用上一个活动中的项目填充ListView

Question

I'm new to Android programming, and still teaching myself to code.

Currently I'm teaching myself about GridViews and still coding that project with tutorials so I have nothing to show right now, but the basic idea is the following...

If I have images of groceries in GridView in the first activity and when you click an image you will be able to open a new activity with a larger image and you could input the number how many you things you need, like 5 apples or whatever.

All of that is more or less clear to me how to do.

But how would I send the number and image to a new (third) activity with a ListView that would list all the items you need to buy at the grocery store? How would I be able to fill the list only with items after you enter the number on the previous activity with the large picture and click an "OK" or "Add" button or whatever and not list absolutely everything?

Thanks!

Answer 1

It's difficult at first, but you can use an SQLiteDatabase to store the data. It's not a quick solution for you, but definitely worth learning about if you're serious to learn android. Here's a link to the official stuff: https://developer.android.com/reference/android/database/sqlite/SQLiteDatabase.html

I personally used this tutorial: http://www.androidwarriors.com/2016/02/android-sqlite-database-tutorial-sqlite.html?m=1

Answer 2

Sharing some data between multiple activities or fragments is a very common situation. One way around it is implementing a Singleton Pattern .

In your case you can design some kind of data structure for your purpose and manage it inside shared singleton class. For example something like this:

public class ShoppingListManager {

    private static ShoppingListManager instance = new ShoppingListManager();

    private List<ShoppingItem> shoppingList;

    public static ShoppingListManager getInstance() {
        return instance;
    }

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

    public void addShoppingItem(ShoppingItem item) {
        this.shoppingList.add(item);
    }

    ...

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

Then you can access your data anywhere in your code and manage shared data in any way you'd like.

ShoppingListManager.getInstance().getShoppingList();

// You can add items in any activity
ShoppingListManager.getInstance().addShoppingItem(item);

One point to remember store context in singleton classes as it will lead to memory leaks.