                || l.getAccuracy() < bestLocation.getAccuracy()) {
            ALog.d("found best last known location: %s", l);
            bestLocation = l;
        }
    }
    if (bestLocation == null) {
        return null;
    }
    return bestLocation;
}

如果您的应用在没有位置的情况下无法处理，并且如果没有最后的已知位置，您将需要监听位置更新.你可以看看这个类的例子，

If your app can't deal without having a location, and if there's no last known location, you will need to listen for location updates. You can take a look at this class for an example,

https://github.com/farble1670/autobright/blob/master/src/org/jtb/autobright/EventService.java

参见方法 onStartCommand()，它检查网络提供程序是否已启用.如果不是，则使用最后一个已知位置.如果启用，它会注册以接收位置更新.

See the method onStartCommand(), where it checks if the network provider is enabled. If not, it uses last known location. If it is enabled, it registers to receive location updates.

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