Pick random data list

Hi, i have any problem. when will pick item random :
when i pick key item list result random. i receive message failed.
please, helpme .

var item = find.byType('ListView').finderType.length;
print(item);
Random random = new Random();
var result = random.nextInt(item - 0);
print(result);
var pickProduct = 'listProduk' + result.toString();
print (pickProduct);
var produk = find.byValueKey(pickProduct).finderType.length;
print(produk);