最近想做一个程序，需要用到获取手机的地理位置，网上一搜一摞一摞的，但基本方法还是一样的。于是，找了一个比较工整的，看了下程序的逻辑，便直接用了。但是发现location每次都获取为null, 最后改完之后代码如下：
1.AndroidManifest.xml 文件中加入以下许可：
1 <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"></uses-permission> 2 <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"></uses-permission>
2.程序界面 main.xml 文件代码：
1 <?xml version="1.0" encoding="utf-8"?> 2 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 3 android:orientation="vertical" 4 android:layout_width="fill_parent" 5 android:layout_height="fill_parent" 6 > 7 <Button android:id="@+id/query" 8 android:text="查询所在城市" 9 android:layout_width="fill_parent" android:layout_height="wrap_content"/> 10 <TextView android:id="@+id/cityString" 11 android:layout_width="fill_parent" android:layout_height="wrap_content" 12 /> 13 </LinearLayout>
3. MainActivity.java 代码：
1 public class MainActivity extends Activity { 2 3 Button queryButton; 4 TextView cityString; 5 6 7 /** Called when the activity is first created. */ 8 @Override 9 public void onCreate(Bundle savedInstanceState) { 10 super.onCreate(savedInstanceState); 11 setContentView(R.layout.main); 12 13 queryButton = (Button)findViewById(R.id.query); 14 cityString = (TextView)findViewById(R.id.cityString); 15 16 queryButton.setOnClickListener(new OnClickListener() { 17 18 @Override 19 public void onClick(View v) { 20 LocationManager locationManager; 21 String serviceName = Context.LOCATION_SERVICE; 22 locationManager = (LocationManager) getSystemService(serviceName); 23 // String provider = LocationManager.GPS_PROVIDER; 24 Criteria criteria = new Criteria(); 25 criteria.setAccuracy(Criteria.ACCURACY_FINE); 26 criteria.setAltitudeRequired(false); 27 criteria.setBearingRequired(false); 28 criteria.setCostAllowed(true); 29 criteria.setPowerRequirement(Criteria.POWER_LOW); 30 String provider = locationManager.getBestProvider(criteria, true); 31 locationManager.requestLocationUpdates(provider, 2000, 10, 32 locationListener); 33 Location location = locationManager.getLastKnownLocation(provider); 34 while (location == null) { 35 location = locationManager.getLastKnownLocation(provider); 36 } 37 updateWithNewLocation(location); 38 locationManager.removeUpdates(locationListener); 39 } 40 }); 41 } 42 43 private final LocationListener locationListener = new LocationListener() { 44 public void onLocationChanged(Location location) { 45 updateWithNewLocation(location); 46 } 47 48 public void onProviderDisabled(String provider) { 49 updateWithNewLocation(null); 50 } 51 52 public void onProviderEnabled(String provider) { 53 } 54 55 public void onStatusChanged(String provider, int status, Bundle extras) { 56 } 57 }; 58 59 private void updateWithNewLocation(Location location) { 60 String latLongString; 61 TextView myLocationText; 62 myLocationText = (TextView) findViewById(R.id.cityString); 63 if (location != null) { 64 double lat = location.getLatitude(); 65 double lng = location.getLongitude(); 66 latLongString = "纬度:" + lat + "\n经度:" + lng + "\n"; 67 68 Geocoder gc = new Geocoder(MainActivity.this, Locale.getDefault()); 69 try { 70 // 取得地址相关的一些信息\经度、纬度 71 List<Address> addresses = gc.getFromLocation(lat, lng, 1); 72 StringBuilder sb = new StringBuilder(); 73 if (addresses.size() > 0) { 74 Address address = addresses.get(0); 75 sb.append(address.getLocality()).append("\n"); 76 latLongString = latLongString + sb.toString(); 77 } 78 } catch (IOException e) { 79 } 80 81 } else { 82 latLongString = "无法获取地理信息"; 83 } 84 myLocationText.setText("您当前的位置是:\n" + latLongString); 85 } 86 }
之前看的网上的代码，没有34~36行，结果获取出来location值为null，现在的代码通过手机位置移动事件给location赋值，再加上这三行之后就可以了。后来看见《Android开发入门教程》里有一句话：
“getLastKnownPosition() 返回近期所处的位置，但“近期”也许已经过期（例如，电话关掉）或者甚至是 null （如果没有为程序提供位置记录）”。
所以，后来想也许调用两次这个函数就可以，不必使用while循环。不过没有测试，如果哪位高人觉得程序有问题请多指教。