new object created every time

Question

I'm developing a shopping cart app in android and a novice. I have been facing one problem now. I can add an item and it adds it to the cart. I can edit the quantity of an item or remove it from the listview after I have added it to the cart.

So what I want is to disable the addToCart button if it is present in the cart already in order to avoid duplicates. But every entry into a product is taken as a new entry. I think I have not referenced it properly. Any help would be appreciated.

This is the Activity that gets called every time you press an item (for example: Dell inside Laptops category)

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.productdetails);
    LayoutInflater li;
    final List<Product> cart = ShoppingCartHelper.getCart();// get all //items from cart
    int productIndex = getIntent().getExtras().getInt(
            ShoppingCartHelper.PRODUCT_INDEX);// the item no in the list
    String PRODUCT_STRING = getIntent().getExtras().getString("PRODUCT");
    switch (PRODUCT_STRING) {
    case "Laptops":
        catalog = ShoppingCartHelper.getLaptopCatalog(getResources())
        break;
    case "Phones":
        catalog = ShoppingCartHelper
                .gePhonesCatalog(getResources());
        break;
    }
    final Product selectedProduct=(Product)this.catalog.get(productIndex);
// this declaration of product is taken as a new entry......................        
    ImageView productImageView = (ImageView) findViewById(R.id.ImageViewProduct);

    productImageView.setImageDrawable(selectedProduct.productImage);    TextView productTitleTextView = (TextView)findViewById(R.id.TextViewProductTitle);

    productTitleTextView.setText(selectedProduct.title);

    TextView productDetailsTextView = (TextView) findViewById(R.id.TextViewProductDetails);

    productDetailsTextView.setText(selectedProduct.description);

    final Button addToCartButton = (Button) findViewById(R.id.ButtonAddToCart);

    addToCartButton.setOnClickListener(new OnClickListener() {
        @Override

        public void onClick(View v) {
            cart.add(selectedProduct);
                selectedProduct.quantity ++;
            finish();
        }
    });     
    if(cart.contains(selectedProduct)) {
           addToCartButton.setEnabled(false);
           addToCartButton.setText("Item in Cart");
    }       
}

Answer 1

The fastest workaround to this would be to override the item's equals() .

Otherwise, every instance of your item will be considered (and really is ) different from Java's perspective.

Here's how you could do it:

// Somewhere in your item's class..

@Override
public boolean equals(Object o) {
    if(!(o instanceof YourItem)
        return false;
    YourItem i = (YourItem) o;
    // This line below is based on my assumption, you should change to better suit your usecase.
    return this.getItemId() == i.getItemId();
}

Of course in above code I assume that your item has a field for an item ID and a getter method to obtain it. Do note that it might not suit you and that you might have to make some adaptation to it.