Update activity's TextView from EditText value within ListView's item

Question

So, I have an activity with a TextView and a ListView with a custom BaseAdapter. This activity looks like this:

As you can see, every item of the list is a custom layout and the basic idea is: every time the numeric EditText within it changes, the "total" TextView from the activity (which is the sum of the prices of every product) must be updated as well.

I suppose it must somehow be done from the Adapter class, but I don't know how to do it.

My Activity file looks like this (it gets products data from server via "GetCollectionProducts" AsyncTask, where I set the adapter):

public class ProductAisleActivity extends AppCompatActivity implements View.OnClickListener{
ListView productList;
Button participate;

ImageButton search;
EditText searchET;
TextView productsTotal;

Product[] colProducts;
RelativeLayout collectionHeader;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_product_aisle);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    /* ...
       Irrelevant code to this question 
    */

    productsTotal = (TextView) findViewById(R.id.products_aisle_total);
    productsTotal.setText(
            getResources().getString(
                    R.string.productsTotal,
                    String.valueOf(0.00)
            )
    );

    productList = (ListView) findViewById(R.id.products_aisle_list);
    new GetCollectionProducts().execute();
}

private class GetCollectionProducts extends AsyncTask<Void,Void,JSONArray>{

    @Override
    protected JSONArray doInBackground(Void... voids) {
        /* Irrelevant code to this question */
    }

    @Override
    protected void onPostExecute(JSONArray jsonArray) {
        /* Irrelevant code to this question */
                productList.setAdapter(
                        new CollectionProductsAdapter(
                                ProductAisleActivity.this,
                                colProducts
                        )
                );
}
}

And my Adapter file looks as follows:

public class CollectionProductsAdapter extends BaseAdapter {
Context context;
ProductAisleActivity.Product[] data;
private static LayoutInflater inflater = null;

public CollectionProductsAdapter(Context context, ProductAisleActivity.Product[] data) {
    this.context = context;
    this.data = data;
    inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public int getCount() {
    return data.length;
}

@Override
public Object getItem(int i) {
    return data[i];
}

@Override
public long getItemId(int i) {
    return i;
}

@Override
public View getView(int i, View view, ViewGroup viewGroup) {
    View v = view;
    if (v == null) {
        v = inflater.inflate(R.layout.product_row_layout, null);
    }

    ProductAisleActivity.Product product = data[i];

    /* ...
       Irrelevant code to this question 
    */

    EditText productQuantity = (EditText) v.findViewById(R.id.productQuantity);
    productQuantity.setText("0");


    return v;
}

}

I'm stuck at this point, any help will be appreciated.

Answer 1

First you need to listen for any changes in the EditText so you can handle things dynamically without explicitly using something like a submit button. You can do this with a TextWatcher.

productQuanity.addTextChangedListener(new TextWatcher() {
        private double originalCost = 0.0;

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            // Before we change the text, set the originalCost
            // so we can know what the change is after the edit
            originalCost = getCost(s.toString());
        }

        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            // You don't need to utilize this method
        }

        @Override
        public void afterTextChanged(Editable s) {
             // After the change has taken place in the text,
             // get the new cost and calculate the difference
             double newCost = getCost(s.toString());
             double changeInCost = newCost - originalCost;
        }

        private double getCost(String input){
            String count = input.toString();
            if(TextUtils.isEmpty(count))
                return 0.0;
            else
                return (double) Integer.parseInt(count) * product.getPrice();
        }
    });

Now that we have the change in cost, what do we do with it? We need to notify the activity that we have a change. We can do that with an observer, which is fine, but for fun let's use an interface to implement a listener.

Modify your adapter class

public class CollectionProductsAdapter extends BaseAdapter {

    public interface CostChangedListener{
        void onCostChanged(double change);
    }

    Context context;
    ProductAisleActivity.Product[] data;
    private LayoutInflater inflater = null; // THIS SHOULDN'T BE STATIC
    CostChangedListener listener;

    public CollectionProductsAdapter(Context context, ProductAisleActivity.Product[] data, CostChangedListener listener) {
        this.context = context;
        this.data = data;
        inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        this.listener = listener;
    }

    // The rest of your code
}

Now when we update the cost in our TextWatcher we can call

if(listener != null)
    listener.onCostChanged(changeInCost);

Last, to make sure we utilize this correctly, we will need to pass a listener in our CollectionProductsAdapter constructor

productList.setAdapter(new CollectionProductsAdapter(
            ProductAisleActivity.this, colProducts,
            new CostChangeListener(){
                @Override
                public void onCostChanged(double change){
                    double currentTotal = Double.valueOf(productTotal.getText());
                    double newTotal = currentTotal + change;
                    productTotal.setText(String.valueOf(newTotal));
                }));

Obviously you may need to tweak some of this to get it to match perfectly, and I haven't tested it so some things might be off a bit, but this should get you going in the right direction. If you have any issue feel free to comment and I will try to help you through it.

Notes

1. Do not keep a static reference like you were with your layout inflater
2. It is worth taking a look at the RecyclerView or at least the ViewHolder pattern with an Adapter

Answer 2

You want to add a textChangedListener for changing item values as user changes values in EditText.

You can use TextChangedListener here:

EditText myEditTextField = new EditText(this);

myEditTextField.addTextChangedListener(new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {

    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {

    }

    @Override
    public void afterTextChanged(Editable s) {

    }
});

You can perform tasks according to your need. It has 3 methods:

1.beforeTextChanged

2.onTextChanged

3.afterTextChanged

So you can get your task done by the help of "afterTextChanged". You have to simply call your method of calculating price for no. of items when user enters a particular number.And it will show you the price as you want.

Hope this help!