android SharedPreferences 和 Map

Question

In my app I save some user information (ie name, weight, height) as key-value-pairs using SharedPreferences.

These information are used in several activities. So I thought, instead of implementing the whole procedure for reading/writing to the SharedPreferences in each activity, I also could implement a class "UserData" and define several static methods. So when I need some user information or want to save them I only use methods of the class "UserData" and this class handles all the stuff in background.

So I did the following things:

• class UserData contains a private Map<String,?>
• this map is filled by the getAll() -Method of SharedPreferences
• initialization is triggerd in the onCreate() -Method in each activity
• providing the values (for each possible type) to a defined key is done by the getValue(String key) -Method
• writing (new) information should be done by setter methods
• to write back to shared preferences, there is a save function

But now I have a lot of questions:

1. getAll() method I expect, that getAll() will read all key-value-pairs from the SharedPreferences. So I would expect, that after initialization data will contain (String,String)-pairs (ie "name";"Max") as well as (String,Integer)-pairs (ie "weight",85). Am I right?

2. getting the values Is the way, how I return the values in getValue(String key) correct? How can I get the value type from such a Map<String,?> or Map.Entry<String,?> definition?

3. adding Entries to the map I have no idea how to overwrite or write new entries to data . One Idea was, to create a set-method for each type (ie String, Integer) I can save in SharedPreferences, create an Entry within this method and then calling an add-method. But how should this looks like?

4. saving Will this saving fuction work properly? I'm not realy sure.

Or is this a total stupid approach? Thanks for your support.

This is my UserData-class

public class UserData {

    static private boolean isInit = false;

    static private Map<String,?> data = new HashMap<>();

    static void initialize(Context context){
        if(UserData.isInit){
            return;
        }
        if(context==null){
            return;
        }

        // read data from memory
        SharedPreferences pref = context.getSharedPreferences(context.getString(R.string.app_userdata),Context.MODE_PRIVATE);
        UserData.data = pref.getAll();
        Log.v(TAG,"loaded " + UserData.data.size() +" key-value-pairs into map");
        UserData.isInit=true;
    }

    static void reinitialize(Context context){
        UserData.isInit=false;
        UserData.initialize(context);
    }

    static <T> T getValue(String key){
        Object value = UserData.data.get(key);
        if(value instanceof T){
            return (T)value;
        }else{
            return null;
        }
    }

    static <T> T getValue(String key,T retErr){
        T value = getValue(key);
        if(value!=null){
            return value;
        }else{
            return retErr;
        }
    }

    static void setString(String key, String str){

    }

    static void setInteger(String key, Integer i){

    }

    static private void addElement(Map.Entry<String,?> element){
    }

    static void save(Context context){
        SharedPreferences pref = context.getSharedPreferences(context.getString(R.string.app_userdata),Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = pref.edit();

       for(Map.Entry<String,?> pair : UserData.data.entrySet()){
           Object value = pair.getValue();
           if(value instanceof String){
               editor.putString(pair.getKey(),value.toString());
           }else if(value instanceof Integer){
               editor.putInt(pair.getKey(),(Integer)value);
           }else if(value instanceof Float){
               editor.putFloat(pair.getKey(),(Float) value);
           }else if(value instanceof Boolean){
               editor.putBoolean(pair.getKey(),(Boolean) value);
           }
       }
        editor.apply();
    }
}

Sample Activity

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        UserData.initialize(getApplicationContext());
    }
}

Answer 1

i think you are trying to recreate the wheel. if you want to create a custom class for saving, adding, or even editing shared pref, that fine. Shared pref is a map, for you to use another map, just seems backwards to me.

SharedPreferences pref = getApplicationContext().getSharedPreferences("sharedPreferences", 0); // 0 - for private mode

Storing data into Shared pref.

Editor editor = pref.edit();
editor.putBoolean("name", "bill");
editor.commit();

To get the name

String name = pref.getString("name", null); //value is null if the key 'name' doesnt exist. you can also put in any string value here

remove data from shared pref

editor.remove("name");
editor.commit();

to remove everything..

editor.clear();
editor.commit();

If you want to create a class that does this, thats fine, but dont add the data into a map.