NullPointerException导致Android应用崩溃

Question

I am getting weather info in my app and had it working. Now I am getting a null pointer exception and I'm not sure why, especially since it was working and I haven't changed any of this code.

package com.kentuckyfarmbureau.kyfb;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.location.Location;
import android.location.LocationManager;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.inputmethod.EditorInfo;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TextView.OnEditorActionListener;

public class WeatherLocation extends Activity
{
    EditText locationText;
    TextView label;
    Button getWeather;
    String enteredText;
    String url = "http://api.worldweatheronline.com/free/v1/weather.ashx?q=%s&format=json&num_of_days=5&key=37a5fj42xpyptvjgkhrx5rwu";
    String newURL;
    String currentLocationText;
    LocationManager lm;
    Location location;
    double longitude;
    double latitude;
    String longString;
    String latString;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.weatherlocation);

        locationText = (EditText) findViewById(R.id.locationTextView);
        label = (TextView) findViewById(R.id.label);
        getWeather = (Button) findViewById(R.id.showWeather);

        locationText.setText("Current Location");

         lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
         location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
         longitude = location.getLongitude();
         latitude = location.getLatitude();
         longString = String.valueOf(longitude);
         latString = String.valueOf(latitude);
         currentLocationText = (latString + "+" + longString);
         enteredText = currentLocationText;

         newURL = String.format(url, enteredText);

        locationText.setOnEditorActionListener(new OnEditorActionListener()
        {
             @Override
            public boolean onEditorAction(TextView v, int actionId, KeyEvent event) 
            {
                 boolean handled = false;
                 if (actionId == EditorInfo.IME_ACTION_DONE)
                 {
                     if(locationText.getText().toString().equals("Current Location"))
                     {
                         lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
                         location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
                         longitude = location.getLongitude();
                         latitude = location.getLatitude();
                         longString = String.valueOf(longitude);
                         latString = String.valueOf(latitude);
                         currentLocationText = (latString + "+" + longString);
                         enteredText = currentLocationText;
                     }
                     else
                     {
                         enteredText = locationText.getText().toString();
                         enteredText = enteredText.replaceAll(" ", "+"); 
                     }
                     System.out.println(enteredText);

                    // hide the virtual keyboard
                    InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
                    imm.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 
                                              InputMethodManager.RESULT_UNCHANGED_SHOWN);

                    newURL = String.format(url, enteredText);
                    System.out.println("Formatted URL: " + newURL);
                     handled = true;
                 }

                 return handled;
            }
        });

        // Get Weather button
        getWeather.setOnClickListener(new View.OnClickListener()
        {
            public void onClick(View v)
            {
                Intent weather = new Intent(WeatherLocation.this, Weather.class);
                weather.putExtra("INTENT_KEY_URL", newURL);
                weather.putExtra("CURRENT_LOCATION", locationText.getText().toString());
                startActivity(weather);
            }
        });
    }
}

The problem seems to be line 48, longitude = location.getLongitude();

Answer 1

If line 48 is causing the issues, then most likely your location is null. This can be null if you call getLastKnownLocation() while the provider is disabled as noted in the android documentation.

Answer 2

I fixed this by adding a location listener.

final LocationListener locationListener = new LocationListener()
     {


    @Override
             public void onLocationChanged(Location currentLocation)
             {
                 latitude = currentLocation.getLatitude();
                 longitude = currentLocation.getLongitude();
             }
             public void onProviderDisabled(String provider) 
             {

             }
             public void onProviderEnabled(String provider) 
             {

             }
             public void onStatusChanged(String provider, int status, Bundle extras) 
             {

             }
         };

And adding:

lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 100, 1, locationListener);