Android获取经纬度失败求助：点击按钮无法定位

咱们一步步来分析你遇到的问题——点击按钮后始终弹出“Unable to Trace your location”，说明locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER)返回了null，下面是最可能的几个原因和对应的修复方案：

1. 仅依赖NETWORK_PROVIDER太局限 #

getLastKnownLocation只会返回该定位提供者缓存的最后一次有效位置，如果你的设备最近没通过网络定位过（比如刚开机、长时间没联网），或者当前网络信号不足以支撑定位，这个方法就会返回null。

建议你同时尝试GPS提供者，或者直接切换到更可靠的Fused Location Provider（Google推荐的现代定位API）。这里先给你修改一下现有代码，让它尝试多个定位源：

private void getLocation() {
    if (ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED 
        && ActivityCompat.checkSelfPermission(MainActivity.this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_LOCATION);
        return;
    }

    // 先尝试网络定位
    Location location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
    if (location == null) {
        // 网络定位失败，尝试GPS定位
        location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
    }

    if (location != null) {
        double latti = location.getLatitude();
        double longi = location.getLongitude();
        lattitude = String.valueOf(latti);
        longitude = String.valueOf(longi);
        textView.setText("Your current location is" + "\n" + "Lattitude = " + lattitude + "\n" + "Longitude = " + longitude);
    } else {
        Toast.makeText(this, "Unable to Trace your location", Toast.LENGTH_SHORT).show();
    }
}

2. 你可能没初始化LocationManager #

如果你的代码里没有初始化locationManager对象，调用getLastKnownLocation会直接报错（不过你这里是返回null，可能已经初始化了，但还是要确认）。确保在onCreate或者其他合适的地方添加初始化代码：

private LocationManager locationManager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // 初始化LocationManager
    locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
    // 其他初始化代码...
}

3. 设备的定位服务未开启 #

即使你申请了权限，如果用户设备的定位服务处于关闭状态，或者位置模式设置为“仅设备”但GPS没信号，定位提供者也无法返回位置。你可以添加逻辑检查定位服务是否开启，如果没开，引导用户去设置开启：

// 在获取位置前检查定位服务状态
private boolean isLocationEnabled() {
    return locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER) 
        || locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
}

// 在getLocation里调用
if (!isLocationEnabled()) {
    Toast.makeText(this, "Please enable location services", Toast.LENGTH_SHORT).show();
    // 跳转到定位设置界面
    Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
    startActivity(intent);
    return;
}

4. getLastKnownLocation本身不可靠 #

这个方法的设计就是返回缓存位置，不保证一定有值。如果需要实时获取当前位置，更好的方式是请求位置更新，或者使用Fused Location Provider的getCurrentLocation方法。比如用Fused的示例：

// 先添加依赖到build.gradle
// implementation 'com.google.android.gms:play-services-location:21.0.1'

private FusedLocationProviderClient fusedLocationClient;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    fusedLocationClient = LocationServices.getFusedLocationProviderClient(this);
}

private void getLocation() {
    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED 
        && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
        ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, REQUEST_LOCATION);
        return;
    }
    fusedLocationClient.getCurrentLocation(Priority.PRIORITY_HIGH_ACCURACY, null)
        .addOnSuccessListener(this, new OnSuccessListener<Location>() {
            @Override
            public void onSuccess(Location location) {
                if (location != null) {
                    double latti = location.getLatitude();
                    double longi = location.getLongitude();
                    lattitude = String.valueOf(latti);
                    longitude = String.valueOf(longi);
                    textView.setText("Your current location is" + "\n" + "Lattitude = " + lattitude + "\n" + "Longitude = " + longitude);
                } else {
                    Toast.makeText(MainActivity.this, "Unable to Trace your location", Toast.LENGTH_SHORT).show();
                }
            }
        });
}

按照上面的步骤排查，应该能解决你无法获取位置的问题。

内容的提问来源于stack exchange，提问作者Basil Shaikh