Java 为什么SharedReference不在这里保存？

我试图在SharedReferences中设置一些字符串，但当我重新启动应用程序时，首选项为空，因此在getString方法中返回“null”

public class settingsView extends Fragment {

    DataSnapshot citiesSnap;
    Spinner theaterSpinner, citySpinner;
    String selectedCity, selectedTheater;
    String[] cities = {"Bagalkot", "Belgaum", "Bellary", "Bijapur", "Chitradurga", "Davanagere", "Dharwad", "Gadag", "Hassan", "Hosapete", "Hospet", "Hubli", "Mysore", "Shimoga", "Tumkur"};
    List<String>theaters ;

    public settingsView() {
        Log.d("testing" , "settingsview constructor called");
        citiesSnap = null;
        theaterSpinner = null;
        citySpinner = null;
        selectedCity = null;
        selectedTheater = null;
        theaters = null ;
    }


    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        Log.d("testing", "Called onActivityCreated");
        citySpinner = (Spinner) getActivity().findViewById(R.id.citySpinner);
        theaterSpinner = (Spinner) getActivity().findViewById(R.id.theaterSpinner);


        final SharedPreferences mSettings = this.getActivity().getPreferences(Context.MODE_PRIVATE);
        selectedCity = mSettings.getString("selectedCity", "null" );
        selectedTheater = mSettings.getString("selectedTheater", "null");

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity().getApplicationContext(), android.R.layout.simple_selectable_list_item, cities);
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        citySpinner.setAdapter(adapter);

        updateTheatersSpinner(selectedCity);

        if(theaters!=null)
            theaterSpinner.setSelection(theaters.indexOf(selectedTheater));


        FirebaseDatabase.getInstance().getReference("movies/karnataka").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                citiesSnap = dataSnapshot;
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });


        citySpinner.setOnItemSelectedListener(new Spinner.OnItemSelectedListener() {
            @Override
            public void onItemSelected(Spinner parent, View view, int position, long id) {
                updateTheatersSpinner(citySpinner.getSelectedItem().toString());
                mSettings.edit().putString("selectedCity" , citySpinner.getSelectedItem().toString()).commit();
            }
        });

        theaterSpinner.setOnItemSelectedListener(new Spinner.OnItemSelectedListener() {
            @Override
            public void onItemSelected(Spinner parent, View view, int position, long id) {
                mSettings.edit().putString("selectedTheater" , theaterSpinner.getSelectedItem().toString()).commit() ;
            }
        });
    }


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.settingsview, container, false);
        return view;
    }


    @Override
    public void onSaveInstanceState(@NonNull Bundle outState) {
        Log.d("testing" , "On save instancestate") ;
        super.onSaveInstanceState(outState);

        SharedPreferences preferences = this.getActivity().getPreferences(Context.MODE_PRIVATE);
        preferences.edit().putString("selectedCity", selectedCity).putString("selectedTheater", theaterSpinner.getSelectedItem().toString()).commit();
    }


    public void updateTheatersSpinner(String city) {

        if (citiesSnap != null) {
            ArrayList<String> theaterlist = new ArrayList<>();

            for (DataSnapshot snapshot : citiesSnap.child(city).getChildren()) {
                theaterlist.add(snapshot.getKey());
            }

            this.theaters =  theaterlist ;

            Log.d("firebasedata", "theaterlist : " + theaterlist.toString());

            ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity().getApplicationContext(), android.R.layout.simple_selectable_list_item, theaterlist);
            adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
            this.theaterSpinner.setAdapter(adapter);
        }
    }
}

公共类设置视图扩展了片段{
DataSnapshot citiesSnap；
旋转器剧院旋转器，城市旋转器；
字符串selectedCity，SelectedThewer；
字符串[]城市={“巴加尔科特”、“贝尔高姆”、“贝拉里”、“比贾普尔”、“奇特拉杜加”、“达瓦盖尔”、“达瓦德”、“加达格”、“哈桑”、“霍萨佩特”、“霍斯佩特”、“胡比”、“迈索尔”、“希莫加”、“图姆库尔”}；
剧院；
公共设置视图（）{
d（“测试”、“设置视图构造函数调用”）；
citiesSnap=null；
theaterSpinner=null；
citySpinner=null；
selectedCity=null；
SelectedThewer=null；
剧院=空；
}
@凌驾
ActivityCreated上的公共无效（@Nullable Bundle savedinStateCState）{
super.onActivityCreated（savedInstanceState）；
Log.d（“测试”，“称为onActivityCreated”）；
citySpinner=（微调器）getActivity（）.findViewById（R.id.citySpinner）；
theaterSpinner=（Spinner）getActivity（）.findViewById（R.id.theaterSpinner）；
最终SharedReferences mSettings=this.getActivity（）.getPreferences（Context.MODE\u PRIVATE）；
selectedCity=mSettings.getString（“selectedCity”、“null”）；
selectedthewer=mSettings.getString（“selectedthewer”、“null”）；
ArrayAdapter=新的ArrayAdapter（getActivity（）.getApplicationContext（），android.R.layout.simple\u可选\u列表\u项，城市）；
setDropDownViewResource（android.R.layout.simple\u微调器\u下拉菜单\u项）；
citySpinner.setAdapter（适配器）；
更新aterspinner（selectedCity）；
如果（剧院！=null）
剧院微调器.setSelection（剧院.indexOf（SelectedThewer））；
FirebaseDatabase.getInstance（）.getReference（“电影/卡纳塔克邦”）.addValueEventListener（新的ValueEventListener（））{
@凌驾
public void onDataChange（@NonNull DataSnapshot DataSnapshot）{
citiesSnap=dataSnapshot；
}
@凌驾
已取消的公共void（@NonNull DatabaseError DatabaseError）{
}
});
citySpinner.setOnItemSelectedListener（新微调器.OnItemSelectedListener（）{
@凌驾
已选择公共空间（微调器父对象、视图、整型位置、长id）{
更新aterspinner（citySpinner.getSelectedItem（）.toString（））；
mSettings.edit（）.putString（“selectedCity”，citySpinner.getSelectedItem（）.toString（））.commit（）；
}
});
theaterSpinner.setOnItemSelectedListener（新建Spinner.OnItemSelectedListener（））{
@凌驾
已选择公共空间（微调器父对象、视图、整型位置、长id）{
mSettings.edit（）.putString（“selectedthewer”，theaterSpinner.getSelectedItem（）.toString（））.commit（）；
}
});
}
@可空
@凌驾
创建视图时的公共视图（@NonNull LayoutInflater inflater、@Nullable ViewGroup container、@Nullable Bundle savedInstanceState）{
视图=充气机。充气（R.layout.Settings视图，容器，错误）；
返回视图；
}
@凌驾
SAVEInstanceState上的公共无效（@NonNull Bundle outState）{
Log.d（“测试”、“保存实例状态”）；
super.onSaveInstanceState（超出状态）；
SharedReferences preferences=this.getActivity（）.getPreferences（Context.MODE\u PRIVATE）；
preferences.edit（）.putString（“selectedCity”，selectedCity）.putString（“selectedthewer”，theaterSpinner.getSelectedItem（）.toString（））.commit（）；
}
public void updateTheaterspinner（字符串城市）{
如果（citiesSnap！=null）{
ArrayList theaterlist=新的ArrayList（）；
for（DataSnapshot快照：citiesSnap.child（city.getChildren（））{
添加（snapshot.getKey（））；
}
this.theaters=剧院列表；
Log.d（“firebasedata”，“theaterlist:+theaterlist.toString（））；
ArrayAdapter=新的ArrayAdapter（getActivity（）.getApplicationContext（），android.R.layout.simple\u可选\u列表\u项，theaterlist）；
setDropDownViewResource（android.R.layout.simple\u微调器\u下拉菜单\u项）；
this.theaterSpinner.setAdapter（适配器）；
}
}
}

您有类字段

selectedCity

和

SelectedThewer

，您从不更新它们，因此它们总是

null

，但是在

onSaveInstanceState

中保存这些字段，因此当您的活动关闭时，它会将

null

写入

共享引用中的两个字段。spnner更改时，您应该更新这些字段

    citySpinner.setOnItemSelectedListener(new Spinner.OnItemSelectedListener() {
        @Override
        public void onItemSelected(Spinner parent, View view, int position, long id) {
            selectedCity = citySpinner.getSelectedItem().toString(); // <--
            updateTheatersSpinner(selectedCity);
            mSettings.edit().putString("selectedCity", selectedCity).commit();
        }
    });

    theaterSpinner.setOnItemSelectedListener(new Spinner.OnItemSelectedListener() {
        @Override
        public void onItemSelected(Spinner parent, View view, int position, long id) {
            selectedTheater = theaterSpinner.getSelectedItem().toString(); // <--
            mSettings.edit().putString("selectedTheater", selectedTheater).commit();
        }
    });

是否尝试使用GetDefaultSharedReferences（）？保存所选城市时使用了错误的微调器（剧院）。
@Override
public void onSaveInstanceState(@NonNull Bundle outState) {
    Log.d("testing" , "On save instancestate") ;
    super.onSaveInstanceState(outState);

    SharedPreferences preferences = this.getActivity().getPreferences(Context.MODE_PRIVATE);
    preferences.edit()
        .putString("selectedCity", selectedCity)
        .putString("selectedTheater", selectedTheater)
    .commit();
}