SharedPreferences 会覆盖其他值吗？

Question

I am new in android.here i make simple contacts list app. when user click on contact items, contact add in favorite list. but problem is that when user click on first contact item to add favorite,then user click second contact,but first item was remove automatically. Shared Preferences overwrite other value,i want to add item in list so what i do to add contacts in favorite List.

First Fragment:

imageViewfavourite.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
                SharedPreferences.Editor editor = preferences.edit();

                editor.putString("name1", Pname);
                editor.putString("number1", Pnumber);
                editor.putString("image1", temp);
                editor.putInt("pos", position);

                Log.e("a", "name1" + Pname);
                Log.e("a", "number1" + Pnumber);
                Log.e("a", "image1" + temp);

                editor.commit();

            }
        });

Second Fragment:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

View view = inflater.inflate(R.layout.fragment_fragment_fv, container, false);
recyclerView = (RecyclerView) view.findViewById(R.id.favourite_list);
selectUsers = new ArrayList<DataContact>();

SharedPreferences preferences = getActivity().getPreferences(0);
String Pname = preferences.getString("name1", "");
String Pnumber = preferences.getString("number1", "");
String Pimage = preferences.getString("image1", "");

byte[] encodeByte = Base64.decode(Pimage, Base64.DEFAULT);
bitmap = BitmapFactory.decodeByteArray(encodeByte, 0, encodeByte.length);

Log.v("name1", Pname);
Log.v("number1", Pnumber);
Log.v("image1", Pimage);

DataContact selectUser = new DataContact();
selectUser.setName(Pname);
selectUser.setPhone(Pnumber);
selectUser.setThumb(bitmap);
selectUsers.add(selectUser);

adapter = new AdapterFv(getActivity(), "");
LinearLayoutManager llm = new LinearLayoutManager(getActivity());
llm.setOrientation(LinearLayoutManager.VERTICAL);
recyclerView.setLayoutManager(llm);
adapter.setData(selectUsers);
recyclerView.setAdapter(adapter);

return view;
}

Answer 1

Check the api documentation before asking question.

Explain

SharedPreferences is supported store data ( 1:1 key-value match ) therefore, a key can have only one data item.

Storable Types

• boolean
• float
• int
• long
• String
• Set<String>

Simple Solution

// in Second Fragment 
String Pname = preferences.getString("name2", "");
String Pnumber = preferences.getString("number2", "");
String Pimage = preferences.getString("image2", "");

Reference

https://developer.android.com/reference/android/content/SharedPreferences.html

Answer 2

in shared preference, you are putting value and editing value via KEY if you use the same key that will overwrite your value. because shared preference containing KEY VALUE pair if you want to store the data use SQLite database. Shared Preference can hold onlysingle value for each key

Answer 3

You are adding the second contact with the same keys that you used for first contact. What you need is some sort of counter that keeps track of the number of contacts you have saved and then modifies your keys accordingly.

If I am not wrong then you are using

position

as the counter. You just need to modify the keys. A good solution would be to make separate methods to write and extract contact from shared preferences.

public void writeContact(String Pname, String Pnumber, String temp,int position)
{
     SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity());
            SharedPreferences.Editor editor = preferences.edit();

            editor.putString("name"+position, Pname);
            editor.putString("number"+position, Pnumber);
            editor.putString("image"+position, temp);

            editor.commit();
}


public DataContact getContact(int position)
{
    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getActivity());

    DataContact selectUser = new DataContact();

    selectUser.setName(preferences.getString("name"+position, ""));
    selectUser.setPhone( preferences.getString("number"+position, ""));
    selectUser.setThumb(preferences.getString("image"+position, ""));

    return selectUser;
}

This should do it. Now to save your contact you need to call writeContact method in the onClick(). Similarly you can call getContact() with position as parameter to get the contacts.

Answer 4

Better way would be to use database.But if you want to use SharedPreferences to save your data you can create Serializable class User and class Preference for managing your SharedPreferences as @AmitBhati said.

    public class Preference {

    private static final String USER_JSON = "user_json";

    private SharedPreferences mSettings;
    private Context ctx;

    public Preference(Context context) {
        ctx = context;
        mSettings = PreferenceManager.getDefaultSharedPreferences(context);
    }

    public void setUsersJson(List<User> u){
        Gson gson = new Gson();
        String jsonStr = gson.toJson(u);
        SharedPreferences.Editor editor = mSettings.edit();
        editor.putString(USER_JSON, jsonStr);
        editor.apply();
    }
    public List<User> getUsersJson(){
        Gson gson = new Gson();
        String jsonStr = mSettings.getString(USER_JSON, null);
        Type listType = new TypeToken<List<HourlyWeather>>(){}.getType();
        return (List<User>) gson.fromJson(jsonStr, listType);
    }
}

Answer 5

I am using Shared preference as well and had doubt on the same topic, does it get over written. Your problem seems a bit different than mine considering the size of contact list, what i used was created a separate function in which i will be sending key value eg:key_val_, now since there will be 'n' contacts use for loop and add it with the above string.

String string=key_val_;

for(int i=0;i < n; i++){

editor.putInt(string+i, ur_value); }

Not sure if it cause memory problems in your case.

Answer 6

Generally, Shared Preferences is used for small data and also in your app not store the big data.Every key keeps one value in Shared Preferences. Possibly, you can change "name" key to "name1" if the "name" key store some data but it is not easy and hard to handle exception. You can use Sqlite and it is more easy to control data with queries.