如何在顶部显示特定的recyclerview项目？

Question

Let's say I have web-request for a list of meals and implemented using a Recyclerview, now what if I want to sort/move specific items at the top..!

---

Meal: Italian Pasta | Type: pasta | Price: 20$

Meal: Hotdogs Pizza | Type: pizza | Price: 10$

Meal: Burger | Type: fast food | Price: 30$

Meal: Rice | Type: lunch | Price: 18$

Meal: Mac & Cheese | Type: lunch | Price: 17$

Meal: CheeseBurger | Type: fast food | Price: 8$

---

So for example, what I want is for every item who has a type of fast food and pizza to show at the top of the list and then the rest..!?

where do I perform this sorting logic, is it inside the adapter or the activity of the recyclerview? is there like an existing method for this function like moveToTop() to be used like this:

for(Meals item: dataList){

   if (item.getType.equals("fast food") || item.getType.equals("pizza")){
      item.moveToTop(); 
   }

}

Is it possible?

---

Update 2

I figured out, I found a method a special parameter of interface for the recyclerview in these situations SortedListAdapterCallback

if (homeData.size() > 0) {

            Collections.sort(homeData, Collections.reverseOrder(new SortedListAdapterCallback<HomeItemModel>(adapter) {
              @Override
              public int compare(HomeItemModel o1, HomeItemModel o2) {

               int weight1;
               int weight2;

               if(item1.getType.equals("fast food") || item1.getType.equals("pizza")){
                   weight1 = 1;
               }else{
                   weight1 = 0;
               }

               if(item2.getType.equals("fast food") || item2.getType.equals("pizza")){
                weight2 = 1;
               }else{
                weight2 = 0;
               }

                if (weight1 == weight2)
                   return 0;
                else if (weight1 > weight2)
                   return 1;
                else
                   return -1;

                 }

              @Override
              public boolean areContentsTheSame(HomeItemModel oldItem, HomeItemModel newItem) {
                return false;
              }

              @Override
              public boolean areItemsTheSame(HomeItemModel item1, HomeItemModel item2) {
                return false;
              }
            }));

          }

The only problem here, is the order at the top..! they show like this:

• fast food
• pizza
• pizza
• fast food
• pizza
• fast food
• ... the rest of the list

I want them to show ordered.. like this:

• fast food // or the pizzas first
• fast food
• fast food
• pizza
• pizza
• pizza
• ... the rest of the list

Can this be done..?

Answer 1

Create a Comparator inside your POJO class Meals

public static class CustomComparator implements Comparator<Meals> {
    public int compare(Meals  item1, Meals  item2) {

        int weight1;
        int weight2;

        if(item1.getType.equals("fast food") || item1.getType.equals("pizza")){
            weight1 = 1;
        }else{
            weight1 = 0;
        }

        if(item2.getType.equals("fast food") || item2.getType.equals("pizza")){
            weight2 = 1;
        }else{
            weight2 = 0;
        }


        if (weight1 == weight2)
            return 0;
        else if (weight1 > weight2)
            return 1;
        else
            return -1;
    }
}

And before setting your adapter call this line then pass the data list into your Adapter constructor.

Collections.sort(yourDataLIst, Collections.reverseOrder(new Meals.CustomComparator()));

EDIT If you want to all fast food first then pizza and then all the list then just tweak your sort logic as below

        if(item1.getType.equals("fast food")){
            weight1 = 2;
        }else if (item1.getType.equals("pizza")){
            weight1 = 1;
        } else {
            weight1 = 0;
        }

        if(item2.getType.equals("fast food")){
            weight2 = 2;
        }else if (item2.getType.equals("pizza")){
            weight2 = 1;
        } else{
            weight2 = 0;
        }

Answer 2

There is no simple method like moveToTop() in Arraylist . But you can shift the data manually.

You can do that like this:

for(Meals item: dataList){

   if (item.getType.equals("fast food") || item.getType.equals("pizza")){
      int index = dataList.indexOf(item);
      dataList.remove(index);
      dataList.add(0, item);
      adapter.notifyDataSetChanged()
   }

}

Hope it helps:)