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画面の回転時にRecyclerViewを含むフラグメントを復元する必要があるフラグメントがあります。私はonViewStateRestored（）とonSaveInstantState（）で標準のプロシージャを使用しています。しかし、私は、画面を回転させるとヌルポイントの例外が発生します。問題はonCreate（）の間に私のコードとlogcat以下のように発生します。私が間違っていることに関する詳細な指示は、大いに感謝します。以下はonRestoreInstanteState（）で回転後のRecyclerviewを復元する方法
import android.app.ProgressDialog;
import android.content.Context;
import android.os.Bundle;
import android.os.Parcelable;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Toast;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.google.gson.Gson;
import org.json.JSONObject;
import static uk.co.my_package.weatherscan.Utils.getForecastEndPoint;
public class PlaceForecastListFragment extends Fragment {
public static final String PAGERTABTITLE = "Forecast";
private static final String CITYID = "weather_cityid";
private static final String SEVENDAYS = "7";
private static final String LIST_STATE_KEY = "list_state";
private static final String TAG = PlaceForecastListFragment.class.getSimpleName();
private LinearLayoutManager mLinearLayoutManager;
private RecyclerView mRecyclerView;
private Parcelable mListState;
private ProgressDialog pDialog;
private String mCityId;
public PlaceForecastListFragment() {
// Required empty public constructor
}
public static PlaceForecastListFragment newInstance(String cityid) {
PlaceForecastListFragment fragment = new PlaceForecastListFragment();
Bundle args = new Bundle();
args.putString(CITYID, cityid);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mCityId = getArguments().getString(CITYID);
}
if (savedInstanceState == null) {
// Shows message to user while makeJsonObjectRequest() is still running.
pDialog = new ProgressDialog(getContext());
pDialog.setMessage("Getting weather forecast...");
pDialog.setCancelable(false);
// Make JSON request
makeJsonObjectRequest(mCityId);
} else {
// Problem arises here!!!!!!!!!!!!!!!!!!!!
mLinearLayoutManager.onRestoreInstanceState(mListState);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_place_forecast_list, container, false);
if (view instanceof RecyclerView) {
Context context = view.getContext();
mRecyclerView = (RecyclerView) view;
mLinearLayoutManager = new LinearLayoutManager(context);
mRecyclerView.setLayoutManager(mLinearLayoutManager);
}
return view;
}
@Override
public void onViewStateRestored(Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
if (savedInstanceState != null) {
mListState = savedInstanceState.getParcelable(LIST_STATE_KEY);
mRecyclerView.getLayoutManager().onRestoreInstanceState(mListState);
}
}
@Override
public void onSaveInstanceState(Bundle savedInstantState) {
super.onSaveInstanceState(savedInstantState);
//mListState = mLinearLayoutManager.onSaveInstanceState();
savedInstantState.putParcelable(LIST_STATE_KEY, mRecyclerView.getLayoutManager().onSaveInstanceState());
}
// TODO CBA: Move this method to its own class and call it from here. This will be more organized.
/**
* Method to make json object request
*/
private void makeJsonObjectRequest(final String cityId) {
showpDialog();
String url = getForecastEndPoint(cityId, SEVENDAYS);
JsonObjectRequest jsonObjReq = new JsonObjectRequest(Request.Method.GET,
url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
// Log response
Log.d(TAG, response.toString());
String responseString = String.valueOf(response);
Gson gson = new Gson();
ResponseForecastConditions responseForecastConditionsObj =
gson.fromJson(responseString, ResponseForecastConditions.class);
mRecyclerView.setAdapter(new ForecastAdapter(responseForecastConditionsObj,
getContext()));
// Hide dialog after information has been requested
hidepDialog();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
// Warn user
Toast.makeText(getContext(),
"No internet connection", Toast.LENGTH_LONG).show();
// hide the progress dialog
hidepDialog();
}
});
// Adding request to request queue
AppController.getInstance().addToRequestQueue(jsonObjReq);
}
/**
* Method for showing dialog
*/
private void showpDialog() {
if (!pDialog.isShowing())
pDialog.show();
}
/**
* Method for hiding dialog
*/
private void hidepDialog() {
if (pDialog.isShowing())
pDialog.dismiss();
}
}
logcat出力です：あなたはonCreateView()でそれを作成するため
03-20 16:32:40.801 6371-6405/uk.co.my_package.weatherscan E/Surface: getSlotFromBufferLocked: unknown buffer: 0xab7cfcb0
03-20 16:32:40.823 6371-6371/uk.co.my_package.weatherscan D/AndroidRuntime: Shutting down VM
03-20 16:32:40.823 6371-6371/uk.co.my_package.weatherscan E/AndroidRuntime: FATAL EXCEPTION: main
Process: uk.co.my_package.weatherscan, PID: 6371
java.lang.RuntimeException: Unable to start activity ComponentInfo{uk.co.my_package.weatherscan/uk.co.my_package.weatherscan.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.LinearLayoutManager.onRestoreInstanceState(android.os.Parcelable)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4077)
at android.app.ActivityThread.-wrap15(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1350)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.LinearLayoutManager.onRestoreInstanceState(android.os.Parcelable)' on a null object reference
at uk.co.my_package.weatherscan.PlaceForecastListFragment.onCreate(PlaceForecastListFragment.java:68)
at android.support.v4.app.Fragment.performCreate(Fragment.java:1951)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1029)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1234)
at android.support.v4.app.FragmentManagerImpl.dispatchCreate(FragmentManager.java:2041)
at android.support.v4.app.Fragment.performCreate(Fragment.java:1964)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1029)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1234)
at android.support.v4.app.FragmentManagerImpl.dispatchCreate(FragmentManager.java:2041)
at android.support.v4.app.FragmentController.dispatchCreate(FragmentController.java:163)
at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:332)
at android.support.v7.app.AppCompatActivity.onCreate(AppCompatActivity.java:74)
at uk.co.my_package.weatherscan.MainActivity.onCreate(MainActivity.java:15)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4077)
at android.app.ActivityThread.-wrap15(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1350)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
03-20 16:33:58.373 6371-6378/uk.co.my_package.weatherscan W/art: Suspending all threads took: 24.263ms
03-20 16:34:04.875 6371-6378/uk.co.my_package.weatherscan W/art: Suspending all threads took: 17.116ms
03-20 16:36:28.696 6371-6378/uk.co.my_package.weatherscan W/art: Suspending all threads took: 15.452ms
03-20 16:37:40.836 6371-6371/? I/Process: Sending signal. PID: 6371 SIG: 9
こんにちは@ greywolf82。私はあなたが正しいと思います。しかし、私は細部を見逃していると思う。 onCreateView（）に何を置くべきですか？私が何をする必要があるかを具体的に教えてください。前もって感謝します。 – CBA110
クラス属性を使用するだけです。しかし、あなたはonCreateでそれを作成する必要があります – greywolf82