我有两个与当前用户位置数据一起使用的AsyncTask，第一个没有任何问题，但第二个，停止应用程序工作，应用程序将崩溃。
请注意，只是在真实设备中，第一个任务才有效，但在虚拟设备中，即使是第一个任务也无效：|
mainActivity的代码：
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AsyncTask工作正常：
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);
}
}
- 编辑：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)
再次编辑： 这是GPSTracker类：
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;
}
}
答案 0 :(得分：1)
看起来您的location变量未从GpsTracker类初始化。
因此，当您扩展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{{1} }}
如果你可以发布该文件的代码，或者自己调试它。
答案 1 :(得分：0)
可能你的GpsTracker类必须包含以下内容：
public double getLatitude() {
if(location != null) { // here must be checked if location is available and it's not null, coz now you probably get crash coz this has not been checked
latitude = location.getLatitude();
}
return latitude;
}
答案 2 :(得分：0)
为了避免获取Null Locations，您需要使用google play locations API 这是谷歌推荐的。
同时尝试
String line = "";
String data = "";
while ((line = reader.readLine()) != null) {
buffer.append(line+"\n");
}
在此循环结束时，line对象为null 因此，在一些变量中保存最后一行元素的副本 然后在其上应用以下代码。
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");
}
答案 3 :(得分：0)
堆栈跟踪的相关部分是：
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)
提到破碎的代码：
public double getLatitude(){
if (locationManager != null){
latitude = location.getLatitude();
}
return latitude;
}
您正在检查空locationManager，但随后调用location上的某个方法，该方法可能在getLocation()设置方法中的大尝试/抓住吞咽时无效在GPSTracker构造函数中。
检查location null：
public double getLatitude(){
if (location != null){
latitude = location.getLatitude();
}
return latitude;
}