CODEWITHSUNDEEP
androidlistview
bee
bee

Reputation: 1623

Saving items in listview when added from another activity

I have a listview of items in my ShoppingListActivity.

Items are added from another activity thought an intent. I want to make sure that all items are kept in the list when going between both activities; however, right now my list only has the last item added from the previous activity.

My ShoppingListActivity.class

public class ShoppingListActivity extends Activity {

    private ListView mainListView ;
    private ArrayAdapter<String> listAdapter ;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_shopping_list);

        // Find the ListView resource.
        mainListView = (ListView) findViewById( R.id.mainListView );
        ArrayList<String> shoppingList = new ArrayList<String>();
        shoppingList.add(itemLookup());

        // Create ArrayAdapter using the shopping list.
        listAdapter = new ArrayAdapter<String>(this, R.layout.simplerow, shoppingList);

        // Set the ArrayAdapter as the ListView's adapter.
        mainListView.setAdapter( listAdapter );
    }

    //Lookup item by ID
    public String itemLookup() {
        String itemName = "";
        Intent intent = getIntent();
        Bundle extras = intent.getExtras();
        if (intent != null) {
            String itemId = extras.getString("BARCODE_ID");
            try {
                itemName = ItemLookup.lookupById(itemId);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return itemName;
    }

    @Override
    public void onBackPressed() {
        startActivity(new Intent(ShoppingListActivity.this, MainActivity.class));
    }
}

I have a feeling I should be putting my add somewhere else. I'm pretty sure I should be passing the list back and forth in a putExtra, but if that's how I have to do it, it's fine.

How can I make sure that the list is maintained between activities?

Upvotes: 0

Views: 45

Answers (2)

Andrej Jurkin
Andrej Jurkin

Reputation: 2266

One way around your problem is Singleton Pattern.

In your case you can implement something like this:

public class ShoppingListManager {

    private static ShoppingListManager instance = new ShoppingListManager();

    private List<String> shoppingList;

    public static ShoppingListManager getInstance() {
        return instance;
    }

    public List<String> getShoppingList() {
        return shoppingList;
    }

    // Make the constructor private so that this class cannot be instantiated
    private ShoppingListManager(){
        shoppingList = new ArrayList<String>();
    }
}

Then access it anywhere in your code.

ShoppingListManager.getInstance().getShoppingList();

One point to remember never store context in singleton classes as it will lead to memory leaks.

Upvotes: 1

Karakuri
Karakuri

Reputation: 38605

Keeping your data structures in an Activity makes your app prone to data loss because Activities can be destroyed at various times and for a variety of reasons, including rotating the device between portrait and landscape.

You should use a separate class to store and track which items are in the shopping list. The Activity with the ListView should only get the list of items stored and display them. Anything that causes an item to be added should simply trigger a reload of the list (if the Activity is running in the foreground), otherwise the Activity should see that new item anyway the next time it starts.

If you also need your data to be persistent after your process is terminated, you should look into the possible data storage options available.

Upvotes: 1

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