从2个与User Location一起使用的AsyncTask中，只有一个在Java&安卓 [英] from 2 AsyncTask which works with User Location just one works in Java & Android
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问题描述
我有两个可以处理当前用户位置数据的AsyncTask，第一个运行得很好，没有任何问题，但是第二个，停止应用程序运行，应用程序将崩溃.
i have two AsyncTask which works with Current user location data, the first goes well without any problem, but the second, stop the app works and app will crash.
请注意，仅在真实设备中，第一个任务就可以工作，但在虚拟设备中，即使第一个任务也不起作用:|
notice that, just in real device the first task will works but in virtual devices even the first didn't work :|
mainActivity代码:
code of mainActivity:
public class MainActivity extends AppCompatActivity {
Button btnShowLocation;
public static TextView txtTemperature;
public static TextView txtWindSpeed;
public static TextView txtHumidity;
public static TextView txtSummary;
public static TextView txtCityName;
GpsTracker gps;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnShowLocation = (Button)findViewById(R.id.btnupdate);
txtTemperature = (TextView) findViewById(R.id.txtTemperature);
txtWindSpeed = (TextView) findViewById(R.id.txtWindSpeed);
txtHumidity = (TextView) findViewById(R.id.txthumidity);
txtSummary = (TextView) findViewById(R.id.txtSummary);
txtSummary = (TextView) findViewById(R.id.txtCityName);
//find geoLocation
btnShowLocation.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
gps = new GpsTracker(MainActivity.this);
if(gps.canGetLocation()){
Double lat = gps.getLatitude();
Double lng = gps.getLongtitude();
Toast.makeText(getApplicationContext(),
"Your location is -\nLat:"+lat+"\nLng:"+lng,
Toast.LENGTH_LONG).show();
String url = "https://api.forecast.io/forecast/KEY/"+lat+","+lng+"?units=ca";
JsonTask task = new JsonTask(getApplicationContext());
task.execute(url);
String url2 = "http://maps.googleapis.com/maps/api/geocode/json?latlng="+lat+","+lng;
CityNameTask city = new CityNameTask(getApplicationContext());
city.execute(url2);
}
else {
gps.showSettingsAlert();
}
}
});
}
}
第一个正常工作的AsyncTask:
the First AsyncTask which work fine:
class JsonTask extends AsyncTask<String, String, String> {
private Context mContext;
public JsonTask (Context context){
mContext = context;
}
protected void onPreExecute() {
super.onPreExecute();
}
protected String doInBackground(String... params) {
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
StringBuffer buffer = new StringBuffer();
String line = "";
String data = "";
while ((line = reader.readLine()) != null) {
buffer.append(line+"\n");
//Log.d("Response: ", "> " + line); //here u ll get whole response...... :-)
try{
JSONObject jsonObject= new JSONObject(line).getJSONObject("currently");
data=
jsonObject.getString("temperature")+","+
jsonObject.getString("windSpeed")+","+
jsonObject.getString("humidity")+","+
jsonObject.getString("summary");
}
catch(JSONException e)
{
}
}
return data.toString();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
String string = result;
String[] parts = string.split(",");
String temperature = parts[0];
String windSpeed = parts[1];
String humidity = parts[2];
String summary = parts[3];
MainActivity.txtTemperature.setText(temperature);
MainActivity.txtWindSpeed.setText(windSpeed);
MainActivity.txtHumidity.setText(humidity);
MainActivity.txtSummary.setText(summary);
}
}
第二个失败的任务:
class CityNameTask extends AsyncTask<String, String, String> {
private Context mContext;
public CityNameTask (Context context){
mContext = context;
}
protected void onPreExecute() {
super.onPreExecute();
}
protected String doInBackground(String... params) {
HttpURLConnection connection = null;
BufferedReader reader = null;
try {
URL url = new URL(params[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
InputStream stream = connection.getInputStream();
reader = new BufferedReader(new InputStreamReader(stream));
StringBuffer buffer = new StringBuffer();
String line = "";
String data = "";
while ((line = reader.readLine()) != null) {
buffer.append(line+"\n");
}
Log.d("Response: ", "> " + line);
try {
JSONObject jsonRootObject = new JSONObject(line);
JSONArray jsonArray = jsonRootObject.optJSONArray("results");
for(int i=0; i < jsonArray.length(); i++){
JSONObject jsonObject = jsonArray.getJSONObject(i);
data = jsonObject.getString("formatted_address");
}
} catch (JSONException e) {e.printStackTrace();}
return data.toString();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
try {
if (reader != null) {
reader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return null;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
MainActivity.txtCityName.setText(result);
}
}
-logcat:
06-03 22:00:07.998 2804-2804/com.mortezaaghili.havamoon E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.mortezaaghili.havamoon, PID: 2804
java.lang.NullPointerException: Attempt to invoke virtual method 'double android.location.Location.getLatitude()' on a null object reference
at com.mortezaaghili.havamoon.GpsTracker.getLatitude(GpsTracker.java:131)
at com.mortezaaghili.havamoon.MainActivity$1.onClick(MainActivity.java:54)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
再次这是GPSTracker类:
edited again: this is GPSTracker class:
public class GpsTracker extends Service implements LocationListener {
private final Context context;
boolean isGPSEnabled = false;
boolean isNetworkEnabled = false;
boolean canGetLocation = false;
Location location;
Double latitude;
Double longtitude;
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10;
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1;
protected LocationManager locationManager;
public GpsTracker(Context context){
this.context = context;
getLocation();
}
public Location getLocation(){
try {
locationManager = (LocationManager) context.getSystemService(LOCATION_SERVICE);
isGPSEnabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
isNetworkEnabled = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
if (!isGPSEnabled && !isNetworkEnabled){}
else{
this.canGetLocation = true;
if(isNetworkEnabled){
try {
locationManager.requestLocationUpdates(
LocationManager.NETWORK_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES,
this);
if (locationManager != null){
location = locationManager.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if(location != null){
latitude = location.getLatitude();
longtitude = location.getLongitude();
}
}
}
catch (SecurityException e)
{
}
}
if(isGPSEnabled){
if (location == null){
try {
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES,
this);
if (locationManager != null){
location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if(location != null){
latitude = location.getLatitude();
longtitude = location.getLongitude();
}
}
}
catch (SecurityException e)
{
}
}
}
}
}
catch (Exception e){
e.printStackTrace();
}
return location;
}
public void stopUsingGPS(){
if (locationManager != null){
try{
locationManager.removeUpdates(GpsTracker.this);
}
catch(SecurityException e){
}
}
}
public double getLatitude(){
if (locationManager != null){
latitude = location.getLatitude();
}
return latitude;
}
public double getLongtitude(){
if (locationManager != null) {
longtitude = location.getLongitude();
}
return longtitude;
}
public boolean canGetLocation(){
return this.canGetLocation;
}
public void showSettingsAlert(){
AlertDialog.Builder alertDialog = new AlertDialog.Builder(context);
alertDialog.setTitle("GPS is setting");
alertDialog.setMessage("GPS is not enabled. do you want go to settings?");
alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
context.startActivity(intent);
}
});
alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
alertDialog.show();
}
@Override
public void onLocationChanged(Location location) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Nullable
@Override
public IBinder onBind(Intent intent) {
return null;
}
}
推荐答案
似乎是您的 location 变量未从GpsTracker类初始化.因此，当扩展 Service 类并实现 LocationListener 时，您将覆盖名为 getLocation()的方法，该方法应返回 Location 对象，但在您的情况下返回 null .
What it seems like is that your location variable is not initialized from the GpsTracker class.
Therefore when you are extending Service class and implementing LocationListener you would have overridden a method called getLocation(), which should return Location object, but in your case is returning null.
如果您可以只发布该文件的代码，或者自己调试.
If you could just post the code for that file, or debug it on your own.
这篇关于从2个与User Location一起使用的AsyncTask中，只有一个在Java&安卓的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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