MAP getLastKnownLocation()返回null的解决

原文：http://blog.sina.com.cn/s/blog_74c22b210100sfix.html
这两天可憋坏我了，一直愁没什么题材可以充实我的博客，正巧最近遇到一个比较棘手的问题：

使用GPS定位无法获取当前的地理位置，即getLastKnownLocation方法始终返回null。

后来一篇博文<wbr><a href="http://blog.sina.com.cn/s/blog_74c22b210100s8hg.html" target="_blank">getLastKnownLocation()返回null的解决</a><wbr>帮了我大忙，在此对该博客作者表示感谢，但是有几点需要注意的，我觉得有必要补充一下，否则看了这篇博文也还是得不到当前的地理位置。</wbr></wbr>

第一：当使用GPS定位时，最好不要使用getLastKnownLocation方法获得当前位置对象Location，因为该对象可以在onLocationChanged的参数中由系统给予（根据文档，getLastKnownLocation有2方面功能：1. 获取当前地理位置2.如果当前位置定位不成功，则可以用此方法获取缓存中的上一次打开地图时定位的地理位置）。这样就避免了空指针异常。而且更重要的是GPS定位不是一下子就能定位成功的，在90%以上的情况下，getLastKnownLocation返回null

第二：LocationListener最好在Activity的onCreate（）方法中进行实例化

<wbr><wbr><wbr>实现系统的回调方法：</wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>onLocationChanged（finalLocation loc）</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>onProviderDisabled（final Strings）</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>onProviderEnabled（final Strings）</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>onStatusChanged（final String s,final int i, final Bundle b）</wbr></wbr></wbr></wbr></wbr>

第三：requestLocationUpdates必须要在onResume（）中进行注册监听. 且在onPause（）中进行反注 <wbr>册。</wbr>

第四：测试GPS是否定位成功，去一个空旷的地方去，不要有遮挡。这点非常重要，不然，你永远也不知道自己GPS定位是否成功。

以下是我用GPS成功获取当前地理位置的例子。希望能够帮助大家摆脱GPS定位的阴霾。

@Override

public void onCreate(final Bundle icicle) {

<wbr><wbr><wbr>super.onCreate(icicle);</wbr></wbr></wbr>

<wbr><wbr><wbr>this.setContentView(R.layout.activity_mapview);</wbr></wbr></wbr>

<wbr><wbr><wbr>mBtnDone =(Button) findViewById(R.id.btn_done);</wbr></wbr></wbr>

<wbr><wbr><wbr>mBtnDone.setOnClickListener(this);</wbr></wbr></wbr>

<wbr><wbr><wbr>mapView = (MapView) findViewById(R.id.map_view);</wbr></wbr></wbr>

<wbr><wbr><wbr>mapView.setBuiltInZoomControls(true);</wbr></wbr></wbr>

<wbr><wbr><wbr>mapController = mapView.getController();</wbr></wbr></wbr>

<wbr><wbr><wbr>mLocationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);</wbr></wbr></wbr>

<wbr><wbr><wbr>mDefaultMarker =getResources().getDrawable(R.drawable.map_redpin);</wbr></wbr></wbr>

<wbr><wbr><wbr>mDefaultMarker.setBounds(0, 0,mDefaultMarker.getIntrinsicWidth(),</wbr></wbr></wbr>

<wbr><wbr><wbr>mDefaultMarker.getIntrinsicHeight());</wbr></wbr></wbr>

<wbr><wbr><wbr>mBuoyOverlay = new BuoyItemizedOverlay(mDefaultMarker, this);</wbr></wbr></wbr>

<wbr><wbr><wbr>initDensityDpi();</wbr></wbr></wbr>

<wbr><wbr><wbr>mZoomLevel = mapView.getMaxZoomLevel() - 1;</wbr></wbr></wbr>

//<wbr>LocationListener最好在Activity的onCreate（）方法中进行实例化，当GPS获得Location时，会自<wbr><wbr><wbr><wbr>动调用onLocationChanged方法.</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr>mLocationListener = new LocationListener() {</wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr> @Override</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr> public voidonLocationChanged(final Location loc) {</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr> LogHelper.i(TAG,"onLocationChanged. loc: " + loc);</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr> if (loc != null) {</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>LogHelper.i(TAG, "onLocationChanged. latitude:"</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> + loc.getLatitude() + " ,longtitude: ".getLongitude());</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>GeoPoint geoPoint =MapUtils.getGeoPoint(loc);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mapController.animateTo(geoPoint);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>initBuoyOverlayItems(loc);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>} else {</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr>Toast(<wbr>MapViewActivity.this,<wbr>"Yourcurrent location is temporarily unavailable.",</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>Toast.LENGTH_SHORT).show();</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr>}</wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>// 当系统Setting -&gt; Location&amp; Security -&gt; Use wirelessnetworks取消勾选，Use GPS <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>satellites取消勾选时调用</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>public void onProviderDisabled(final String s){</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>LogHelper.i(TAG, "onProviderDisabled. ");</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr> // 当系统Setting -&gt; Location&amp; Security -&gt; Use wirelessnetworks勾选，Use GPS satellites勾 <wbr><wbr><wbr><wbr><wbr> 选时调用</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr> public void onProviderEnabled(final String s){</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr> LogHelper.i(TAG, "onProviderEnabled. ");</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr> }</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr> public void onStatusChanged(final String s,final int i, final Bundle b) {</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr> LogHelper.i(TAG, "onStatusChanged. ");</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr> }</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>};</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr>}</wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>@Override</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>public void onStart() {</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>super.onStart();</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>mapController.setZoom(mZoomLevel);</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr> if(!DoSomeGoodUtils.isNetworkAvailable(this)) {</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mBtnDone.setEnabled(false);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>showDialog(DIALOG_NO_NETWORK);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>} else{</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>// 判断UseGPS satellites.是否勾选</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>booleanisGpsEnabled = MapUtils.isGPSProviderAvaliable(this);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>// 判断Usewireless networks 是否勾选</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>booleanisWIFIEnabled = MapUtils.isWIFIProviderAvaliable(this);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>if(!isGpsEnabled &amp;&amp; !isWIFIEnabled){</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>如果都没有勾选，则弹出对话框，提示用户勾选。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> }</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> else {</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> Location lastKnownLocation =null;</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> // 如果只是Use GPSsatellites勾选，即指允许使用GPS定位</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>if(isGpsEnabled &amp;&amp; !isWIFIEnabled){<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>lastKnownLocation=mLocationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> mProviderName =LocationManager.GPS_PROVIDER;</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> // 如果只是Use wirelessnetworks勾选，即只允许使用网络定位。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>} else if(!isGpsEnabled&amp;&amp; isWIFIEnabled){</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>lastKnownLocation = <wbr><wbr>mLocationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mProviderName =LocationManager.NETWORK_PROVIDER;</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>//如果二者都勾选，优先使用GPS,因为GPS定位更精确。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr> } else if (isGpsEnabled&amp;&amp; isWIFIEnabled){<wbr><wbr><wbr><wbr><wbr><wbr><wbr>lastKnownLocation=mLocationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mProviderName =LocationManager.GPS_PROVIDER;</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>if (lastKnownLocation == null) {</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>lastKnownLocation=mLocationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mProviderName =LocationManager.NETWORK_PROVIDER;</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr> }</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr> if(!TextUtils.isEmpty(mProviderName)) {</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mLocationManager.requestLocationUpdates(</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mProviderName, 1000, 1,mLocationListener);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr> }</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr> //如果一下子就能定位成功，则执行以下代码，当用网络定位时，大都能一次性定位成功，当用GPS时，该代码不会起太大作用。</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>if (lastKnownLocation ！= null){</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mBtnDone.setEnabled(true);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr> // 获取当前地理位置</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr>GeoPoint lastKnownPoint =getLastKnownPoint(lastKnownLocation);</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr> // 以动画方式移动到该地理位置</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr> mapController.animateTo(lastKnownPoint);</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr> // 更新浮标。该方法在这里就不公开了。知道它的含义就行</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>initBuoyOverlayItems(lastKnownLocation);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr>

<wbr><wbr><wbr>}</wbr></wbr></wbr>

<wbr><wbr><wbr>}</wbr></wbr></wbr>

<wbr><wbr><wbr>@Override</wbr></wbr></wbr>

<wbr><wbr><wbr>protected void onResume() {</wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>super.onResume();</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>LogHelper.i(TAG, "onResume. Provider Name: " +mProviderName);</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr> if(!TextUtils.isEmpty(mProviderName)) {</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>//当GPS定位时，在这里注册requestLocationUpdates监听就非常重要而且必要。</wbr></wbr></wbr></wbr></wbr></wbr>

没有这句话，定位不能成功。

<wbr><wbr><wbr><wbr><wbr><wbr><wbr>mLocationManager.requestLocationUpdates(mProviderName,1000, 1,</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mLocationListener);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>@Override</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr>protected void onPause(){</wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>super.onPause();</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>//取消注册监听</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>if(mLocationManager != null) {</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mLocationManager.removeUpdates(mLocationListener);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr><wbr><wbr><wbr>}</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr>}</wbr></wbr></wbr>

}

对于定位方式：有些同行，更倾向于使用getBestProvider方法，但是我认为这种方式有他的弊端，不是所有的手机都支持<wbr> “使用getBestProvider获取最适合的Location”<wbr><span style="font-family:宋体">，最好就是使用网络定位和GPS定位</span>....</wbr></wbr>