只能从数组中获得行，不能存储多个行的覆盖

Question

如果Anny知道这个问题，请提前告诉我一个解决方案-- addFavorite方法只能从数组中获取行，不能存储超过一个行--它用getfavourites方法覆盖

 public class SharedPreference {

    public static final String PREFS_NAME = "PRODUCT_APP";
    public static final String FAVORITES = "Product_Favorite";

    public SharedPreference() {
        super();
    }

    // This four methods are used for maintaining favorites.
    public void saveFavorites(Context context, List<Product> favorites) {
        SharedPreferences settings;
        Editor editor;

        settings = context.getSharedPreferences(PREFS_NAME,
                Context.MODE_PRIVATE);
        editor = settings.edit();

        Gson gson = new Gson();
        String jsonFavorites = gson.toJson(favorites);

        editor.putString(FAVORITES, jsonFavorites);

        editor.commit();
    }

    public void addFavorite(Context context, Product product) {
        List<Product> favorites = getFavorites(context);
        if (favorites == null)
            favorites = new ArrayList<Product>();
        favorites.add(product);
        saveFavorites(context, favorites);
    }

    public void removeFavorite(Context context, Product product) {
        ArrayList<Product> favorites = getFavorites(context);
        if (favorites != null) {
            favorites.remove(product);
            saveFavorites(context, favorites);
        }
    }

    public ArrayList<Product> getFavorites(Context context) {
        SharedPreferences settings;
        List<Product> favorites;

        settings = context.getSharedPreferences(PREFS_NAME,
                Context.MODE_PRIVATE);

        if (settings.contains(FAVORITES)) {
            String jsonFavorites = settings.getString(FAVORITES, null);
            Gson gson = new Gson();
            Product[] favoriteItems = gson.fromJson(jsonFavorites,
                    Product[].class);

            favorites = Arrays.asList(favoriteItems);
            favorites = new ArrayList<Product>(favorites);
        } else
            return null;

        return (ArrayList<Product>) favorites;
    }
}

Answer 1

每次在add方法中，您都使用了新关键字，这意味着您正在用新列表覆盖之前的列表。首先需要从存储的共享Prefrence中添加getList，然后将新项添加到该列表中。

public void addFavorite(Context context, Product product) {
    List<Product> favorites = new ArrayList<Product>();


    // this line cause you problem.
    //   favorites = new ArrayList<Product>();
    // this line cause you problem.

    // add code from below line

    favorites=getFavorites(context);
    if(favorites!=null)
    {
        favorites.add(product);
    }

    saveFavorites(context, favorites);
}