當互聯網連接不可用時，應用程序崩潰

Question

當應用程序運行並且連接關閉時，我們正在面對我們的應用程序的一個特殊問題，它工作正常。然而，當我們嘗試搜索某個特定的地方時，它會崩潰。請參考下面的代碼，我們使用谷歌地圖API -

public class MainActivity extends AppCompatActivity implements  OnMapReadyCallback, 
    GoogleApiClient.ConnectionCallbacks,GoogleApiClient.OnConnectionFailedListener, 
    LocationListener, AdapterView.OnItemClickListener { 

private GoogleMap mMap; 
    GoogleApiClient mGoogleApiClient; 
    Location mLastLocation; 
    Marker mCurrLocationMarker,FindMarker; 
    LocationRequest mLocationRequest; 
    AutoCompleteTextView atvPlaces; 
    DownloadTask placesDownloadTask; 
    DownloadTask placeDetailsDownloadTask; 
    ParserTask placesParserTask; 
    ParserTask placeDetailsParserTask; 
    LatLng latLng; 
    final int PLACES = 0; 
    final int PLACES_DETAILS = 1; 
    ListView lv; 
    ImageButton remove; 
    private boolean exit = false; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    // Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); 
    // setSupportActionBar(toolbar); 



    if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { 
    checkLocationPermission(); 
    } 

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab); 
    fab.setOnClickListener(new View.OnClickListener() { 

    @Override 
    public void onClick(View view) { 
    onLocationChanged(mLastLocation); 
    } 
    }); 

    SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager() 
    .findFragmentById(R.id.map); 
    mapFragment.getMapAsync(this); 


    AdView adView = (AdView)findViewById(R.id.addview); 
    AdRequest adRequest = new AdRequest.Builder().build(); 

    adView.loadAd(adRequest); 

    remove = (ImageButton)findViewById(R.id.place_autocomplete_clear_button); 

    // Getting a reference to the AutoCompleteTextView 
    atvPlaces = (AutoCompleteTextView) findViewById(R.id.id_search_EditText); 
    atvPlaces.setThreshold(1); 

    // Adding textchange listener 
    atvPlaces.addTextChangedListener(new TextWatcher() { 

    @Override 
    public void onTextChanged(CharSequence s, int start, int before, int count) { 
    // Creating a DownloadTask to download Google Places matching "s" 
    placesDownloadTask = new DownloadTask(PLACES); 

    // Getting url to the Google Places Autocomplete api 
     String url = getAutoCompleteUrl(s.toString()); 

    // Start downloading Google Places 
    // This causes to execute doInBackground() of DownloadTask class 

     placesDownloadTask.execute(url); 


     if (!atvPlaces.getText().toString().equals("")){ 
      lv.setVisibility(View.VISIBLE); 
      remove.setVisibility(View.VISIBLE); 
     }else { 
      lv.setVisibility(View.GONE); 
      remove.setVisibility(View.GONE); 
     } 


    } 

    @Override 
    public void beforeTextChanged(CharSequence s, int start, int count, 
    int after) { 
    // TODO Auto-generated method stub 
    } 

    @Override 
    public void afterTextChanged(Editable s) { 
    // TODO Auto-generated method stub 
    } 
    }); 


    lv=(ListView)findViewById(R.id.list); 

    lv.setOnItemClickListener(this); 

    // for enter button search hide key board and search using by enter button.. 
    atvPlaces.setOnEditorActionListener(new AutoCompleteTextView.OnEditorActionListener() { 

    public boolean onEditorAction(TextView v, int actionId, 
            KeyEvent event) { 
     if (actionId == EditorInfo.IME_ACTION_SEARCH) { 

      String location = atvPlaces.getText().toString(); 
      if (location != null && !location.equals("")) { 
       new GeocoderTask().execute(location); 

      } 
      lv.setVisibility(View.GONE); 
      InputMethodManager im = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE); 
      im.hideSoftInputFromWindow(atvPlaces.getWindowToken(), 0); 
      return true; 
     } 
     return false; 
    } 
}); 


    setListenerOnWidget(); 
    checkLocation(); 
} 

// location access allow or not 
private void checkLocation() { 

    LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 
    LocationManager locationManager = null; 
    boolean location_enabled = false; 
    boolean network_enabled = false; 

    try { 
     location_enabled = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER); 
    } catch (Exception ex){} 


    try { 
     network_enabled = lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER); 
    } catch(Exception ex) {} 

    if (!location_enabled && !network_enabled){ 
     AlertDialog.Builder dialog = new AlertDialog.Builder(MainActivity.this); 
     dialog.setMessage("Location Not Enabled"); 
     dialog.setTitle("Check Location Access"); 
     dialog.setCancelable(false); 
     dialog.setPositiveButton("Allow", new DialogInterface.OnClickListener() { 

      @Override 
      public void onClick(DialogInterface dialog, int which) { 
       //this will navigate user to the device location settings screen 
       Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS); 
       startActivity(intent); 
      } 
     }); 
     AlertDialog alert = dialog.create(); 
     alert.show(); 
    } 
} 

private void setListenerOnWidget() { 
    View.OnClickListener listener = new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
     atvPlaces.setText(""); 
     } 
    }; 
    remove.setOnClickListener(listener); 
} 

@Override 
public void onBackPressed() { 
    if(exit){ 
     finish(); 
    }else { 
     Toast.makeText(this, "Tap Back again to Exit.", 
       Toast.LENGTH_SHORT).show(); 
     exit = true; 
     new Handler().postDelayed(new Runnable() { 
      @Override 
      public void run() { 
       exit = false; 
      } 
     }, 3 * 1000); 

    } 
    } 


@Override 
public void onItemClick (AdapterView <?> adapterView, View view,int i, long l){ 
    //ListView lv = (ListView) adapterView; 
    SimpleAdapter adapter = (SimpleAdapter) adapterView.getAdapter(); 

    HashMap<String, String> hm = (HashMap<String, String>) adapter.getItem(i); 

    // Creating a DownloadTask to download Places details of the selected place 
    placeDetailsDownloadTask = new DownloadTask(PLACES_DETAILS); 

    // Getting url to the Google Places details api 
    String url = getPlaceDetailsUrl(hm.get("reference")); 

    // Start downloading Google Place Details 
    // This causes to execute doInBackground() of DownloadTask class 
    placeDetailsDownloadTask.execute(url); 

    InputMethodManager inputManager = (InputMethodManager) 
      getSystemService(Context.INPUT_METHOD_SERVICE); 

    inputManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 
      InputMethodManager.HIDE_NOT_ALWAYS); 

    String str = ((TextView) view.findViewById(R.id.place_name)).getText().toString(); 
    Toast.makeText(this,str, Toast.LENGTH_SHORT).show(); 
    //atvPlaces.setText(str.replace(' ',',')); 
    atvPlaces.setText(str); 

    lv.setVisibility(view.GONE); 


} 



private String getPlaceDetailsUrl(String ref) { 
    // Obtain browser key from https://code.google.com/apis/console 
    String key = "key=*******************************************"; 

    // reference of place 
    String reference = "reference=" + ref; 

    // Sensor enabled 
    String sensor = "sensor=false"; 

    // Building the parameters to the web service 
    String parameters = reference + "&" + sensor + "&" + key; 

    // Output format 
    String output = "json"; 

    // Building the url to the web service 
    String url = "https://maps.googleapis.com/maps/api/place/details/" + output + "?" + parameters; 

    return url; 
    } 

private String getAutoCompleteUrl(String place) { 
    // Obtain browser key from https://code.google.com/apis/console 
    String key = "key=**********************************"; 

    // place to be be searched 
    String input = "input=" + place; 

    // place type to be searched 
    String types = "types=geocode"; 

    // Sensor enabled 
    String sensor = "sensor=false"; 

    // Building the parameters to the web service 
    String parameters = input + "&" + types + "&" + sensor + "&" + key; 

    // Output format 
    String output = "json"; 

    // Building the url to the web service 
    String url = "https://maps.googleapis.com/maps/api/place/autocomplete/" + output + "?" + parameters; 

    url = url.replaceAll(" ", "%20"); 
    return 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; 
    } 

    public static final int MY_PERMISSIONS_REQUEST_LOCATION = 99; 

public boolean checkLocationPermission() { 
    if (ContextCompat.checkSelfPermission(this, 
    Manifest.permission.ACCESS_FINE_LOCATION) 
    != PackageManager.PERMISSION_GRANTED) { 

    if (ActivityCompat.shouldShowRequestPermissionRationale(this, 
    Manifest.permission.ACCESS_FINE_LOCATION)) { 

    ActivityCompat.requestPermissions(this, 
    new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 
    MY_PERMISSIONS_REQUEST_LOCATION); 
    } else { 
    ActivityCompat.requestPermissions(this, 
    new String[]{Manifest.permission.ACCESS_FINE_LOCATION}, 
    MY_PERMISSIONS_REQUEST_LOCATION); 
    } 
    return false; 
    } else { 
    return true; 
    } 

    } 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_main, menu); 
    return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
    return true; 
    } 

    return super.onOptionsItemSelected(item); 
    } 

    @Override 
    public void onConnected(@Nullable Bundle bundle) { 
    mLocationRequest = new LocationRequest(); 
    //mLocationRequest.setInterval(1000); 
    //mLocationRequest.setFastestInterval(1000); 
    mLocationRequest.setPriority(LocationRequest.PRIORITY_BALANCED_POWER_ACCURACY); 

    if (ContextCompat.checkSelfPermission(this, 
    Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) { 
    LocationServices.FusedLocationApi.requestLocationUpdates(mGoogleApiClient, mLocationRequest, this); 
    } 
    } 

    @Override 
    public void onConnectionSuspended(int i) { 

    } 

    @Override 
    public void onLocationChanged(Location location) { 
mLastLocation = location; 
if(mCurrLocationMarker != null){ 
    mCurrLocationMarker.remove(); 
} 

LatLng latLng = new LatLng(location.getLatitude(),location.getLongitude()); 
MarkerOptions markerOption = new MarkerOptions(); 
markerOption.position(latLng); 
markerOption.title("Current Position"); 
markerOption.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_MAGENTA)); 
mCurrLocationMarker = mMap.addMarker(markerOption); 
Toast.makeText(this,"Location changed",Toast.LENGTH_SHORT).show(); 
CameraPosition cameraPosition = new CameraPosition.Builder().target(latLng).zoom(13).build(); 
mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition)); 

if(mGoogleApiClient != null){ 
    LocationServices.FusedLocationApi.removeLocationUpdates(mGoogleApiClient,this); 
} 

    loadNearByPlaces(location.getLatitude(), location.getLongitude()); 
    } 

    @Override 
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) { 

    } 

    @Override 
    public void onMapReady(GoogleMap googleMap) { 

    mMap = googleMap; 

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { 
    if (ContextCompat.checkSelfPermission(this, 
    android.Manifest.permission.ACCESS_FINE_LOCATION) 
    == PackageManager.PERMISSION_GRANTED) { 
    buildGoogleApiClient(); 
    mMap.setMyLocationEnabled(true); 

    } 
    } else { 
    buildGoogleApiClient(); 
    mMap.setMyLocationEnabled(true); 
    } 

    } 

    protected synchronized void buildGoogleApiClient() { 
    mGoogleApiClient = new GoogleApiClient.Builder(this) 
    .addConnectionCallbacks(this) 
    .addOnConnectionFailedListener(this) 
    .addApi(LocationServices.API) 
    .build(); 
    mGoogleApiClient.connect(); 
    } 

    @Override 
    public void onRequestPermissionsResult(int requestCode, 
    String permissions[], int[] grantResult) { 
    switch (requestCode) { 
    case MY_PERMISSIONS_REQUEST_LOCATION: { 

    if (grantResult.length > 0 
    && grantResult[0] == PackageManager.PERMISSION_GRANTED) { 
    if (ContextCompat.checkSelfPermission(this, 
    Manifest.permission.ACCESS_FINE_LOCATION) 
    == PackageManager.PERMISSION_GRANTED) { 
    if (mGoogleApiClient == null) { 
    buildGoogleApiClient(); 
    } 
    mMap.setMyLocationEnabled(true); 
    } 

    } else { 
    Toast.makeText(this, "permisison denied", Toast.LENGTH_LONG).show(); 
    } 
    return; 
    } 

    } 
    } 

    private void loadNearByPlaces(double latitude, double longitude) { 
    //YOU Can change this type at your own will, e.g hospital, cafe, restaurant.... and see how it all works 
    String type = "atm"; 
    StringBuilder googlePlacesUrl = 
    new StringBuilder("https://maps.googleapis.com/maps/api/place/nearbysearch/json?"); 
    googlePlacesUrl.append("location=").append(latitude).append(",").append(longitude); 
    googlePlacesUrl.append("&radius=").append(PROXIMITY_RADIUS); 
    googlePlacesUrl.append("&types=").append(type); 
    googlePlacesUrl.append("&sensor=true"); 
    googlePlacesUrl.append("&key=" + GOOGLE_BROWSER_API_KEY); 

    JsonObjectRequest request = new JsonObjectRequest(googlePlacesUrl.toString(), 
    new Response.Listener<JSONObject>() { 
    @Override 
    public void onResponse(JSONObject result) { 

    Log.i(TAG, "onResponse: Result= " + result.toString()); 
    parseLocationResult(result); 
    } 
    }, 
    new Response.ErrorListener() { 
    @Override 
    public void onErrorResponse(VolleyError error) { 
    Log.e(TAG, "onErrorResponse: Error= " + error); 
    Log.e(TAG, "onErrorResponse: Error= " + error.getMessage()); 
    } 
    }); 

    AppController.getInstance().addToRequestQueue(request); 
    } 

    private void parseLocationResult(JSONObject result) { 

    String id, place_id, placeName = null, reference, icon, vicinity = null; 
    double latitude, longitude; 

    try { 
    JSONArray jsonArray = result.getJSONArray("results"); 

    if (result.getString(STATUS).equalsIgnoreCase(OK)) { 

    //mMap.clear(); 

    for (int i = 0; i < jsonArray.length(); i++) { 
    JSONObject place = jsonArray.getJSONObject(i); 

    id = place.getString(ATM_ID); 
    place_id = place.getString(PLACE_ID); 
    if (!place.isNull(NAME)) { 
    placeName = place.getString(NAME); 
    } 
    if (!place.isNull(VICINITY)) { 
    vicinity = place.getString(VICINITY); 
    } 
    latitude = place.getJSONObject(GEOMETRY).getJSONObject(LOCATION) 
    .getDouble(LATITUDE); 
    longitude = place.getJSONObject(GEOMETRY).getJSONObject(LOCATION) 
    .getDouble(LONGITUDE); 
    reference = place.getString(REFERENCE); 
    icon = place.getString(ICON); 

    MarkerOptions markerOptions = new MarkerOptions(); 
    LatLng latLng = new LatLng(latitude, longitude); 
    markerOptions.position(latLng); 
    markerOptions.title(placeName); 
     markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_BLUE)); 
     markerOptions.snippet(vicinity); 
    mMap.addMarker(markerOptions); 

     mMap.setInfoWindowAdapter(new GoogleMap.InfoWindowAdapter() { 

      @Override 
      public View getInfoWindow(Marker arg0) { 

       return null; 
      } 

      @Override 
      public View getInfoContents(Marker marker) { 
       View myContentsView = getLayoutInflater().inflate(R.layout.marker, null); 
       TextView tvTitle = ((TextView)myContentsView.findViewById(R.id.title)); 
       tvTitle.setText(marker.getTitle()); 
       TextView tvSnippet = ((TextView)myContentsView.findViewById(R.id.snippet)); 
       tvSnippet.setText(marker.getSnippet()); 
       return myContentsView; 
      } 
     }); 

    } 

    Toast.makeText(getBaseContext(), jsonArray.length() + " ATM_FOUND!", 
    Toast.LENGTH_SHORT).show(); 
    } else if (result.getString(STATUS).equalsIgnoreCase(ZERO_RESULTS)) { 
    Toast.makeText(getBaseContext(), "No ATM found in 5KM radius!!!", 
    Toast.LENGTH_LONG).show(); 
    } 

    } catch (JSONException e) { 

    e.printStackTrace(); 
    Log.e(TAG, "parseLocationResult: Error=" + e.getMessage()); 
    } 
    } 

private class DownloadTask extends AsyncTask<String, Void, String> { 
private int downloadType = 0; 

// Constructor 
public DownloadTask(int type) { 
    this.downloadType = type; 
} 

@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; 
} 

@Override 
protected void onPostExecute(String result) { 
    super.onPostExecute(result); 

    switch (downloadType) { 
     case PLACES: 
      // Creating ParserTask for parsing Google Places 
      placesParserTask = new ParserTask(PLACES); 

      // Start parsing google places json data 
      // This causes to execute doInBackground() of ParserTask class 
      placesParserTask.execute(result); 

      break; 

     case PLACES_DETAILS: 
      // Creating ParserTask for parsing Google Places 
      placeDetailsParserTask = new ParserTask(PLACES_DETAILS); 

      // Starting Parsing the JSON string 
      // This causes to execute doInBackground() of ParserTask class 
      placeDetailsParserTask.execute(result); 
    } 
    } 
} 

    private class ParserTask extends AsyncTask<String, Integer, List<HashMap<String, String>>> { 

int parserType = 0; 

public ParserTask(int type) { 
    this.parserType = type; 
} 

@Override 
protected List<HashMap<String, String>> doInBackground(String... jsonData) { 

    JSONObject jObject; 
    List<HashMap<String, String>> list = null; 

    try { 
     jObject = new JSONObject(jsonData[0]); 

     switch (parserType) { 
      case PLACES: 
       PlaceJSONParser placeJsonParser = new PlaceJSONParser(); 
       // Getting the parsed data as a List construct 
       list = placeJsonParser.parse(jObject); 
       break; 
      case PLACES_DETAILS: 
       PlaceDetailsJSONParser placeDetailsJsonParser = new PlaceDetailsJSONParser(); 
       // Getting the parsed data as a List construct 
       list = placeDetailsJsonParser.parse(jObject); 
     } 

    } catch (Exception e) { 
     Log.d("Exception", e.toString()); 
    } 
    return list; 
} 

@Override 
protected void onPostExecute(List<HashMap<String, String>> result) { 

    switch (parserType) { 
     case PLACES: 
      String[] from = new String[]{"description"}; 
      int[] to = new int[]{R.id.place_name}; 

      // Creating a SimpleAdapter for the AutoCompleteTextView 
      //SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), result, android.R.layout.simple_list_item_1, from, to); 

      // Setting the adapter 
      //atvPlaces.setAdapter(adapter); 

      ListAdapter adapter = new SimpleAdapter(MainActivity.this, result,R.layout.row,from,to); 
      // Adding data into listview 
      lv.setAdapter(adapter); 
      break; 
     case PLACES_DETAILS: 
      String location = atvPlaces.getText().toString(); 
      if (location != null && !location.equals("")) { 
       new GeocoderTask().execute(location); 


      } 

      break; 
    } 
} 
} 

private class GeocoderTask extends AsyncTask<String, Void, List<Address>> { 

@Override 
protected List<Address> doInBackground(String... locationName) { 
    // TODO Auto-generated method stub 

    Geocoder geocoder = new Geocoder(getBaseContext()); 
    List<Address> addresses = null; 

    try { 
     // Getting a maximum of 3 Address that matches the input text 
     addresses = geocoder.getFromLocationName(locationName[0], 3); 
    } catch (IOException e) { 
     e.printStackTrace(); 
    } 
    return addresses; 
} 

protected void onPostExecute(List<Address> addresses) { 
    if(addresses==null || addresses.size()==0){ 
     Toast.makeText(getBaseContext(), "No Location found", Toast.LENGTH_SHORT).show(); 
    } 
    for(int i=0;i<addresses.size();i++){ 
     Address address = (Address)addresses.get(i); 
     latLng = new LatLng(address.getLatitude(), address.getLongitude()); 
     String addressText = String.format("%s, %s", 
       address.getMaxAddressLineIndex() > 0 ? address.getAddressLine(0) : "", 
       address.getCountryName()); 
     MarkerOptions markerOptions = new MarkerOptions(); 
     markerOptions.position(latLng); 
     markerOptions.title("Find Location"); 
     markerOptions.icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED)); 
     FindMarker = mMap.addMarker(markerOptions); 

     CameraPosition cameraPosition = new CameraPosition.Builder().target(latLng).zoom(13).build(); 
     mMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition)); 

     loadNearByPlaces(address.getLatitude(), address.getLongitude()); 


    } 

} 

} 

} 

謝謝...

Answer 1

在

protected void onPostExecute(List<Address> addresses) { 
     if(addresses==null || addresses.size()==0){ 
    Toast.makeText(getBaseContext(), "No Location found", Toast.LENGTH_SHORT).show(); 
return; // ADD RETURN HERE 
// Your code will go beyond toast and NPE 
} 
... 

Answer 2

可能是谷歌地圖的API搜索返回null，這就是爲什麼你得到空例外，所以只檢查API鍵和谷歌地圖的權限和嘗試。 否則附上您的錯誤logcat的屏幕截圖，以獲得更多便利。

Answer 3

protected void onPostExecute(List<Address> addresses) { 
    if(addresses==null || addresses.size()==0){ 
     Toast.makeText(getBaseContext(), "No Location found", Toast.LENGTH_SHORT).show(); 
    } 
    (...) 
} 

在這裏的if語句（線845）添加

return; 

，使其：

if(addresses==null || addresses.size()==0){ 
    Toast.makeText(getBaseContext(), "No Location found", Toast.LENGTH_SHORT).show(); 
    return; 
} 

或

if(addresses==null || addresses.size()==0){ 
    Toast.makeText(getBaseContext(), "No Location found", Toast.LENGTH_SHORT).show(); 
} else for(...) {...} 

有NullPointerException異常是因爲拋出一旦你已檢查地址是否爲空y OU不破的過程，即使其爲null，則進一步呈上行

for(int i=0;i<addresses.size();i++) 

其中addresses.size（）（或null.method（））被拋出異常

Answer 4

從登錄，問題就在這裏：

try { 
    // Getting a maximum of 3 Address that matches the input text 
    addresses = geocoder.getFromLocationName(locationName[0], 3); 
} catch (IOException e) { 
    e.printStackTrace(); 
} 

爲addresses等於null，因此您必須檢查012xx方法中由IOException異常捕獲的異常，並瞭解爲什麼它不能執行getFromLocationName()方法。

然後，在你onPostExecute()方法一定要檢查是否addresses爲空或不通過它，以便循環，以確保它不會造成您的應用程序崩潰，並且可能發生這種情況通過在從if-condition返回前方法的開始：

if(addresses==null || addresses.size()==0){ 
    Toast.makeText(getBaseContext(), "No Location found", Toast.LENGTH_SHORT).show(); 
    return; 
}