How to get center object after RecyclerView snap it to center?

Question

I implement a horizontal RecyclerViewone that snaps items to the center after scrolling, such as the Google play App horizontal lists. This is an overview.

My code is below:

MainMenuAdapter mainMenuAdapter = new MainMenuAdapter(this, mDataset);

final LinearLayoutManager layoutManagaer = new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);

RecyclerView mainMenu = (RecyclerView) findViewById(R.id.main_menu);
mainMenu.setLayoutManager(layoutManagaer);
mainMenu.setAdapter(mainMenuAdapter);

final SnapHelper snapHelper = new LinearSnapHelper();
snapHelper.attachToRecyclerView(mainMenu);     
snapHelper.attachToRecyclerView(mainMenu);

How can I get the center position (position) after RecyclerView, tying it to the center? Is there really no listener opportunity for this? Also, when I need to touch an element, I want to snap it to the center. How can i do this?

Answer 1

if you need a view you can call

 View view =  snapHelper.findSnapView(layoutManagaer);

, , . ,

   mainMenu.getChildAdapterPosition(view)

Answer 2

SnapHelper, RecyclerView.OnScrollListener.

• MiddleItemFinder .

• MiddleItemCallback.

  MiddleItemFinder.MiddleItemCallback callback = 
          new MiddleItemFinder.MiddleItemCallback() {
                  @Override
                  public void scrollFinished(int middleElement) {
                      // interaction with middle item
                  }
  };
  

• RecyclerView

  recyclerView.addOnScrollListener(
          new MiddleItemFinder(getContext(), layoutManager, 
                  callback, RecyclerView.SCROLL_STATE_IDLE));
  

• MiddleItemFinder scrollState.

  • RecyclerView.SCROLL_STATE_IDLE - RecyclerView . .
  • RecyclerView.SCROLL_STATE_DRAGGING - RecyclerView , .
  • RecyclerView.SCROLL_STATE_SETTLING - RecyclerView , .
  • MiddleItemFinder.ALL_STATES - .
• , RecyclerView.SCROLL_STATE_IDLE , , .

MiddleItemFinder:

public class MiddleItemFinder extends RecyclerView.OnScrollListener {

    private
    Context context;

    private
    LinearLayoutManager layoutManager;

    private
    MiddleItemCallback callback;

    private
    int controlState;

    public
    static final int ALL_STATES = 10;

    public MiddleItemFinder(Context context, LinearLayoutManager layoutManager, MiddleItemCallback callback, int controlState) {
    this.context = context;
    this.layoutManager = layoutManager;
    this.callback = callback;
    this.controlState = controlState;
    }

    @Override
    public void onScrollStateChanged(RecyclerView recyclerView, int newState) {

        if (controlState == ALL_STATES || newState == controlState) {

            int firstVisible = layoutManager.findFirstVisibleItemPosition();
            int lastVisible = layoutManager.findLastVisibleItemPosition();
            int itemsCount = lastVisible - firstVisible + 1;

            int screenCenter = context.getResources().getDisplayMetrics().widthPixels / 2;

            int minCenterOffset = Integer.MAX_VALUE;

            int middleItemIndex = 0;

            for (int index = 0; index < itemsCount; index++) {

                View listItem = layoutManager.getChildAt(index);

                if (listItem == null)
                    return;

                int leftOffset = listItem.getLeft();
                int rightOffset = listItem.getRight();
                int centerOffset = Math.abs(leftOffset - screenCenter) + Math.abs(rightOffset - screenCenter);

                if (minCenterOffset > centerOffset) {
                    minCenterOffset = centerOffset;
                    middleItemIndex = index + firstVisible;
                }
            }

            callback.scrollFinished(middleItemIndex);
        }
    }

    public interface MiddleItemCallback {

        void scrollFinished(int middleElement);
    }
}