How to store an ArrayList in SharedPreferences?

Question

I have a sorted ArrayList of contacts. I want to store the list in SharedPreference. I have tried the below code:

SharedPreferences.Editor editor = app_preference.edit();
Set<String> set = new HashSet<String>();
set.addAll(contact_names_list);
editor.putStringSet("CONTACT_LIST", set);
editor.apply();

The problem is, when I retrieve this from HashSet I got an unsorted list. Is there any other way to store ArrayList other than Hashset?

Answer 1

Retrieve the values

Set<String> set = myScores.getStringSet("CONTACT_LIST", null);

Answer 2

static Prefs singleton = null;

public static Prefs with(Context context) {
        if (singleton == null) {
            singleton = new Builder(context).build();
        }
        return singleton;
    }

Do it this way-:

SharedPreferences.Editor editor = app_preference.edit();
        Set<String> set = new HashSet<String>();
        set.addAll(contact_names_list);
        editor.putStringSet("CONTACT_LIST", set);
        editor.apply();

or

Prefs.with(getAppContext()).putStringSet("CONTACT_LIST", set);

Retrive the values by using this code-:

Set<String> existindData = Prefs.with(getAppContext()).getStringSet("CONTACT_LIST", null);

Answer 3

Since putStringSet accepts any class which implements the Set interface you can use a LinkedHashSet which retains the order of insertion.

Documentaion of LinkedHashSet:

This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order).

HashSet does not retain order of insertion, which is the problem here.

// ...

Set<String> set = new LinkedHashSet<String>();

// insert from ArrayList
set.addAll(contact_names_list);

// or single elements
set.add("Homer");
set.add("Marge");

editor.putStringSet("CONTACT_LIST", set);

Answer 4

Save array in SharedPreferences :

 SharedPreferences shdPre=getSharedPreferences("MainActivity",MODE_PRIVATE);
    shdPre.edit().putInt("Size",myarray.size());
    while(i<myarray.size())
    {
shdPre.edit().remove("value"+i).commit();
shdPre.edit().putString("value"+i,myarray.get(i)).commit();
i++;
}

---

Load array from SharedPreferences

SharedPreferences shdPre=getSharedPreferences("MainActivity",MODE_PRIVATE);
 myarray =new ArrayList();
 Int msize=shdPre.getInt("Size",null);
 while(i<msize)
{
myarray.add(shdPre.getString("value" + i, null);
i++;
}

Answer 5

As the Android documentation explains https://developer.android.com/training/data-storage/shared-preferences.html?hl=en the Share Preferences is a way to save Key-Value data. Given that that behind scenes that dictionary can be save in almost a random order you can't retrieve something in order. However I can recommend a couple of solutions:

1. The easy not good performance one: Add as part of the value the index, therefore you can create an array with the size of the Hashset and then iterate the Hashset and add every element in the array that you created. O(N) temporal complexity plus the one involved in the reading process of the file.

2. Saved the data in a local SQLite database: This solution is more flexible in future terms (you can add new contacts). https://developer.android.com/training/data-storage/sqlite.html Usually you create your own SQLite database that you put in assets and then you just import it. You can create queries to bring them in the order that you want (maybe create a column for that).

   InputStream myInput = context.getAssets( ).open( "test.db" );
   
   // Path to the just created empty db
   String outFileName = "/data/YOUR_APP/test.db";
   
   // Open the empty db as the output stream
   OutputStream myOutput = new FileOutputStream( outFileName );
   
   // transfer bytes from the inputfile to the outputfile
   byte[] buffer = new byte[1024];
   int length;
   while( ( length = myInput.read( buffer ) ) > 0 )
   {
       myOutput.write( buffer, 0, length );
   }
   // Close the streams
   myOutput.flush( );
   myOutput.close( );
   myInput.close( );
   

3. Simple not scalable option: In the values folder you can always create a strings.xml file where you can put that data as a string-array. https://developer.android.com/guide/topics/resources/string-resource.html?hl=en

   <string-array name="types"> <item>A</item> <item>B and users</item> <item>C</item> <item>D</item> <item>E</item> </string-array>

If you need something more structured I have done stuff like this (saved as JSON).

<string-array name="quality_attributes">
        <item>{id:1,name:Performance,sub:[{id:2,name:Scalability},{id:3,name:Response_Time}]}</item>
        <item>{id:4,name:Security,sub:[{id:5,name:Availability,sub:[{id:6,name:Reliability},{id:7,name:Recovery}]},{id:8,name:Privacy}]}</item>
        <item>{id:9,name:Interoperability}</item>
        <item>{id:10,name:Maintainability}</item>
        <item>{id:12,name:Testability}</item>
        <item>{id:13,name:Usability,sub:[{id:14,name:Findability},{id:15,name:Correctness}]}</item>
    </string-array>

And in my code:

String[] elementsArray = getResources().getStringArray(
                R.array.quality_attributes);

        for (int i = 0; i < attributesArray.length; i++) {
            Gson gson = new Gson();
            MyJsonObject obj = gson.fromJson(elementsArray[i],
                    MyJsonObject.class);
           // Do something
        }

In general terms if you want something that needs to be change, the second options is the best one. If you are looking for something simple, the third option is good enough.

Answer 6

We can use Java 8 sorting way for sorting the collections . Set<String> s = new HashSet<String>(); s.add("Kunal"); s.add("Bhism"); s.add("Work"); s.add("Abdgg"); s.add("Psss"); s.add("Work"); List<Object> l = s.stream().sorted().collect(Collectors.toList()); System.out.println(l); Try this above code , you will get the sorted HashSet now.