The correct way of implementing getItemId() in RecyclerView.Adapter

问题

I have generic class

public abstract class BaseAdapter<T> extends RecyclerView.Adapter {
  private List<T> itemsList = new ArrayList<>();
  //other override methods

  @Override
    public long getItemId(int position) {
        return position;
    }
}

What is the correct way to implementing getItemId()? I think that return position like in many example is not correct.

回答1:

1. Create a base interface that has a method that returns a type long eg.

   interface BaseInterface{
       long getId(); 
   }
   

2. Change

   abstract class BaseAdapter<T> extends RecyclerView.Adapter 
   

   to

   abstract class BaseAdapter<T extends BaseInterface> extends RecyclerView.Adapter {
   

   Note: The signature changed to T extends BaseInterface

3. Replace

   @Override
   public long getItemId(int position) {
       return position;
   }
   

   with

   @Override
   public long getItemId(int position) {
       return itemsList.get(position).getId();
   }
   

回答2:

In the List you could only return the Id of the Item available at specific row as mentioned by Google documents:

getItemId

Get the row id associated with the specified position in the list.

But that's not the case with RecyclerView, in RecyclerView you have to ensure that you either return a unique Id for each Item or In case of no Stable Id you should return RecyclerView.NO_ID (-1). Please Refrain from returning values that are not stable. (An Stable value would be a unique value that does not change even if position of dataset changes)

回答3:

you should implement this methode: as you see you must tell the Adapter that you implemented that by setHasStableIds(true);

class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
MyAdapter() {
    setHasStableIds(true); // **very importent**
}

@Override
public long getItemId(int position) {
    // requires static value, it means need to keep the same value
    // even if the item position has been changed.
    return mItems.get(position).getId();
}

}

来源：https://stackoverflow.com/questions/42646950/the-correct-way-of-implementing-getitemid-in-recyclerview-adapter