我一直在尝试创建一个天气应用，该应用通过使用api调用来提供当前位置的天气。我对编码还比较陌生，我无法找出代码中出现的问题是空指针错误不断弹出。该错误发生在getTemperature（）上这是weatherData模型的代码：
package com.londonappbrewery.climapm;
public class WeatherController extends AppCompatActivity {
// Constants:
final String WEATHER_URL = "http://api.openweathermap.org/data/2.5/weather";
// App ID to use OpenWeather data
final String APP_ID = "XXXXXXXXXXXXXXXXXXX";
// Time between location updates (5000 milliseconds or 5 seconds)
final long MIN_TIME = 5000;
// Distance between location updates (1000m or 1km)
final float MIN_DISTANCE = 1000;
final int REQUEST_CODE = 123;
String LOCATION_PROVIDER = LocationManager.GPS_PROVIDER;
// Member Variables:
TextView mCityLabel;
ImageView mWeatherImage;
TextView mTemperatureLabel;
LocationManager mLocationManager;
LocationListener mLocationListener;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.weather_controller_layout);
// Linking the elements in the layout to Java code
mCityLabel = (TextView) findViewById(R.id.locationTV);
mWeatherImage = (ImageView) findViewById(R.id.weatherSymbolIV);
mTemperatureLabel = (TextView) findViewById(R.id.tempTV);
ImageButton changeCityButton = (ImageButton) findViewById(R.id.changeCityButton);
// TODO: Add an OnClickListener to the changeCityButton here:
}
// TODO: Add onResume() here:
@Override
protected void onResume() {
super.onResume();
Log.d("Clima", "onResume() called");
Log.d("Clima", "Getting weather for location");
getWeatherForCurrentLocation();
}
// TODO: Add getWeatherFor`enter code here`NewCity(String city) here:`enter code here`
// TODO: Add getWeatherForCurrentLocation() here:
private void getWeatherForCurrentLocation() {
Log.d("Clima", "onLocationChanged() callback received");
mLocationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
mLocationListener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
Log.d("Clima","onLocationChanged Called");
String longtitude = String.valueOf(location.getLongitude());
String latitude = String.valueOf(location.getLatitude());
Log.d("Clima", "The long is "+ longtitude);
Log.d("Clima", "The latitude is "+ latitude);
RequestParams params = new RequestParams();
params.put("lat",latitude);
params.put("lon",longtitude);
params.put("appid",APP_ID);
letsDoSomeNetworking(params);
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
Log.d("Clima", "onProviderDisabled");
}
};
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED &&
ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(this,new String[]{Manifest.permission.ACCESS_FINE_LOCATION},REQUEST_CODE);
return;
}
mLocationManager.requestLocationUpdates(LOCATION_PROVIDER, MIN_TIME, MIN_DISTANCE, mLocationListener);
}
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
if(requestCode==REQUEST_CODE){
if(grantResults.length>0 && grantResults[0]==PackageManager.PERMISSION_GRANTED){
Log.d("Clima","Permission granted");
getWeatherForCurrentLocation();
}else {
Log.d("Clima","Permission denied");
}
}
}
private void letsDoSomeNetworking(RequestParams params){
AsyncHttpClient client = new AsyncHttpClient();
client.get(WEATHER_URL,params,new JsonHttpResponseHandler(){
@Override
public void onSuccess(int statusCode, Header[] headers, JSONObject response){
Log.d("Clima","Success! JSON: "+response.toString());
WeatherDataModel weatherData = WeatherDataModel.fromJson(response);
updateUI(weatherData);
}
@Override
public void onFailure(int statusCode, Header[] headers,Throwable e, JSONObject response){
Log.e("Clima","Fail"+e.toString());
Log.d("Clima","Status code"+statusCode);
Toast.makeText(WeatherController.this,"Req failed",Toast.LENGTH_SHORT);
}
});
}
// TODO: Add updateUI() here:
private void updateUI(WeatherDataModel weather){
mTemperatureLabel.setText(weather.getTemperature());
mCityLabel.setText(weather.getCity());
int resID = getResources().getIdentifier(weather.getIconName(),"drawable",getPackageName());
mWeatherImage.setImageResource(resID);
}
}
这是数据模型代码：
package com.londonappbrewery.climapm;
import org.json.JSONException;
import org.json.JSONObject;
public class WeatherDataModel {
// TODO: Declare the member variables here
private String mTemperature;
private int mCondition;
private String mCity;
private String mIconName;
// TODO: Create a WeatherDataModel from a JSON:
public static WeatherDataModel fromJson(JSONObject jsonObject){
try {
WeatherDataModel weatherData = new WeatherDataModel();
weatherData.mCity = jsonObject.getString("name");
weatherData.mCondition=jsonObject.getJSONArray("weather").getJSONObject(0).getInt("Id");
weatherData.mIconName =updateWeatherIcon(weatherData.mCondition);
double tempResult = jsonObject.getJSONObject("main").getDouble("temp")-273.15;
int roundedValue = (int) Math.rint(tempResult);
weatherData.mTemperature = Integer.toString(roundedValue);
return weatherData;
}catch (JSONException e){
e.printStackTrace();
return null;
}
}
// TODO: Uncomment to this to get the weather image name from the condition:
private static String updateWeatherIcon(int condition) {
if (condition >= 0 && condition < 300) {
return "tstorm1";
} else if (condition >= 300 && condition < 500) {
return "light_rain";
} else if (condition >= 500 && condition < 600) {
return "shower3";
} else if (condition >= 600 && condition <= 700) {
return "snow4";
} else if (condition >= 701 && condition <= 771) {
return "fog";
} else if (condition >= 772 && condition < 800) {
return "tstorm3";
} else if (condition == 800) {
return "sunny";
} else if (condition >= 801 && condition <= 804) {
return "cloudy2";
} else if (condition >= 900 && condition <= 902) {
return "tstorm3";
} else if (condition == 903) {
return "snow5";
} else if (condition == 904) {
return "sunny";
} else if (condition >= 905 && condition <= 1000) {
return "tstorm3";
}
return "dunno";
}
// TODO: Create getter methods for temperature, city, and icon name:
public String getTemperature() {
return mTemperature;
}
public String getCity() {
return mCity;
}
public String getIconName() {
return mIconName;
}
}
您通过json文件初始化对象。
WeatherDataModel weatherData = WeatherDataModel.fromJson(response);
也许您的json没有关于温度的数据，响应的内容是什么。