button_add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(this, ProductActivity.class);
                startActivity(intent);

                Bundle arguments = getIntent().getExtras();

                if(arguments!=null){
                    productList.add(new Product(4, arguments.get("name").toString()));
                    productArrayAdapter.notifyDataSetChanged();
                }

            }
        }); 

button_add_product = (ImageButton) findViewById(R.id.button_add_product);

        button_add_product.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Product product = new Product(-1, "");

                Intent intent = new Intent(MainActivity.this, ProductActivity.class);
                intent.putExtra(Product.class.getSimpleName(), product);
                startActivity(intent);
            }
        });

Product product;

        Bundle arguments = getIntent().getExtras();

        if(arguments != null) {
            product = (Product) arguments.getSerializable(Product.class.getSimpleName());
            productID.setText(Integer.toString(product.id));
//            productID.setText(arguments.get("productID").toString());
        } else {
            product = new Product(-1, "");
        }

button_save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                product.id = Integer.parseInt((productID.getText().toString()));
                if (productName.getText().toString().trim() == "")
                    product.name = new String("Нет названия");
                else
                    product.name = productName.getText().toString();

                Intent intent = new Intent(ProductActivity.this, MainActivity.class);
                intent.putExtra(Product.class.getSimpleName(), product);
                intent.putExtra("method","product_add");
                startActivity(intent);
            }
        }); 

@Override
    protected void onRestart() {
        super.onRestart();

        Bundle arguments = getIntent().getExtras();

        if(arguments != null) {
            if (arguments.get("method").toString() == "product_add") {
                Product product = (Product) arguments.getSerializable(Product.class.getSimpleName());

                productList.add(product);
                productArrayAdapter.notifyDataSetChanged();
            }

//            productID.setText(arguments.get("productID").toString());
        }
    }