我有一个片段需要在屏幕旋转时恢复其包含的RecyclerView。我一直在使用onViewStateRestored（）和onSaveInstantState（）的标准过程。但是，当我旋转屏幕时，我得到一个零点异常。在onCreate（）期间出现问题，如下面的代码和logcat所示。任何关于我做错的详细说明都将不胜感激。
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();
}
}
以下是logcat输出：
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
答案 0 :(得分：1)
WHERE hd IN ("%");
在mLinearLayoutManager中为空，因为您在onCreate中创建了它。在onCreateView()中创建一个实例，并在onCreate中重复使用。
答案 1 :(得分：0)
你错误地做了。您不需要保存layoutManager以进行旋转更改，只需每次都实例化它。如果您有任何其他 DATA 保存它们并使用它们来创建layoutManager。我有一个需要恢复其包含的片段 屏幕旋转时RecyclerView。我一直在使用这个标准 使用onViewStateRestored（）和onSaveInstantState（）的过程。 但是，当我旋转屏幕时，我得到一个零点异常。