android.support.v7.widget.GridLayoutManager#findLastVisibleItemPosition ( )源码实例Demo

/**
 * 刷新所能看到的选择
 */
public void refreshSelection() {
    GridLayoutManager layoutManager = (GridLayoutManager) mRecyclerView.getLayoutManager();
    // 获取当前能看到的第一个，和最后一个
    int first = layoutManager.findFirstVisibleItemPosition();
    int last = layoutManager.findLastVisibleItemPosition();
    if (first == -1 || last == -1) {
        // 如果是-1就直接返回
        return;
    }
    // 获取数据源
    Cursor cursor = getCursor();
    for (int i = first; i <= last; i++) {
        RecyclerView.ViewHolder holder = mRecyclerView.findViewHolderForAdapterPosition(first);
        if (holder instanceof MediaViewHolder) {
            if (cursor.moveToPosition(i)) {
                setCheckStatus(MultiMedia.valueOf(cursor), ((MediaViewHolder) holder).mMediaGrid);
            }
        }
    }
}
 

public void refreshSelection() {
    GridLayoutManager layoutManager = (GridLayoutManager) mRecyclerView.getLayoutManager();
    int first = layoutManager.findFirstVisibleItemPosition();
    int last = layoutManager.findLastVisibleItemPosition();
    if (first == -1 || last == -1) {
        return;
    }
    Cursor cursor = getCursor();
    for (int i = first; i <= last; i++) {
        RecyclerView.ViewHolder holder = mRecyclerView.findViewHolderForAdapterPosition(first);
        if (holder instanceof MediaViewHolder) {
            if (cursor.moveToPosition(i)) {
                setCheckStatus(Item.valueOf(cursor), ((MediaViewHolder) holder).mMediaGrid);
            }
        }
    }
}
 

@Override
public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
    if (dy < 0 || loadMoreSubject == null || loadMoreSubject.isLoading()){
        return;
    }

    int lastItem = 0;
    RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
    int totalItemCount = layoutManager.getItemCount();
    if (layoutManager instanceof GridLayoutManager) {
        GridLayoutManager gridLayoutManager = ((GridLayoutManager) layoutManager);
        //Position to find the final item of the current LayoutManager
        lastItem = gridLayoutManager.findLastCompletelyVisibleItemPosition();
        if (lastItem == -1){
            lastItem = gridLayoutManager.findLastVisibleItemPosition();
        }
    } else if (layoutManager instanceof LinearLayoutManager) {
        LinearLayoutManager linearLayoutManager = ((LinearLayoutManager) layoutManager);
        lastItem = linearLayoutManager.findLastCompletelyVisibleItemPosition();
        if (lastItem == -1){
            lastItem = linearLayoutManager.findLastVisibleItemPosition();
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        StaggeredGridLayoutManager staggeredGridLayoutManager = ((StaggeredGridLayoutManager) layoutManager);
        // since may lead to the final item has more than one StaggeredGridLayoutManager the particularity of the so here that is an array
        // this array into an array of position and then take the maximum value that is the last show the position value
        int[] lastPositions = staggeredGridLayoutManager.findLastCompletelyVisibleItemPositions(null);
        lastItem = findMax(lastPositions);
    }
    final int childCount = layoutManager.getChildCount();
    final boolean shouldLoadMore = (childCount > 0 && lastItem >= totalItemCount - VISIBLE_THRESHOLD);
    if (shouldLoadMore) {
        loadMoreSubject.onLoadMore();
    }
}
 

private void doClickOtherToNavigation(ViewGroup parent, int position, MyViewHolder myHolder) {
    RecyclerView recyclerView = (RecyclerView) parent;
    LayoutManager manager = recyclerView.getLayoutManager();
    View currentView = manager.findViewByPosition(myHolder.getAdapterPosition());
    View preTargetView = manager.findViewByPosition(this.mTopSize);
    GridLayoutManager gridLayoutManager = (GridLayoutManager) manager;
    int spanCount = gridLayoutManager.getSpanCount();
    int targetPosition = this.mTopSize + 1;
    if (recyclerView.indexOfChild(preTargetView) >= 0) {
        int targetX = preTargetView.getLeft();
        int targetY = preTargetView.getTop();
        if ((targetPosition - 1) % spanCount == 0) {
            View targetView = manager.findViewByPosition(targetPosition);
            targetX = targetView.getLeft();
            targetY = targetView.getTop();
        } else {
            targetX += preTargetView.getWidth() + UIsUtils.dipToPx(TitleBar.SHAREBTN_RIGHT_MARGIN);
            if (gridLayoutManager.findLastVisibleItemPosition() == getItemCount() - 1 && (((getItemCount() - 1) - this.mTopSize) - 2) % spanCount == 0) {
                if (gridLayoutManager.findFirstVisibleItemPosition() != 0) {
                    targetY += preTargetView.getHeight() + UIsUtils.dipToPx(TitleBar.SHAREBTN_RIGHT_MARGIN);
                } else if (gridLayoutManager.findFirstCompletelyVisibleItemPosition() != 0) {
                    targetY += (-recyclerView.getChildAt(0).getTop()) - recyclerView.getPaddingTop();
                }
            }
        }
        moveOtherToMy(myHolder);
        startAnimation(recyclerView, currentView, (float) targetX, (float) targetY);
        return;
    }
    moveOtherToMy(myHolder);
    int index = (this.mTopSize % spanCount) - 1;
    if (index < 0) {
        index = spanCount - 1;
    }
    startAnimation(recyclerView, currentView, (float) ((currentView.getWidth() * index) + (index == 0 ? 0 : (index - 1) * UIsUtils.dipToPx(TitleBar.SHAREBTN_RIGHT_MARGIN))), 0.0f);
}
 

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
  super.onScrolled(recyclerView, dx, dy);
  RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
  if(listener == null){
    return;
  }
  IOnLoadMoreListener iOnLoadMoreListener = listener.get();

  if(iOnLoadMoreListener!=null) {

    iOnLoadMoreListener.onBeforeScroll(dx, dy);

    if (layoutManager instanceof LinearLayoutManager) {
      layoutManagerType = LAYOUT_MANAGER_TYPE.LINEAR;
      LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
      mLastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition();
      int firstVisible = linearLayoutManager.findFirstVisibleItemPosition();
      iOnLoadMoreListener.notifyAppearStateChange(firstVisible
          , mLastVisibleItemPosition
          , dx
          , dy);
    } else if (layoutManager instanceof GridLayoutManager) {
      layoutManagerType = LAYOUT_MANAGER_TYPE.GRID;
      GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
      mLastVisibleItemPosition = gridLayoutManager.findLastVisibleItemPosition();
      iOnLoadMoreListener.notifyAppearStateChange(gridLayoutManager.findFirstVisibleItemPosition()
          , mLastVisibleItemPosition
          , dx
          , dy);

    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
      layoutManagerType = LAYOUT_MANAGER_TYPE.STAGGERED_GRID;
      StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) layoutManager;
      int newSpanCount = staggeredGridLayoutManager.getSpanCount();
      if (mLastPositions == null || newSpanCount != mLastPositions.length) {
        mLastPositions = new int[newSpanCount];
      }
      if (mFirstPositions == null || newSpanCount != mFirstPositions.length) {
        mFirstPositions = new int[newSpanCount];
      }
      //avoid crash of support-v7 original bug
      try{
        staggeredGridLayoutManager.findFirstVisibleItemPositions(mFirstPositions);
        mFirstVisibleItemPosition = findMin(mFirstPositions);
        staggeredGridLayoutManager.findLastVisibleItemPositions(mLastPositions);
        mLastVisibleItemPosition = findMax(mLastPositions);
        iOnLoadMoreListener.notifyAppearStateChange(
            mFirstVisibleItemPosition
            , mLastVisibleItemPosition
            , dx
            , dy);

      }catch(Exception e){
        e.printStackTrace();
        WXLogUtils.e(e.toString());
      }

    } else {
      throw new RuntimeException(
          "Unsupported LayoutManager used. Valid ones are LinearLayoutManager, GridLayoutManager and StaggeredGridLayoutManager");
    }
  }
}