this.changedHandler = function(currentItem){
        console.log("Categoryamount before:");
        console.log(self.categoryAmount());
        // Maak categoryAmount leeg
        self.categoryAmount.removeAll();
        // Vul category amount weer
        for(var i = 0; i< self.cart().length; i++){
            var currentCartItem = self.cart()[i];
            // check if category already is in array
            var existingCategory = ko.utils.arrayFirst(self.categoryAmount(), function(item) {
            return currentCartItem.product().categoryId === item.categoryId();
            });

            if(existingCategory !== null){
                existingCategory.amount(existingCategory.amount() + currentCartItem.amount);
            }else{
                self.categoryAmount.push( new SelectedCategory(currentCartItem .product().categoryId, currentCartItem.amount));
            }
        }
        console.log("Categoryamount after:");
        console.log(self.categoryAmount());
    };