我咨询了很多答案，但没有得到解决方案。当我禁用 GPS 时出现此错误。如果启用了 GPS，则应用程序运行正常。如果我最初或在运行过程中禁用 GPS，则应用程序崩溃。当 GPS 被禁用时，我想在这里弹出警报对话框。
MainActivity.java
package com.project.locationinfofinder;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.json.JSONObject;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.DialogInterface.OnClickListener;
import android.graphics.Color;
import android.location.Criteria;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.util.Log;
import android.view.Menu;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.GoogleMap.OnMapClickListener;
import com.google.android.gms.maps.SupportMapFragment;
import com.google.android.gms.maps.model.BitmapDescriptorFactory;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;
import com.google.android.gms.maps.model.PolylineOptions;
public class MainActivity extends FragmentActivity implements LocationListener {
GoogleMap mGoogleMap;
ArrayList<LatLng> mMarkerPoints;
double mLatitude=0;
double mLongitude=0;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Getting Google Play availability status
int status = GooglePlayServicesUtil.isGooglePlayServicesAvailable(getBaseContext());
if(status!=ConnectionResult.SUCCESS){ // Google Play Services are not available
int requestCode = 10;
Dialog dialog = GooglePlayServicesUtil.getErrorDialog(status, this, requestCode);
dialog.show();
}else { // Google Play Services are available
// Initializing
mMarkerPoints = new ArrayList<LatLng>();
// Getting reference to SupportMapFragment of the activity_main
SupportMapFragment fm = (SupportMapFragment)getSupportFragmentManager().findFragmentById(R.id.map);
// Getting Map for the SupportMapFragment
mGoogleMap = fm.getMap();
// Enable MyLocation Button in the Map
mGoogleMap.setMyLocationEnabled(true);
// Getting LocationManager object from System Service LOCATION_SERVICE
LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
// Creating a criteria object to retrieve provider
Criteria criteria = new Criteria();
// Getting the name of the best provider
String provider = locationManager.getBestProvider(criteria, true);
// Getting Current Location From GPS
Location location = locationManager.getLastKnownLocation(provider);
if(location!=null){
onLocationChanged(location);
}
locationManager.requestLocationUpdates(provider, 20000, 0, this);
// Setting onclick event listener for the map
mGoogleMap.setOnMapClickListener(new OnMapClickListener() {
@Override
public void onMapClick(LatLng point) {
// Already map contain destination location
if(mMarkerPoints.size()>1){
FragmentManager fm = getSupportFragmentManager();
mMarkerPoints.clear();
mGoogleMap.clear();
LatLng startPoint = new LatLng(mLatitude, mLongitude);
drawMarker(startPoint);
}
drawMarker(point);
// Checks, whether start and end locations are captured
if(mMarkerPoints.size() >= 2){
LatLng origin = mMarkerPoints.get(0);
LatLng dest = mMarkerPoints.get(1);
// Getting URL to the Google Directions API
String url = getDirectionsUrl(origin, dest);
DownloadTask downloadTask = new DownloadTask();
// Start downloading json data from Google Directions API
downloadTask.execute(url);
}
}
});
}
}
private String getDirectionsUrl(LatLng origin,LatLng dest){
// Origin of route
String str_origin = "origin="+origin.latitude+","+origin.longitude;
// Destination of route
String str_dest = "destination="+dest.latitude+","+dest.longitude;
// Sensor enabled
String sensor = "sensor=false";
// Building the parameters to the web service
String parameters = str_origin+"&"+str_dest+"&"+sensor;
// Output format
String output = "json";
// Building the url to the web service
String url = "https://maps.googleapis.com/maps/api/directions/"+output+"?"+parameters;
return url;
}
/** A method to download json data from url */
private String downloadUrl(String strUrl) throws IOException{
String data = "";
InputStream iStream = null;
HttpURLConnection urlConnection = null;
try{
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while( ( line = br.readLine()) != null){
sb.append(line);
}
data = sb.toString();
br.close();
}catch(Exception e){
Log.d("Exception while downloading url", e.toString());
}finally{
iStream.close();
urlConnection.disconnect();
}
return data;
}
/** A class to download data from Google Directions URL */
private class DownloadTask extends AsyncTask<String, Void, String>{
// Downloading data in non-ui thread
@Override
protected String doInBackground(String... url) {
// For storing data from web service
String data = "";
try{
// Fetching the data from web service
data = downloadUrl(url[0]);
}catch(Exception e){
Log.d("Background Task",e.toString());
}
return data;
}
// Executes in UI thread, after the execution of
// doInBackground()
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
ParserTask parserTask = new ParserTask();
// Invokes the thread for parsing the JSON data
parserTask.execute(result);
}
}
/** A class to parse the Google Directions in JSON format */
private class ParserTask extends AsyncTask<String, Integer, List<List<HashMap<String,String>>> >{
// Parsing the data in non-ui thread
@Override
protected List<List<HashMap<String, String>>> doInBackground(String... jsonData) {
JSONObject jObject;
List<List<HashMap<String, String>>> routes = null;
try{
jObject = new JSONObject(jsonData[0]);
DirectionsJSONParser parser = new DirectionsJSONParser();
// Starts parsing data
routes = parser.parse(jObject);
}catch(Exception e){
e.printStackTrace();
}
return routes;
}
// Executes in UI thread, after the parsing process
@Override
protected void onPostExecute(List<List<HashMap<String, String>>> result) {
ArrayList<LatLng> points = null;
PolylineOptions lineOptions = null;
// Traversing through all the routes
for(int i=0;i<result.size();i++){
points = new ArrayList<LatLng>();
lineOptions = new PolylineOptions();
// Fetching i-th route
List<HashMap<String, String>> path = result.get(i);
// Fetching all the points in i-th route
for(int j=0;j<path.size();j++){
HashMap<String,String> point = path.get(j);
double lat = Double.parseDouble(point.get("lat"));
double lng = Double.parseDouble(point.get("lng"));
LatLng position = new LatLng(lat, lng);
points.add(position);
}
// Adding all the points in the route to LineOptions
lineOptions.addAll(points);
lineOptions.width(2);
lineOptions.color(Color.RED);
}
// Drawing polyline in the Google Map for the i-th route
mGoogleMap.addPolyline(lineOptions);
}
}
@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;
}
private void drawMarker(LatLng point){
mMarkerPoints.add(point);
// Creating MarkerOptions
MarkerOptions options = new MarkerOptions();
// Setting the position of the marker
options.position(point);
//For the start location, the color of marker is GREEN and
// for the end location, the color of marker is RED.
if(mMarkerPoints.size()==1){
options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_GREEN));
}else if(mMarkerPoints.size()==2){
options.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED));
}
// Add new marker to the Google Map Android API V2
mGoogleMap.addMarker(options);
}
@Override
public void onLocationChanged(Location location) {
// Draw the marker, if destination location is not set
if(mMarkerPoints.size() < 2){
mLatitude = location.getLatitude();
mLongitude = location.getLongitude();
LatLng point = new LatLng(mLatitude, mLongitude);
mGoogleMap.moveCamera(CameraUpdateFactory.newLatLng(point));
mGoogleMap.animateCamera(CameraUpdateFactory.zoomTo(12));
drawMarker(point);
}
}
@Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setTitle("GPS is disabled");
builder.setCancelable(false);
builder.setPositiveButton("Enable GPS", new OnClickListener() {
@Override
public void onClick(DialogInterface dailog, int which) {
// TODO Auto-generated method stub
Intent StartGPS = new Intent(
android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
startActivity(StartGPS);
}
});
builder.setNegativeButton("Cancel", new OnClickListener() {
@Override
public void onClick(DialogInterface dailog, int which) {
// TODO Auto-generated method stub
dailog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}
@Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
}
日志猫
08-09 15:42:21.718: E/AndroidRuntime(21516): FATAL EXCEPTION: main
08-09 15:42:21.718: E/AndroidRuntime(21516): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.project.locationinfofinder/com.project.locationinfofinder.MainActivity}: java.lang.IllegalArgumentException: provider==null
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.os.Handler.dispatchMessage(Handler.java:99)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.os.Looper.loop(Looper.java:130)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.app.ActivityThread.main(ActivityThread.java:3687)
08-09 15:42:21.718: E/AndroidRuntime(21516): at java.lang.reflect.Method.invokeNative(Native Method)
08-09 15:42:21.718: E/AndroidRuntime(21516): at java.lang.reflect.Method.invoke(Method.java:507)
08-09 15:42:21.718: E/AndroidRuntime(21516): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
08-09 15:42:21.718: E/AndroidRuntime(21516): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
08-09 15:42:21.718: E/AndroidRuntime(21516): at dalvik.system.NativeStart.main(Native Method)
08-09 15:42:21.718: E/AndroidRuntime(21516): Caused by: java.lang.IllegalArgumentException: provider==null
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.location.LocationManager.requestLocationUpdates(LocationManager.java:441)
08-09 15:42:21.718: E/AndroidRuntime(21516): at com.project.locationinfofinder.MainActivity.onCreate(MainActivity.java:105)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-09 15:42:21.718: E/AndroidRuntime(21516): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
08-09 15:42:21.718: E/AndroidRuntime(21516): ... 11 more