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現在Androidスタジオアプリを開発中です。 ユーザーの都市の天気を表示するためのダイアログを開くボタンを追加しました。今、私はこれをするのに苦労しています。例えば、このようなエラーが現れました。私はこの質問が既に回答されていることを知っていますが、私はまだ問題がたくさんあります。ヌルオブジェクト参照で仮想メソッド 'int java.lang.String.length（）'を呼び出そうとしています。どうすれば解決できますか？
のjava.lang.NullPointerException：nullのオブジェクト参照上の仮想メソッドを呼び出すための試み「int型java.lang.String.length（）」
これとは別に、私はそれを作るために何かを行う必要があります作業？
これは私が持っているコードです：
パブリッククラスMapsActivityはFragmentActivityは、あなたがそれ
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.naluapp.naluapp">
<!--
The ACCESS_COARSE/FINE_LOCATION permissions are not required to use
Google Maps Android API v2, but you must specify either coarse or fine
location permissions for the 'MyLocation' functionality.
-->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.CONTROL_LOCATION_UPDATES" />
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme"
android:fullBackupContent="true">
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!--
The API key for Google Maps-based APIs is defined as a string resource.
(See the file "res/values/google_maps_api.xml").
Note that the API key is linked to the encryption key used to sign the APK.
You need a different API key for each encryption key, including the release key that is used to
sign the APK for publishing.
You can define the keys for the debug and release targets in src/debug/ and src/release/.
-->
<meta-data
android:name="com.google.android.geo.API_KEY"
android:value="@string/google_maps_key" />
<activity
android:name=".MapsActivity"
android:label="@string/title_activity_maps">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
></activity>
</application>
</manifest>
必要がある場合OnMapReadyCallback、LocationListener {
private GoogleMap mMap;
LocationManager locationManager;
String provider;
LatLng myPosition;
TextView climaText;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
climaText = (TextView) findViewById(R.id.climaText);
locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
provider = locationManager.getBestProvider(new Criteria(), false);
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
return;
}
locationManager.requestLocationUpdates(provider, 400, 1, this);
/* locationRequest = new LocationRequest();
//locationRequest.setInterval(7500);
//locationRequest.setFastestInterval(5000);
locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);*/
// Obtain the SupportMapFragment and get notified when the map is ready to be used.
SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager()
.findFragmentById(R.id.map);
mapFragment.getMapAsync(this);
}
/**
* Manipulates the map once available.
* This callback is triggered when the map is ready to be used.
* This is where we can add markers or lines, add listeners or move the camera. In this case,
* we just add a marker near Sydney, Australia.
* If Google Play services is not installed on the device, the user will be prompted to install
* it inside the SupportMapFragment. This method will only be triggered once the user has
* installed Google Play services and returned to the app.
*/
@Override
public void onMapReady(GoogleMap googleMap) {
mMap = googleMap;
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
return;
}
mMap.setMyLocationEnabled(true);
Location locationActual = locationManager.getLastKnownLocation(provider);;
if(locationActual != null) {
// Getting latitude of the current location
double latitude = locationActual.getLatitude();
// Getting longitude of the current location
double longitude = locationActual.getLongitude();
// Creating a LatLng object for the current location
myPosition = new LatLng(latitude, longitude);
mMap.moveCamera(CameraUpdateFactory.newLatLng(myPosition));
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(myPosition, 16));
}
}
@Override
public void onLocationChanged(Location location) {
Log.i("TESTTAG", "onLocationChanged called");
LatLng currentPosition = new LatLng(location.getLatitude(),location.getLongitude());
mMap.moveCamera(CameraUpdateFactory.newLatLng(currentPosition));
mMap.animateCamera(CameraUpdateFactory.newLatLngZoom(currentPosition, 16));
}
@Override
public void onStatusChanged(String s, int i, Bundle bundle) {
}
@Override
public void onProviderEnabled(String s) {
}
@Override
public void onProviderDisabled(String s) {
}
@Override
protected void onResume() {
super.onResume();
if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this, Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
return;
}
locationManager.requestLocationUpdates(provider, 400, 1, this);
}
@Override
protected void onPause() {
super.onPause();
locationManager.removeUpdates(this);
}
private class CityAsyncTask extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... urls) {
String result = "";
URL url;
HttpURLConnection urlConnection = null;
try {
url = new URL(urls[0]);
urlConnection = (HttpURLConnection) url.openConnection();
InputStream in = urlConnection.getInputStream();
InputStreamReader reader = new InputStreamReader(in);
int data = reader.read();
while (data != -1){
char current = (char) data;
result += current;
data = reader.read();
}
return result;
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
try {
String mensaje = "";
JSONObject jsonObject = new JSONObject(result);
String wetherInfo = jsonObject.getString("wether");
JSONArray arr = new JSONArray(wetherInfo);
for (int i = 0; i < arr.length(); i++) {
JSONObject jsonPart = arr.getJSONObject(i);
String main = jsonObject.getString("main");
String description = jsonObject.getString("description");
if (main != "" && description != "") {
mensaje += main + " " + description + "\n\r";
}
}
if(mensaje != ""){
climaText.setText(mensaje);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}
public void obtenerClima(){
CityAsyncTask task = new CityAsyncTask();
task.execute("http://api.openweathermap.org/data/2.5/weather?q=London,uk");
}
public void startDialogReporte(View view) {
AlertDialog.Builder mBuilder = new AlertDialog.Builder(MapsActivity.this);
View mView = getLayoutInflater().inflate(R.layout.dialog_reporte,null);
mBuilder.setView(mView);
AlertDialog dialog = mBuilder.create();
dialog.show();
}
public void starDialogClima(View view){
AlertDialog.Builder mBuilder = new AlertDialog.Builder(MapsActivity.this);
View mView = getLayoutInflater().inflate(dialog_clima,null);
obtenerClima();
mBuilder.setView(mView);
AlertDialog dialog = mBuilder.create();
dialog.show();
}
}
マニフェストを実装して拡張そして天気のための私のダイアログには、テキストビュー。 JSONの結果では、 "天気" は、このような配列である
をループ可能な複製[NullPointerExceptionとは何ですか？どうすれば修正できますか？]（https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it） –