如何将数组列表从活动发送到另一个活动，而不访问另一个活动

Question

I tried to get an answer for this before but couldn't get one that would solve my problem. I'm making app which keeps disc golf scores. my MainActitivity has 4 buttons. New game, resume game, courses and players.

Atm when user goes to ActivityPlayers (Players button in main activity), user can add and delete players, and shared preferences keep that list save. But now I also need to somehow get that same list of players, to that ActivityNewGame (New game button in main activity), there I need to loop through that list, and use those names to make new items in ActivityNewGame list. (cannot just copy the list from ActivityPlayers straight, because in that recyclerview, those items have different buttons than new game recyclerview has, even tho they use the same list of names.)

I tried to do intent, but I realized that I can't use that because I have to visit that ActivityNewGame when a user adds or delete players from ActivityPlayers...

This is the way I tried

This is my ActivityPlayers.java method. This method will be called when the user adds a new name to mNamelist.

private void addItem(int position) {
    /** Get user input (name) **/
    textAdd = findViewById(R.id.name_input);

    /** Add name to the list **/
    mNameList.add(position, new NameItem(textAdd.getText().toString().trim()));

    /** sort that list **/
    sortArrayList();

    /** save changes to shared preferences **/
    saveData();

    /** Show changed list to user **/
    mAdapter.notifyItemInserted(position);

    /** Clear the input field **/
    textAdd.getText().clear();

    /** Send namelist to ActivitynewGame **/
    Intent i = new Intent(ActivityPlayers.this, ActivityNewGame.class);
    i.putExtra("PlayerList", mNameList);
    startActivity(i);
}

This is my savedata() method to save changes that user makes for namelist in ActivityPlayers:

private void saveData() {
    SharedPreferences sharedPreferences = getSharedPreferences("shared preferences", MODE_PRIVATE);
    SharedPreferences.Editor editor = sharedPreferences.edit();
    Gson gson = new Gson();
    String json = gson.toJson(mNameList);
    editor.putString("task list", json);
    editor.apply();
}

This is my ActivityNewGame:

public class ActivityNewGame extends AppCompatActivity {
    private ArrayList<NewGamePlayerItem> mPlayerList;

    private RecyclerView mRecyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager mLayoutManager;

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

        mPlayerList = new ArrayList<>();
        Intent intent = getIntent();
        ArrayList<NameItem> mNameList = (ArrayList<NameItem>) intent.getSerializableExtra("PlayerList");

        /** Check if mNameList has any items in it. **/
        if (mNameList.size() != 0) {
        /** Loop through that arraylist and set its names into this Activity items. ("true" is for checkbox that this item has.) **/
            for (int i = 0; i < mNameList.size(); i++) {
                mPlayerList.add(new NewGamePlayerItem(true, mNameList.get(i).getText1()));
            }
        }

        buildRecyclerView();
    }

The problem here is that I don't want to visit ActivityNewGame, I just want to pass that name list from ActivityPlayers, and when user choose to go to make a new game (ActivityNewGame), then that player list would be there. So what should I do differently to manage to do that?

Please give me some examples of ideas if you have, thank you.

Answer 1

In ActivityPlayers.java addItem() method, save your data in shared preferences.

private void addItem(int position) {
    /** Get user input (name) **/
    textAdd = findViewById(R.id.name_input);

    /** Add name to the list **/
    mNameList.add(position, new NameItem(textAdd.getText().toString().trim()));

    /** sort that list **/
    sortArrayList();

    /** save changes to shared preferences **/
    saveData();

    /** Show changed list to user **/
    mAdapter.notifyItemInserted(position);

    /** Clear the input field **/
    textAdd.getText().clear();

    /** save data to shared pref **/
    SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);
  Editor editor = prefs.edit();
  try {
    editor.putString(<KEY_NAME>, ObjectSerializer.serialize(mNameList));
  } catch (IOException e) {
    e.printStackTrace();
  }
  editor.commit();
}

and in ActivityNewGame.java extract the ArrayList from shared preferences like so.

mNewNameList = new ArrayList<NewGamePlayerItem>();
 // load NewGamePlayerItems from preference
  SharedPreferences prefs = getSharedPreferences(SHARED_PREFS_FILE, Context.MODE_PRIVATE);

  try {
    mNewNameList = (ArrayList<NewGamePlayerItem>) ObjectSerializer.deserialize(prefs.getString(<KEY_NAME>, ObjectSerializer.serialize(new ArrayList<NewGamePlayerItem>())));
  } catch (IOException e) {
    e.printStackTrace();
  } catch (ClassNotFoundException e) {
    e.printStackTrace();
  }

Answer 2

您可以使用RxBus将数据发送到另一个活动，而无需访问它。

Answer 3

You can save your arraylist in one file.

public void save(String fileName) throws FileNotFoundException {
String tmp = clubs.toString();
PrintWriter pw = new PrintWriter(new FileOutputStream(fileName));
pw.write(tmp);
pw.close();
}

Answer 4

You can make the list static and then you don't need to pass it. You can use it inside your app anywhere you want.

By making it static there may arise memory leaks problem so dispose them correctly after using it.