我试图管理这样的事情：
如果GPS已关闭，请不要执行任何操作，如果已打开，请将相机放大到用户所在位置。然后，在位置按钮上，如果它被点击并且GPS关闭，则将其链接到设置活动（当然是Android）;然后如果再次点击它会放大。
否则，如果它已开启，则放大。
问题是，如果我打开应用程序并且GPS关闭，它会立即崩溃，但如果GPS打开则可以正常工作。
我需要更改/添加到我的代码才能使其正常工作？
MainActivity：
import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationManager;
import android.os.Bundle;
import android.view.Menu;
import android.widget.Toast;
import com.google.android.gms.location.LocationListener;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.GoogleMap.OnMyLocationButtonClickListener;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.model.LatLng;
public class MainActivity extends Activity implements LocationListener {
GoogleMap map;
public double longitude;
public double latitude;
Location location;
@SuppressWarnings("unused")
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
map = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
map.setMyLocationEnabled(true);
final Criteria criteria = new Criteria();
final LocationManager lm = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
lm.getBestProvider(criteria, true);
final Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
latitude = location.getLatitude();
longitude = location.getLongitude();
if (location != null) {
LatLng UserLoc = new LatLng(latitude, longitude);
map.animateCamera(CameraUpdateFactory.newLatLngZoom(UserLoc, 7));
} else {
Toast.makeText(getApplicationContext(), "cant get loc", Toast.LENGTH_LONG).show();
}
map.setOnMyLocationButtonClickListener(new OnMyLocationButtonClickListener() {
@Override
public boolean onMyLocationButtonClick() {
// if the Gps is off it openes a dialog to turn it off
if (!lm.isProviderEnabled(LocationManager.GPS_PROVIDER)) {
buildAlertMessageNoGps();
} else if (location == null) {
Toast.makeText(getApplicationContext(), "cant get loc", Toast.LENGTH_LONG).show();
} else {
// if it on, animates to the current position
map.animateCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(location.getLatitude(), location.getLongitude()), 15));
return false;
}
return false;
}
});
}
public void TurnOnGps(){
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
protected void onResume() {
// TODO Auto-generated method stub
setUpMapIfNeeded();
super.onResume();
}
private void setUpMapIfNeeded() {
// Do a null check to confirm that we have not already instantiated the
// map.
if (map == null) {
map = ((MapFragment) getFragmentManager().findFragmentById(R.id.map)).getMap();
if (map != null) {
}
}
}
// function that opened an activity to turn on the GPS
private void buildAlertMessageNoGps() {
final AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("GPS is off ")
.setCancelable(true)
.setPositiveButton("Yes",
new DialogInterface.OnClickListener() {
public void onClick(final DialogInterface dialog, final int id) {
startActivity(new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS));
}
})
.setNegativeButton("No", new DialogInterface.OnClickListener() {
public void onClick(final DialogInterface dialog, final int id) {
dialog.cancel();
}
});
final AlertDialog alert = builder.create();
alert.show();
}
@Override
public void onLocationChanged(Location location) {
longitude = location.getLongitude();
latitude = location.getLatitude();
}
}
我的LogCat：
06-04 20:48:44.811: E/AndroidRuntime(11489): FATAL EXCEPTION: main
06-04 20:48:44.811: E/AndroidRuntime(11489): java.lang.RuntimeException: Unable to start activity ComponentInfo{nir.rauch.flantir/nir.rauch.flantir.MainActivity}: java.lang.NullPointerException
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2295)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2349)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.ActivityThread.access$700(ActivityThread.java:159)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1316)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.os.Handler.dispatchMessage(Handler.java:99)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.os.Looper.loop(Looper.java:137)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.ActivityThread.main(ActivityThread.java:5419)
06-04 20:48:44.811: E/AndroidRuntime(11489): at java.lang.reflect.Method.invokeNative(Native Method)
06-04 20:48:44.811: E/AndroidRuntime(11489): at java.lang.reflect.Method.invoke(Method.java:525)
06-04 20:48:44.811: E/AndroidRuntime(11489): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
06-04 20:48:44.811: E/AndroidRuntime(11489): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
06-04 20:48:44.811: E/AndroidRuntime(11489): at dalvik.system.NativeStart.main(Native Method)
06-04 20:48:44.811: E/AndroidRuntime(11489): Caused by: java.lang.NullPointerException
06-04 20:48:44.811: E/AndroidRuntime(11489): at nir.rauch.flantir.MainActivity.onCreate(MainActivity.java:45)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.Activity.performCreate(Activity.java:5372)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
06-04 20:48:44.811: E/AndroidRuntime(11489): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2257)
06-04 20:48:44.811: E/AndroidRuntime(11489): ... 11 more
我已尝试在OnCreate功能中执行if else语句（如果启用了GPS或未启用GPS），但它没有找到该位置。
答案 0 :(得分：4)
final Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
latitude = location.getLatitude(); // <--
longitude = location.getLongitude(); // <--
if (location != null) {
这两行不应该进入if语句吗？