我正在尝试从android中的gps检索我的lat和lng的另一个全新尝试。使用新代码，它首先成功打开了我的活动，但我没有获得任何gps坐标。然后，我拔掉了手机的电话，将它移向窗户，最终崩溃了。然后我决定再试一次，但实际插入它，以便在窗口崩溃时获取错误报告。
我第二次启动应用程序时，我现在无法再进入活动而不会因为此错误而崩溃：
12-10 11:53:52.923 398-398/com.beerportfolio.beerportfoliopro E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.beerportfolio.beerportfoliopro/com.example.beerportfoliopro.FindBrewery}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2517)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2574)
at android.app.ActivityThread.access$600(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1413)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:5789)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:843)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.beerportfoliopro.FindBrewery.onLocationChanged(FindBrewery.java:67)
at com.example.beerportfoliopro.FindBrewery.onCreate(FindBrewery.java:42)
at android.app.Activity.performCreate(Activity.java:5195)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1111)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2473)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2574)
at android.app.ActivityThread.access$600(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1413)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:5789)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:843)
at dalvik.system.NativeStart.main(Native Method)
12-10 11:53:52.933 24060-24091/system_process E/EmbeddedLogger﹕ App crashed! Process: com.beerportfolio.beerportfoliopro
12-10 11:53:52.933 24060-24091/system_process E/EmbeddedLogger﹕ App crashed! Package: com.beerportfolio.beerportfoliopro v22 (3.0)
12-10 11:53:52.933 24060-24091/system_process E/EmbeddedLogger﹕ Application Label: BeerPortfolio Pro
我的活动代码是：
public class FindBrewery extends Activity implements LocationListener {
private TextView latituteField;
private TextView longitudeField;
private LocationManager locationManager;
private String provider;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.beer_location_list);
//latituteField = (TextView) findViewById(R.id.TextView02);
//longitudeField = (TextView) findViewById(R.id.TextView04);
// Get the location manager
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
// Define the criteria how to select the locatioin provider -> use
// default
Criteria criteria = new Criteria();
provider = locationManager.getBestProvider(criteria, false);
Location location = locationManager.getLastKnownLocation(provider);
// Initialize the location fields
if (location != null) {
System.out.println("Provider " + provider + " has been selected.");
onLocationChanged(location);
} else {
Toast.makeText(this, "Location Not available " + provider,
Toast.LENGTH_SHORT).show();
}
}
/* Request updates at startup */
@Override
protected void onResume() {
super.onResume();
locationManager.requestLocationUpdates(provider, 400, 1, this);
}
/* Remove the locationlistener updates when Activity is paused */
@Override
protected void onPause() {
super.onPause();
locationManager.removeUpdates(this);
}
@Override
public void onLocationChanged(Location location) {
int lat = (int) (location.getLatitude());
int lng = (int) (location.getLongitude());
latituteField.setText(String.valueOf(lat));
longitudeField.setText(String.valueOf(lng));
Toast.makeText(this, "Attempting async task" + provider,
Toast.LENGTH_SHORT).show();
//call asycn task for location
String url = "myURL";
Log.d("urlTest", url);
//async task goes here
new GetNearbyBreweries(this).execute(url);
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
@Override
public void onProviderEnabled(String provider) {
Toast.makeText(this, "Enabled new provider " + provider,
Toast.LENGTH_SHORT).show();
}
@Override
public void onProviderDisabled(String provider) {
Toast.makeText(this, "Disabled provider " + provider,
Toast.LENGTH_SHORT).show();
}
}
我想要完成的是，当活动开始时它会检索用户位置，然后将lng和lat发送到我的异步任务，然后从我的数据库中检索位置列表并填充列表。
答案 0 :(得分：3)
你的问题在这里：
Location location = locationManager.getLastKnownLocation(provider);
// Initialize the location fields
if (location != null) {
System.out.println("Provider " + provider + " has been selected.");
onLocationChanged(location);
您以编程方式呼叫onLocationChanged。这是错的。你真正想要的是locationManager.requestLocationUpdates。见这里：
您的位置为空，因为您告诉您的应用您有位置，而实际上您没有。这样做会导致NullPointerException：
int lat = (int) (location.getLatitude());
int lng = (int) (location.getLongitude());
latituteField.setText(String.valueOf(lat));
longitudeField.setText(String.valueOf(lng));
如果您等待触发位置更新，那么它将正常工作。
答案 1 :(得分：0)
或者你可能没有添加获取gps位置所需的权限，它可能会给你NullPointerException，因为它是空的。