androidx.recyclerview.widget.RecyclerView#NO_POSITION源码实例Demo

private void checkScrollForLoad(boolean scroll) {
    if (chatLayoutManager == null || paused) {
        return;
    }
    int firstVisibleItem = chatLayoutManager.findFirstVisibleItemPosition();
    int visibleItemCount = firstVisibleItem == RecyclerView.NO_POSITION ? 0 : Math.abs(chatLayoutManager.findLastVisibleItemPosition() - firstVisibleItem) + 1;
    if (visibleItemCount > 0) {
        int totalItemCount = chatAdapter.getItemCount();
        int checkLoadCount;
        if (scroll) {
            checkLoadCount = 25;
        } else  {
            checkLoadCount = 5;
        }
        if (firstVisibleItem <= checkLoadCount && !loading && !endReached) {
            loadMessages(false);
        }
    }
}
 

@Override
public void itemSwiped(int position, int direction) {
    ContentItem item = itemAdapter.getAdapterItem(position);
    item.setSwipeDirection(direction);

    if (item.getContent() != null) {
        Debouncer<Content> deleteDebouncer = new Debouncer<>(2000, this::onDeleteBook);
        deleteDebouncer.submit(item.getContent());

        Runnable cancelSwipe = () -> {
            deleteDebouncer.clear();
            item.setSwipeDirection(0);
            int position1 = itemAdapter.getAdapterPosition(item);
            if (position1 != RecyclerView.NO_POSITION)
                fastAdapter.notifyItemChanged(position1);
        };
        item.setUndoSwipeAction(cancelSwipe);
        fastAdapter.notifyItemChanged(position);
    }
}
 

static <K> FocusDelegate<K> dummy() {
    return new FocusDelegate<K>() {
        @Override
        public void focusItem(@NonNull ItemDetails<K> item) {
        }

        @Override
        public boolean hasFocusedItem() {
            return false;
        }

        @Override
        public int getFocusedPosition() {
            return RecyclerView.NO_POSITION;
        }

        @Override
        public void clearFocus() {
        }
    };
}
 

@Override
public void onClick(View v) {
    int pos = getAdapterPosition();
    if (pos == RecyclerView.NO_POSITION)
        return;

    TupleFolderNav folder = items.get(pos);
    if (folder == null)
        return;

    LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(context);
    lbm.sendBroadcast(
            new Intent(ActivityView.ACTION_VIEW_MESSAGES)
                    .putExtra("account", folder.account)
                    .putExtra("folder", folder.id)
                    .putExtra("type", folder.type));
}
 

@Override
public void itemSwiped(int position, int direction) {
    ContentItem item = getItemAdapter().getAdapterItem(position);

    item.setSwipeDirection(direction);

    if (item.getContent() != null) {
        Debouncer<ContentItem> deleteDebouncer = new Debouncer<>(2000, this::onDeleteSwipedBook);
        deleteDebouncer.submit(item);

        Runnable cancelSwipe = () -> {
            deleteDebouncer.clear();
            item.setSwipeDirection(0);

            int position1 = getItemAdapter().getAdapterPosition(item);
            if (position1 != RecyclerView.NO_POSITION)
                fastAdapter.notifyItemChanged(position1);
        };
        item.setUndoSwipeAction(cancelSwipe);
        fastAdapter.notifyItemChanged(position);
    }
}
 

@Override
  public void onClick(View v) {

    Object tag = v.getTag();
    if (tag instanceof RecyclerView.ViewHolder) {
      int flatPosition = ((RecyclerView.ViewHolder) v.getTag()).getAdapterPosition();

      if (flatPosition == RecyclerView.NO_POSITION) {
        return;
      }

      long expandablePosition = mExpandableItemManager.getExpandablePosition(flatPosition);
      int groupPosition = RecyclerViewExpandableItemManager
          .getPackedPositionGroup(expandablePosition);
//      int childPosition = RecyclerViewExpandableItemManager
//          .getPackedPositionChild(expandablePosition);

      switch (v.getId()) {
        case R.id.layout_group_item:
          // toggle expanded/collapsed
          if (mExpandableItemManager.isGroupExpanded(groupPosition)) {
            mExpandableItemManager.collapseGroup(groupPosition);
          } else {
            mExpandableItemManager.expandGroup(groupPosition);
          }
          break;
        case R.id.img_menu_ups:
          if (mOnGroupOtherClickListener != null) {
            mOnGroupOtherClickListener.onOtherClick(groupPosition, v);
          }
          break;
      }
    }

    if (v.getTag() instanceof ChildViewHolder) {
      ((ChildViewHolder) v.getTag()).switchCompat.toggle();
    }
  }
 

@Override
public int getPreferenceAdapterPosition(Preference preference) {
    final int size = mPreferenceList.size();
    for (int i = 0; i < size; i++) {
        final Preference candidate = mPreferenceList.get(i);
        if (candidate != null && candidate.equals(preference)) {
            return i;
        }
    }
    return RecyclerView.NO_POSITION;
}
 

private int findItemPositionById(long id) {
    final int first = mMessageViewLayoutManager.findFirstVisibleItemPosition();
    final int last = mMessageViewLayoutManager.findLastVisibleItemPosition();
    if (last == RecyclerView.NO_POSITION) {
        return -1;
    }

    return mMessagesAdapter.findItemPositionById(id, first, last);
}
 

protected int getHeaderTop(RecyclerView parent, View child, View header, int adapterPos,
                         int layoutPos)
{
  int headerHeight = getHeaderHeightForLayout(header);
  int top = getChildY(parent, child) - headerHeight;
  if (sticky && layoutPos == 0) {
    final int count = parent.getChildCount();
    final long currentId = adapter.getHeaderId(adapterPos);
    // find next view with header and compute the offscreen push if needed
    for (int i = 1; i < count; i++) {
      int adapterPosHere = parent.getChildAdapterPosition(parent.getChildAt(translatedChildPosition(parent, i)));
      if (adapterPosHere != RecyclerView.NO_POSITION) {
        long nextId = adapter.getHeaderId(adapterPosHere);
        if (nextId != currentId) {
          final View next = parent.getChildAt(translatedChildPosition(parent, i));
          final int offset = getChildY(parent, next) - (headerHeight + getHeader(parent, adapter, adapterPosHere).itemView.getHeight());
          if (offset < 0) {
            return offset;
          } else {
            break;
          }
        }
      }
    }

    if (sticky) top = Math.max(0, top);
  }

  return top;
}
 

public void setSelectedLabel(final Label label) {
    if ((label == null && this.selectedLabel == null) || (same(label, this.selectedLabel))) {
        return;
    }
    final int previous = getPosition(this.selectedLabel);
    final int position = getPosition(label);
    this.selectedLabel = label;
    if (previous != RecyclerView.NO_POSITION) {
        notifyItemChanged(previous);
    }
    if (position != RecyclerView.NO_POSITION) {
        notifyItemChanged(position);
    }
}
 

/**
 * Gets the activated position only when mode is {@code SINGLE}.
 *
 * @return the activated position when {@code SINGLE}. -1 if no item is selected
 * @since 1.0.0-b1
 */
public int getActivatedPosition() {
    List<Integer> selectedPositions = mAdapter.getSelectedPositions();
    if (mAdapter.getMode() == Mode.SINGLE && selectedPositions.size() == 1) {
        return selectedPositions.get(0);
    }
    return RecyclerView.NO_POSITION;
}
 

private void changeItem(View view) {
    int position = mRecyclerView.getChildAdapterPosition(view);
    if (position != RecyclerView.NO_POSITION) {
        int color = generateColor();
        mColors.set(position, color);
        notifyItemChanged(position);
    }
}
 

private void updateStickyLayout(int position)
{
    if (position == RecyclerView.NO_POSITION)
    {
        return;
    }

    RcvSectionWrapper wrapper = (RcvSectionWrapper) mAdapter.getDatas().get(position - mAdapter.getHeadCounts());
    mAdapter.onBindSectionLabelView(mHolder, wrapper.getSection(), position);
    mCurrentIndicatePosition = position;
}
 

@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
    super.getItemOffsets(outRect, view, parent, state);
    int itemPosition = parent.getChildAdapterPosition(view);
    if (itemPosition == RecyclerView.NO_POSITION) {
        return;
    }
    if (mHeaderPositionCalculator.hasNewHeader(itemPosition)) {
        View header = getHeaderView(parent, itemPosition);
        setItemOffsetsForHeader(outRect, header, mOrientationProvider.getOrientation(parent));
    }
}
 

int getConvertedPosition(int sectionedPosition) {
  if (isSectionHeaderPosition(sectionedPosition)) {
    return RecyclerView.NO_POSITION;
  }

  int offset = 0;
  for (int i = 0; i < sections.size(); i++) {
    if (sections.valueAt(i).sectionedPosition > sectionedPosition) {
      break;
    }
    --offset;
  }
  return sectionedPosition + offset;
}
 

@Override
public int getScrollOffset() {
    int firstItemPosition = getFirstItemPosition();
    if (firstItemPosition == RecyclerView.NO_POSITION) {
        return 0;
    }
    int itemHeight = getItemHeight();
    int firstItemTop = getFirstItemOffset();
    return mView.getPaddingTop() + firstItemPosition * itemHeight - firstItemTop;
}
 

private int calculateGroupOffset(RecyclerView parent, long currentHeaderId, int nextPosition) {
    if (mExpandableAdapter == null) return 0;
    int adapterPosHere = parent.getChildAdapterPosition(parent.getChildAt(nextPosition));
    if (adapterPosHere != RecyclerView.NO_POSITION) {
        long nextId = mExpandableAdapter.getGroupUniqueId(adapterPosHere);
        if (nextId != currentHeaderId && nextId != NO_STICKY_ID) {
            View next = parent.getChildAt(nextPosition);
            RecyclerView.ViewHolder viewHolder = getGroupHeader(parent, adapterPosHere);
            if (viewHolder == null) return OFFSET_NOT_FOUND;
            return (int) next.getY() - viewHolder.itemView.getHeight();
        }
    }
    return OFFSET_NOT_FOUND;
}
 

/**
 * 绘制悬浮组
 *
 * @param c      Canvas
 * @param parent RecyclerView
 */
protected void onDrawOverGroup(Canvas c, RecyclerView parent) {
    int firstVisiblePosition = ((LinearLayoutManager) parent.getLayoutManager()).findFirstVisibleItemPosition();
    if (firstVisiblePosition == RecyclerView.NO_POSITION) {
        return;
    }
    Group group = getCroup(firstVisiblePosition);
    if (group == null)
        return;
    String groupTitle = group.toString();
    if (TextUtils.isEmpty(groupTitle)) {
        return;
    }
    boolean isRestore = false;
    Group nextGroup = getCroup(firstVisiblePosition + 1);
    if (nextGroup != null && !group.equals(nextGroup)) {
        //说明是当前组最后一个元素，但不一定碰撞了
        View child = parent.findViewHolderForAdapterPosition(firstVisiblePosition).itemView;
        if (child.getTop() + child.getMeasuredHeight() < mGroupHeight) {
            //进一步检测碰撞
            c.save();//保存画布当前的状态
            isRestore = true;
            c.translate(0, child.getTop() + child.getMeasuredHeight() - mGroupHeight);
        }
    }
    int left = parent.getPaddingLeft();
    int right = parent.getWidth() - parent.getPaddingRight();
    int top = parent.getPaddingTop();
    int bottom = top + mGroupHeight;
    c.drawRect(left, top, right, bottom, mBackgroundPaint);
    float x;
    float y = top + mTextBaseLine;
    if (isCenter) {
        x = parent.getMeasuredWidth() / 2 - getTextX(groupTitle);
    } else {
        x = mPaddingLeft;
    }
    c.drawText(groupTitle, x, y, mTextPaint);
    if (isRestore) {
        //还原画布为初始状态
        c.restore();
    }
}
 

public void changeItem(int position, T item) {
    if (position != RecyclerView.NO_POSITION && item != null) {
        mItemList.set(position, item);
        notifyItemChanged(position);
    }
}
 

/**
 * Overcomes the situation of returning an unknown position (-1) of ViewHolders created out of
 * the LayoutManager (ex. StickyHeaders).
 * <p><b>NOTE:</b> Always call this method, instead of {@code getAdapterPosition()}, in case
 * of StickyHeaders use case.</p>
 *
 * @return the Adapter position result of {@link #getAdapterPosition()} OR the backup position
 * preset and known, if the previous result was {@link RecyclerView#NO_POSITION}.
 * @see #setBackupPosition(int)
 * @since 5.0.0-b6
 */
public final int getFlexibleAdapterPosition() {
    int position = getAdapterPosition();
    if (position == RecyclerView.NO_POSITION) {
        position = mBackupPosition;
    }
    return position;
}