How to get the number of elements in several Spinner View and calculate the total cost

, .

IDetails, . , , . , , .

, . , .

public abstract class ShoppingItem {

    /* You can add more fields here, for example an image */

    protected String title;
    protected String description;

    protected int cost;

    // Each object keeps track of how many of itself is being bought
    protected int numberBought = 1;

    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }

    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }

    public int getCost() {
        return cost;
    }
    public void setCost(int cost) {
        this.cost = cost;
    }

    public int getNumberBought() {
        return numberBought;
    }

    public void setNumberBought(int numberBought) {
        this.numberBought = numberBought;
    }   
}

:

public class Banana extends ShoppingItem {
    public Banana() {
        this.title = "Banana";
        this.description = "A tasty banana";
        this.cost = 100;
    }
}   

public class Apple extends ShoppingItem {
    public Apple() {
        this.title = "Apple";
        this.description = "A fresh apple";
        this.cost = 200;
    }
}

Now that we have all the models sorted, how do we type ListViewwith them most efficiently? With custom Adapter, just like you. We will fix spinner reset when scrolling, and also add some excellent performance improvements.

public class ShoppingAdapter extends ArrayAdapter<ShoppingItem> {

    // We use this LayoutInflater to inflate the xml for each row in the list
    private LayoutInflater mInflater;

    // This is the strings that will populate the spinners
    // Can be moved to res/values/string-array.xml to prevent hardcoded strings
    private String[] spinnerArray = new String[] { "No. items: 1", 
                                                   "No. items: 2",
                                                   "No. items: 3",
                                                   "No. items: 4"};

    public ShoppingAdapter(Context context, int resource, ArrayList<ShoppingItem> objects) {
        super(context, 0, objects);

        // Initialize the declared LayoutInflater 
        mInflater = LayoutInflater.from(context);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        // This is a simple reference holding class, so we don't have to call
        // findViewById() every time getView() is called. Improved performance :)
        ViewHolder holder = null;

        if(convertView == null) { 
            // If convertView is null, then we don't have a view to place
            // our data in. We have to inflate one ourself
            convertView = mInflater.inflate(R.layout.list_item, null);

            // Store a reference to the Spinner and the TextView in 
            // the ViewHolder object
            holder = new ViewHolder();          
            holder.spinner = (Spinner) convertView.findViewById(R.id.spinner);
            holder.textView = (TextView) convertView.findViewById(R.id.total);

            // Attach the ViewHolder object to convertView, as a tag
            convertView.setTag(holder);
        }
        else {
            // If convertView is non-null then we can fetch the ViewHolder object
            // we stored in the tag earlier. We now have references to both the Spinner 
            // and TextView, through the ViewHolder object.
            holder = (ViewHolder) convertView.getTag();
        }

        // If the holder is non-null, we are good to go!
        if(holder != null) {
            // Fetch the item from the underlying ArrayList
            final ShoppingItem item = getItem(position);

            // We need this to be final, so we can access it inside the 
            // onItemSelected()-callback
            final TextView textview = holder.textView;

            // Populate the Spinner
            holder.spinner.setAdapter(new ArrayAdapter<String>(getContext(), android.R.layout.simple_spinner_item, spinnerArray));

            // Add a callback when an item is selected in the Spinner
            holder.spinner.setOnItemSelectedListener(new OnItemSelectedListener() {

                @Override
                public void onItemSelected(AdapterView<?> adapterView, View v, int pos, long id) {
                    // Spinner position is 0-based, so we have to increment 
                    // by one
                    item.setNumberBought(pos + 1);  

                    // Update the total amount in the TextView
                    textview.setText(Integer.toString(item.getCost() * item.getNumberBought()));
                }

                @Override
                public void onNothingSelected(AdapterView<?> arg0) {} // We don't care
            });

            // Set the spinner to the correct position
            // By asking the underlying item how many is bought,
            // the spinner will always show the correct number.
            holder.spinner.setSelection(getItem(position).getNumberBought()-1);
        }   

        return convertView;
    }

    // This guys job is to hold references to the 
    // views we need to access in each row
    private static class ViewHolder {
        public Spinner spinner;
        public TextView textView;
    }
}

How to use it

public class MainActivity extends ListActivity {

    private ShoppingAdapter mAdapter;
    private ArrayList<ShoppingItem> items;

    @SuppressWarnings("unchecked")
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // If savedInstanceState is null, then we have a "fresh" start.
        // Create the 
        if(savedInstanceState == null) {
            items = new ArrayList<ShoppingItem>();
            items.add(new Banana());
            items.add(new Apple());
            items.add(new Banana());
            items.add(new Apple());
            items.add(new Banana());
            items.add(new Apple());
            items.add(new Banana());
        }
        // If savedInstanceState is non-null, we should be able to fetch 
        // the list of items
        else {
            items = (ArrayList<ShoppingItem>) savedInstanceState.getSerializable("items");
        }

        mAdapter = new ShoppingAdapter(this, 0, items);

        getListView().setAdapter(mAdapter);
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);

        // We have to keep our ListView persistent through screen rotations.
        // Lets store the list of items in the "savedInstanceState" Bundle.
        outState.putSerializable("items", items);
    }
}

Getting all the necessary metadata, such as total cost, total number of products, etc., is easy.

@Override
public void onClick(View v) {
    int totalCost = 0;
    int numBananas = 0;
    int numApples = 0;

    int totalNum = mItems.size();

    for(ShoppingItem item : mItems) {
        int numberBought = item.getNumberBought();

        totalCost += item.getCost() * numberBought;

        if(item instanceof Banana) {
            numBananas += numberBought;
        }
        else if(item instanceof Apple) {
            numApples += numberBought;
        }
        // etc, etc
    }
}