Question

我正在尝试做什么：

Item(String name, int price, int owned){
    this.name = name;
    this.price = price;
    this.owned = owned;
}

商店活动：

public class ShopActivity extends AppCompatActivity {
    private ArrayList<AbstractItem> items = new ArrayList<AbstractItem>();
    private Game game;
    private BuySell buySell;

    Item item1 = new Item("Item1", 10, 0);
    Item item2 = new Item("Item2", 5, 0);
    Item item3 = new Item("Item3", 7, 0);

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

        game = (Game) SingletonManager.getInstance().getClassReference(Game.class);

        items.add(item1);
        items.add(item2);
        items.add(item3);

        ListView listView = (ListView) findViewById(R.id.shopList);
        final ItemsAdapter adapter = new ItemsAdapter (this, items);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new android.widget.AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                AbstractItem selectedItem = items.get(position);
                buySell.buy(selectedItem, game);
                adapter.notifyDataSetChanged();

            }
        });
    }
}

现在我的问题。每次我进入ShopActivity，它都会创建新的Object。我可以购买，比如说30个Item1，回到菜单再去购物，我得到0拥有的对象。我该怎么办这些对象只有一个？如果有人理解并可以提供帮助，非常感谢;）

Answer 1

有很多选择：

您可以创建静态对象：有其自身的缺点。
将您购买的商品放入共享偏好设置并重新创建购物车在onResume活动方法中。
将购物车存放在本地数据库中。

Answer 2

add dependency
compile 'com.google.code.gson:gson:2.6.2'

然后使用它来保存和检索项目。

public class Temp {

    private class Item {
        public Item(String name, int price, int owned) {

        }
    }

    private class ItemHolder {
        private ArrayList<Item> items;

        public ItemHolder(ArrayList<Item> items) {
            this.items = items;
        }

        public ArrayList<Item> getItems() {
            return items;
        }
    }

    public void yourMethod() {
        Context c = null;
        Item myItem1 = new Item("name", 0, 1);
        Item myItem2 = new Item("name", 0, 1);
        Item myItem3 = new Item("name", 0, 1);

        ArrayList<Item> items = new ArrayList<>();
        items.add(myItem1);
        items.add(myItem2);
        items.add(myItem3);

        //save your items
        savePersistent(new ItemHolder(items), c);

        //retrieve them anywhere
        ItemHolder savedItems = getPersistentData(c);

    }

    private void savePersistent(ItemHolder holder, Context ctx) {
        Gson gson = new Gson();
        String jsonString = gson.toJson(holder);
        SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(ctx);
        SharedPreferences.Editor editor = pref.edit();
        editor.putString("key", jsonString);
        editor.commit();
    }

    private ItemHolder getPersistentData(Context ctx) {
        SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(ctx);
        String jsonString = pref.getString("key", null);
        Gson gson = new Gson();
        ItemHolder obj = gson.fromJson(jsonString, ItemHolder.class);
        return obj;
    }

}

如何只创建一次对象并在代码中使用它？

2 个答案: