我正在使用该位置，但现在每当我单击应用程序上的按钮时，我都会不断收到 nullPointerException。该按钮刷新显示的位置。位置以纬度、经度、街道地址、城市、国家和邮政地址显示。这是下面的代码。
package com.example.metrorails;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
CurrentPosition currentPosition;
String address;
String city;
String country;
String postalCode;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button refresh;
refresh = (Button)findViewById(R.id.refresh);
refresh.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
currentPosition = new CurrentPosition(MainActivity.this);
TextView showresults = (TextView) findViewById(R.id.show_results);
showresults.setTextSize(20);
if(currentPosition.canGetLocation()){
double latitude = currentPosition.getLatitude();
double longitude = currentPosition.getLongitude();
showresults.setText("current latitude: "+latitude +"\n current longitude: "+longitude+
"\n Address is: " +currentPosition.getAddress() + "\n city is: "+currentPosition.getCity()+
"\n Current Country is: "+currentPosition.getCountry() +"\n Area Code : "+currentPosition.getPostalCode());
}else{
// can't get location
// GPS or Network is not enabled
// Ask user to enable GPS/network in settings
currentPosition.showSettingsAlert();
}
}
});
}
@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;
}
}
我仍然有这个程序的问题。这是下面的logcat。
09-09 18:56:52.393: E/AndroidRuntime(1882): FATAL EXCEPTION: main
09-09 18:56:52.393: E/AndroidRuntime(1882): java.lang.NullPointerException
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.content.ContextWrapper.getPackageName(ContextWrapper.java:135)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.location.GeocoderParams. <init>(GeocoderParams.java:50)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.location.Geocoder.<init>(Geocoder.java:83)
09-09 18:56:52.393: E/AndroidRuntime(1882): at com.example.metrorails.CurrentPosition.<init>(CurrentPosition.java:71)
09-09 18:56:52.393: E/AndroidRuntime(1882): at com.example.metrorails.MainActivity$1.onClick(MainActivity.java:31)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.view.View.performClick(View.java:4240)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.view.View$PerformClick.run(View.java:17721)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.os.Handler.handleCallback(Handler.java:730)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.os.Handler.dispatchMessage(Handler.java:92)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.os.Looper.loop(Looper.java:137)
09-09 18:56:52.393: E/AndroidRuntime(1882): at android.app.ActivityThread.main(ActivityThread.java:5103)
09-09 18:56:52.393: E/AndroidRuntime(1882): at java.lang.reflect.Method.invokeNative(Native Method)
09-09 18:56:52.393: E/AndroidRuntime(1882): at java.lang.reflect.Method.invoke(Method.java:525)
09-09 18:56:52.393: E/AndroidRuntime(1882): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
09-09 18:56:52.393: E/AndroidRuntime(1882): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
09-09 18:56:52.393: E/AndroidRuntime(1882): at dalvik.system.NativeStart.main(Native Method)
09-09 18:57:01.512: I/Process(1882): Sending signal. PID: 1882 SIG: 9
下面是 CurrentPosition 类。
package com.example.metrorails;
import java.io.IOException;
import java.util.List;
import java.util.Locale;
import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Address;
import android.location.Geocoder;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.provider.Settings;
import android.util.Log;
public class CurrentPosition extends Service implements LocationListener {
private final Context mContext;
// flag for GPS status
boolean isGPSEnabled = false;
// flag for network status
boolean isNetworkEnabled = false;
// flag for GPS status
boolean canGetLocation = false;
Location location; // location
double latitude; // latitude
double longitude; // longitude
public static String address;
public static String city;
private static String country;
private static String postalCode;
// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters
// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute
// Declaring a Location Manager
protected LocationManager locationManager;
public String getAddress(){
return address;
}
public String getCity(){
return city;
}
public String getCountry(){
return country;
}
public String getPostalCode(){
return postalCode;
}
public CurrentPosition(Context context) {
this.mContext = context;
getLocation();
}
public void getLocation() {
try {
locationManager = (LocationManager) mContext
.getSystemService(LOCATION_SERVICE);
// getting GPS status
isGPSEnabled = locationManager
.isProviderEnabled(LocationManager.GPS_PROVIDER);
// getting network status
isNetworkEnabled = locationManager
.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
if (!isGPSEnabled && !isNetworkEnabled) {
// no network provider is enabled
} else {
this.canGetLocation = true;
if (isNetworkEnabled) {
locationManager.requestLocationUpdates(
LocationManager.NETWORK_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("Network", "Network");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
// if GPS Enabled get lat/long using GPS Services
if (isGPSEnabled) {
if (location == null) {
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("GPS Enabled", "GPS Enabled");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
Geocoder geocode = new Geocoder(this, Locale.getDefault());
List<Address> addresses;
try {
addresses = geocode.getFromLocation(latitude,longitude, 1);
this.address = addresses.get(0).getAddressLine(0);
this.city = addresses.get(0).getAddressLine(1);
this.country = addresses.get(0).getAddressLine(2);
this.postalCode = addresses.get(0).getPostalCode();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
}} catch (Exception e) {
e.printStackTrace();
}
this.location = location;
}
/**
* Stop using GPS listener
* Calling this function will stop using GPS in your app
* */
public void stopUsingGPS(){
if(locationManager != null){
locationManager.removeUpdates(CurrentPosition.this);
}
}
/**
* Function to get latitude
* */
public double getLatitude(){
if(location != null){
latitude = location.getLatitude();
}
// return latitude
return latitude;
}
/**
* Function to get longitude
* */
public double getLongitude(){
if(location != null){
longitude = location.getLongitude();
}
// return longitude
return longitude;
}
/**
* Function to check GPS/wifi enabled
* @return boolean
* */
public boolean canGetLocation() {
return this.canGetLocation;
}
/**
* Function to show settings alert dialog
* On pressing Settings button will lauch Settings Options
* */
public void showSettingsAlert(){
AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
// Setting Dialog Title
alertDialog.setTitle("GPS is settings");
// Setting Dialog Message
alertDialog.setMessage("GPS is not enabled. Do you want to go to settings menu?");
// On pressing Settings button
alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
mContext.startActivity(intent);
}
});
// on pressing cancel button
alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
// Showing Alert Message
alertDialog.show();
}
@Override
public void onLocationChanged(Location location) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public IBinder onBind(Intent arg0) {
return null;
}