Updating data of element in a listView - android-studio

Question

I'm trying to create an app for ordering cakes and bakes.
Therefore I have a list of deserts and a list of bakes in 2 different activities.
At the moment, once you click on a dish, its quantity will raise in 1.
However, if I'm returning to the main Activity, and then again to the desert activity (or bake) then the quantity will initialize to 0, as I initialized each dish.
How can I change the dish qauntity of each view once you click on it, and it will be saved even if I leave the activity?
public class DesertsActivity extends AppCompatActivity {
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.deserts_activity);
final ArrayList<Dish> dishes = new ArrayList<Dish>();
dishes.add(new Dish("Number Cake",180, R.drawable.cake_number, 0));
dishes.add(new Dish("Ear of Haman", 40, R.drawable.ozen_haman, 0));
dishes.add(new Dish("Alphachores", 35, R.drawable.alphachores, 0));
dishes.add(new Dish("Snow Cookies", 35, R.drawable.snow_cookies, 0));
DishAdapter adapter = new DishAdapter(this, dishes);
final ListView listView = (ListView) findViewById(R.id.deserts_list);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
dishes.set(position, new Dish(dishes.get(position).getDishName(),
dishes.get(position).getDishPrice(), dishes.get(position).getDishPic(),
dishes.get(position).getQuantity()+1));
TextView quantity = (TextView) view.findViewById(R.id.quantity);
quantity.setText(String.valueOf(dishes.get(position).getQuantity()));
}
});
}
and here is the adapter
public class DishAdapter extends ArrayAdapter<Dish> {
public DishAdapter(Activity context, ArrayList<Dish> dishes){
super(context, 0, dishes);
}
#NonNull
#Override
public View getView(int position, #Nullable View convertView, #NonNull ViewGroup parent) {
View listItemView = convertView;
if(listItemView == null){
listItemView = LayoutInflater.from(getContext()).inflate(R.layout.list_layout, parent, false);
}
final Dish currenDish = getItem(position);
TextView dishName = (TextView) listItemView.findViewById(R.id.dishName);
dishName.setText(currenDish.getDishName());
TextView dishPrice = (TextView) listItemView.findViewById(R.id.dishPrice);
dishPrice.setText(String.valueOf(currenDish.getDishPrice()));
ImageView image = (ImageView) listItemView.findViewById(R.id.dishPic);
image.setImageResource(currenDish.getDishPic());
image.setVisibility(View.VISIBLE);
TextView quantity = (TextView) listItemView.findViewById(R.id.quantity);
quantity.setText(String.valueOf(currenDish.getQuantity()));
return listItemView;
}

Answer 1

Short-lived storage (system-initiated state dismissal)
To preserve and restore activity's UI state, for example due to the screen rotation, change of language while activity is running, switching into multi-window mode, or any other system-initiated state dismissal you can override onSaveInstanceState(Bundle savedInstanceState) method. Then, once activity is re-created, you can extract this state from Bundle passed to activity's onCreate method.
Saved instance state bundles persist both configuration changes and process death, but are limited by amount of storage and speed because onSavedInstanceState() serializes data to disk. Serialization can consume a lot of memory if the objects being serialized are complicated. Because this process happens on the main thread during a configuration change, serialization can cause dropped frames and visual stutter if it takes too long.
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.deserts_activity);
if(savedInstanceState != null) {
// restore your data
}
//...
}
Then input Bundle parameter is essentially a Map which takes key-value pairs. Though be aware that there are situations in which this method is not being called. See the docs for onCreate and onSaveInstanceState.
Long-lived storage
To persist a state even after application is closed, consider using databases (SQLite, Realm, etc.), file, or shared preferences.
Persistent local storage, such as a database or shared preferences, will survive for as long as your application is installed on the user’s device (unless the user clears the data for your app). While such local storage survives system-initiated activity and application process death, it can be expensive to retrieve because it will have to be read from local storage in to memory. Often this persistent local storage may already be a part of your application architecture to store all data you don’t want to lose if you open and close the activity.
See Saving UI states