android.support.v7.widget.LinearLayoutManager#findFirstVisibleItemPosition ( )源码实例Demo

下面列出了android.support.v7.widget.LinearLayoutManager#findFirstVisibleItemPosition ( ) 实例代码，或者点击链接到github查看源代码，也可以在右侧发表评论。

源代码1 项目： SnappyRecyclerView 文件： SnappingRecyclerView.java

/**
 * Calculates the distance between the RecyclerView's anchor, either the start, center or end,
 * and the View which is closest to the anchor.
 *
 * @return The distance between RecyclerView anchor and View closest to anchor
 */
private int calculateSnapDistance() {
    LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager();

    int parentAnchor = getParentAnchor(orientation, anchor);

    int lastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition();
    int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();

    View currentViewClosestToAnchor = linearLayoutManager.findViewByPosition(firstVisibleItemPosition);

    int currentViewClosestToAnchorDistance = parentAnchor - getViewAnchor(currentViewClosestToAnchor, orientation, anchor);

    for(int i = firstVisibleItemPosition + 1; i <= lastVisibleItemPosition; i++) {
        View view = linearLayoutManager.findViewByPosition(i);
        int distanceToAnchor = parentAnchor - getViewAnchor(view, orientation, anchor);

        if (Math.abs(distanceToAnchor) < Math.abs(currentViewClosestToAnchorDistance)) {
            currentViewClosestToAnchorDistance = distanceToAnchor;
        }
    }

    return currentViewClosestToAnchorDistance;
}

源代码2 项目： GridPagerSnapHelper 文件： BasePageIndicator.java

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

    onPageScrollStateChanged(newState);

    if (newState == RecyclerView.SCROLL_STATE_IDLE) {
        RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();

        int position = 0;
        if (layoutManager instanceof GridLayoutManager) {
            GridLayoutManager gridLayoutManager = (GridLayoutManager) layoutManager;
            position = gridLayoutManager.findFirstVisibleItemPosition();
            int row = gridLayoutManager.getSpanCount();
            position = position / (row * mPageColumn);
        } else if (layoutManager instanceof LinearLayoutManager) {
            LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
            position = linearLayoutManager.findFirstVisibleItemPosition();
        }

        onPageSelected(position);
    }
}

源代码3 项目： RunMap 文件： V2MainFragment.java

@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
    super.onScrollStateChanged(recyclerView, newState);
    RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
    if (layoutManager instanceof LinearLayoutManager) {
        LinearLayoutManager linearManager = (LinearLayoutManager) layoutManager;
        int firstItemPosition = linearManager.findFirstVisibleItemPosition();
        if(firstItemPosition == 0 || mContentListAdapter.getItemCount() == 0){
            mRefreshLayout.setEnabled(true);
            CFLog.e("V2MainFragment", "arrive top");
        }
        else{
            mRefreshLayout.setEnabled(false);
        }
    }
}

源代码4 项目： AndroidDemo 文件： RecyclerViewScrollActivity.java

private void moveToPosition(int position) {
    if (position > data.size())
        return;
    LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
    int first = layoutManager.findFirstVisibleItemPosition();
    int end = layoutManager.findLastVisibleItemPosition();
    if (first == -1 || end == -1)
        return;
    if (position <= first) {
        layoutManager.scrollToPosition(position);
    } else if (position >= end) {
        isMove = true;
        scrollPosition = position;
        layoutManager.smoothScrollToPosition(recyclerView, null, position);
    } else {//中间部分
        int n = position - layoutManager.findFirstVisibleItemPosition();
        if (n > 0 && n < data.size()) {
            int top = layoutManager.findViewByPosition(position).getTop();
            recyclerView.scrollBy(0, top);
        }
    }
}

源代码5 项目： NIM_Android_UIKit 文件： BaseFetchLoadAdapter.java

public void fetchMoreComplete(int newDataSize) {
    if (getFetchMoreViewCount() == 0) {
        return;
    }

    mFetching = false;
    mFetchMoreView.setLoadMoreStatus(LoadMoreView.STATUS_DEFAULT);
    notifyItemChanged(0);

    // 定位到insert新消息前的top消息位置。必须移动，否则还在顶部，会继续fetch!!!
    if (mRecyclerView != null) {
        RecyclerView.LayoutManager layoutManager = mRecyclerView.getLayoutManager();
        // 只有LinearLayoutManager才有查找第一个和最后一个可见view位置的方法
        if (layoutManager instanceof LinearLayoutManager) {
            LinearLayoutManager linearManager = (LinearLayoutManager) layoutManager;
            //获取第一个可见view的位置
            int firstItemPosition = linearManager.findFirstVisibleItemPosition();
            if (firstItemPosition == 0) {
                // 最顶部可见的View已经是FetchMoreView了，那么add数据&局部刷新后，要进行定位到上次的最顶部消息。
                mRecyclerView.scrollToPosition(newDataSize + getFetchMoreViewCount());
            }
        } else {
            mRecyclerView.scrollToPosition(newDataSize);
        }
    }
}

源代码6 项目： CustomViewSets 文件： SnappyRecyclerView.java

@Override
    public void onScrollStateChanged(int state) {
        super.onScrollStateChanged(state);

        // If you tap on the phone while the RecyclerView is scrolling it will stop in the middle.
        // This code fixes this. This code is not strictly necessary but it improves the behaviour.

        if (state == SCROLL_STATE_IDLE) {
            LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager();

//            int screenWidth = Resources.getSystem().getDisplayMetrics().widthPixels;
            int screenWidth = getMeasuredWidth();
            // views on the screen
            int lastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition();
            View lastView = linearLayoutManager.findViewByPosition(lastVisibleItemPosition);
            int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
            View firstView = linearLayoutManager.findViewByPosition(firstVisibleItemPosition);

            // distance we need to scroll
            int leftMargin = (screenWidth - lastView.getWidth()) / 2;
            int rightMargin = (screenWidth - firstView.getWidth()) / 2 + firstView.getWidth();
            int leftEdge = lastView.getLeft();
            int rightEdge = firstView.getRight();
            int scrollDistanceLeft = leftEdge - leftMargin;
            int scrollDistanceRight = rightMargin - rightEdge;

            if (leftEdge > screenWidth / 2) {
                smoothScrollBy(-scrollDistanceRight, 0);
            } else if (rightEdge < screenWidth / 2) {
                smoothScrollBy(scrollDistanceLeft, 0);
            }
        }
    }

源代码7 项目： andela-med-manager 文件： CirclePagerIndicatorDecoration.java

@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
    super.onDrawOver(c, parent, state);

    int itemCount = parent.getAdapter().getItemCount();

    // center horizontally, calculate width and subtract half from center
    float totalLength = mIndicatorItemLength * itemCount;
    float paddingBetweenItems = Math.max(0, itemCount - 1) * mIndicatorItemPadding;
    float indicatorTotalWidth = totalLength + paddingBetweenItems;
    float indicatorStartX = (parent.getWidth() - indicatorTotalWidth) / 2F;

    // center vertically in the allotted space
    float indicatorPosY = parent.getHeight() - mIndicatorHeight / 2F;

    drawInactiveIndicators(c, indicatorStartX, indicatorPosY, itemCount);

    // find active page (which should be highlighted)
    LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
    int activePosition = layoutManager.findFirstVisibleItemPosition();
    if (activePosition == RecyclerView.NO_POSITION) {
        return;
    }

    // find offset of active page (if the user is scrolling)
    final View activeChild = layoutManager.findViewByPosition(activePosition);
    int left = activeChild.getLeft();
    int width = activeChild.getWidth();

    // on swipe the active item will be positioned from [-width, 0]
    // interpolate offset for smooth animation
    float progress = mInterpolator.getInterpolation(left * -1 / (float) width);

    drawHighlights(c, indicatorStartX, indicatorPosY, activePosition, progress, itemCount);
}

源代码8 项目： VideoOS-Android-SDK 文件： UIRecyclerViewMethodMapper.java

@Override
public Varargs offset(U view, Varargs varargs) {
    if (varargs.narg() > 1) {
        return setScrollXY(view, varargs);
    } else {
        LinearLayoutManager layoutManager = (LinearLayoutManager) view.getLVRecyclerView().getLayoutManager();
        int position = layoutManager.findFirstVisibleItemPosition();
        View firstVisiableChildView = layoutManager.findViewByPosition(position);
        int dy = (position) * firstVisiableChildView.getHeight() - firstVisiableChildView.getTop();
        return varargsOf(valueOf(0), valueOf(DimenUtil.pxToDpi(dy)));
    }
}

源代码9 项目： Conversations 文件： ConversationsOverviewFragment.java

private ScrollState getScrollState() {
	if (this.binding == null) {
		return null;
	}
	LinearLayoutManager layoutManager = (LinearLayoutManager) this.binding.list.getLayoutManager();
	int position = layoutManager.findFirstVisibleItemPosition();
	final View view = this.binding.list.getChildAt(0);
	if (view != null) {
		return new ScrollState(position,view.getTop());
	} else {
		return new ScrollState(position, 0);
	}
}

源代码10 项目： AndroidUI 文件： MainActivity.java

/**
 * 获取当前fragment状态，在Demo中简单演示了RecyclerView的位置恢复
 */
public void getState() {

    RecyclerView recyclerView = mMainFragment.getRecyclerView();
    recyclerView.stopScroll();
    if (recyclerView.getLayoutManager() instanceof LinearLayoutManager){
        LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
        int position = layoutManager.findFirstVisibleItemPosition();
        int scroll = recyclerView.getChildAt(0).getTop();

        addFragment(position,scroll);
    }

}

源代码11 项目： Cinema-App-Concept 文件： LinePagerIndicatorDecoration.java

@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
    super.onDrawOver(c, parent, state);

    int itemCount = parent.getAdapter().getItemCount();

    // center horizontally, calculate width and subtract half from center
    float totalLength = mIndicatorItemLength * itemCount;
    float paddingBetweenItems = Math.max(0, itemCount - 1) * mIndicatorItemPadding;
    float indicatorTotalWidth = totalLength + paddingBetweenItems;
    float indicatorStartX = (parent.getWidth() - indicatorTotalWidth) / 2F;

    // center vertically in the allotted space
    float indicatorPosY = parent.getHeight() - mIndicatorHeight / 2F;

    drawInactiveIndicators(c, indicatorStartX, indicatorPosY, itemCount);


    // find active page (which should be highlighted)
    LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();

    int activePosition = layoutManager.findFirstVisibleItemPosition();
    if (activePosition == RecyclerView.NO_POSITION) {
        return;
    }

    // find offset of active page (if the user is scrolling)
    final View activeChild = layoutManager.findViewByPosition(activePosition);
    int left = activeChild.getLeft();
    int width = activeChild.getWidth();

    // on swipe the active item will be positioned from [-width, 0]
    // interpolate offset for smooth animation
    float progress = mInterpolator.getInterpolation(left * -1 / (float) width);

    drawHighlights(c, indicatorStartX, indicatorPosY, activePosition, progress, itemCount);
}

源代码12 项目： Cinema-App-Concept 文件： CirclePagerIndicatorDecoration.java

@Override
public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
    super.onDrawOver(c, parent, state);

    int itemCount = parent.getAdapter().getItemCount();

    // center horizontally, calculate width and subtract half from center
    float totalLength = mIndicatorItemLength * itemCount;
    float paddingBetweenItems = Math.max(0, itemCount - 1) * mIndicatorItemPadding;
    float indicatorTotalWidth = totalLength + paddingBetweenItems;
    float indicatorStartX = (parent.getWidth() - indicatorTotalWidth) / 2F;

    // center vertically in the allotted space
    float indicatorPosY = parent.getHeight() - mIndicatorHeight / 2F;

    drawInactiveIndicators(c, indicatorStartX, indicatorPosY, itemCount);


    // find active page (which should be highlighted)
    LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
    int activePosition = layoutManager.findFirstVisibleItemPosition();
    if (activePosition == RecyclerView.NO_POSITION) {
        return;
    }

    // find offset of active page (if the user is scrolling)
    final View activeChild = layoutManager.findViewByPosition(activePosition);
    int left = activeChild.getLeft();
    int width = activeChild.getWidth();

    // on swipe the active item will be positioned from [-width, 0]
    // interpolate offset for smooth animation
    float progress = mInterpolator.getInterpolation(left * -1 / (float) width);

    drawHighlights(c, indicatorStartX, indicatorPosY, activePosition, progress, itemCount);
}

源代码13 项目： demo4Fish 文件： HomeViewLayer.java

@Override
public void run() {
    LinearLayoutManager manager = (LinearLayoutManager) mBannerListView.getLayoutManager();
    int position = manager.findFirstVisibleItemPosition();
    mBannerListView.smoothScrollToPosition(position + 1);
    startSlideBanner();
}

源代码14 项目： QuickReturn 文件： QuickReturnUtils.java

public static int getScrollY(RecyclerView rv, int columnCount) {
        View c = rv.getChildAt(0);
        if (c == null) {
            return 0;
        }

        LinearLayoutManager layoutManager = (LinearLayoutManager) rv.getLayoutManager();
        int firstVisiblePosition = layoutManager.findFirstVisibleItemPosition();

//        Log.d("", "getScrollY() : firstVisiblePosition - " + firstVisiblePosition);

        int scrollY = -(c.getTop());

//        Log.d("", "getScrollY() : scrollY - " + scrollY);

        if (columnCount > 1) {
            sRecyclerViewItemHeights.put(firstVisiblePosition, c.getHeight() + QuickReturnUtils.dp2px(rv.getContext(), 8) / columnCount);
        } else {
            sRecyclerViewItemHeights.put(firstVisiblePosition, c.getHeight());
        }

        if (scrollY < 0)
            scrollY = 0;

        for (int i = 0; i < firstVisiblePosition; ++i) {
            if (sRecyclerViewItemHeights.get(i) != null) // (this is a sanity check)
                scrollY += sRecyclerViewItemHeights.get(i); //add all heights of the views that are gone
        }

        return scrollY;
    }

源代码15 项目： FastAndroid 文件： RecyclerToListViewScrollListener.java

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();

    int firstVisible = layoutManager.findFirstVisibleItemPosition();
    int visibleCount = Math.abs(firstVisible - layoutManager.findLastVisibleItemPosition());
    int itemCount = recyclerView.getAdapter().getItemCount();

    if (firstVisible != lastFirstVisible || visibleCount != lastVisibleCount || itemCount != lastItemCount) {
        scrollListener.onScroll(null, firstVisible, visibleCount, itemCount);
        lastFirstVisible = firstVisible;
        lastVisibleCount = visibleCount;
        lastItemCount = itemCount;
    }
}

源代码16 项目： YCScrollPager 文件： ScrollPageHelper.java

@Nullable
private View findEndView(RecyclerView.LayoutManager layoutManager,
                         @NonNull OrientationHelper helper) {

    if (layoutManager instanceof LinearLayoutManager) {
        LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
        boolean reverseLayout = linearLayoutManager.getReverseLayout();
        int lastChild = reverseLayout ? linearLayoutManager.findFirstVisibleItemPosition()
                : linearLayoutManager.findLastVisibleItemPosition();
        int offset = 1;

        if (layoutManager instanceof GridLayoutManager) {
            offset += ((GridLayoutManager) layoutManager).getSpanCount() - 1;
        }

        if (lastChild == RecyclerView.NO_POSITION) {
            return null;
        }

        View child = layoutManager.findViewByPosition(lastChild);

        float visibleWidth;

        if (isRtlHorizontal) {
            visibleWidth = (float) helper.getDecoratedEnd(child)
                    / helper.getDecoratedMeasurement(child);
        } else {
            visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
                    / helper.getDecoratedMeasurement(child);
        }

        boolean startOfList;
        if (!reverseLayout) {
            startOfList = ((LinearLayoutManager) layoutManager)
                    .findFirstCompletelyVisibleItemPosition() == 0;
        } else {
            startOfList = ((LinearLayoutManager) layoutManager)
                    .findLastCompletelyVisibleItemPosition()
                    == layoutManager.getItemCount() - 1;
        }

        if (visibleWidth > 0.5f && !startOfList) {
            return child;
        } else if (snapLastItem && startOfList) {
            return child;
        } else if (startOfList) {
            return null;
        } else {
            return reverseLayout ? layoutManager.findViewByPosition(lastChild + offset)
                    : layoutManager.findViewByPosition(lastChild - offset);
        }
    }
    return null;
}

源代码17 项目： CustomViewSets 文件： SnappyRecyclerView.java

@Override
    public boolean fling(int velocityX, int velocityY) {
        LinearLayoutManager linearLayoutManager = (LinearLayoutManager) getLayoutManager();

//        int screenWidth = Resources.getSystem().getDisplayMetrics().widthPixels;
        int screenWidth = getMeasuredWidth();
        // views on the screen
        int lastVisibleItemPosition = linearLayoutManager.findLastVisibleItemPosition();
        View lastView = linearLayoutManager.findViewByPosition(lastVisibleItemPosition);
        int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
        View firstView = linearLayoutManager.findViewByPosition(firstVisibleItemPosition);

        // distance we need to scroll
        int leftMargin = (screenWidth - lastView.getWidth()) / 2;
        int rightMargin = (screenWidth - firstView.getWidth()) / 2 + firstView.getWidth();
        int leftEdge = lastView.getLeft();
        int rightEdge = firstView.getRight();
        int scrollDistanceLeft = leftEdge - leftMargin;
        int scrollDistanceRight = rightMargin - rightEdge;

        if (Math.abs(velocityX) < 1000) {
            // The fling is slow -> stay at the current page if we are less than half through,
            // or go to the next page if more than half through

            if (leftEdge > screenWidth / 2) {
                // go to next page
                smoothScrollBy(-scrollDistanceRight, 0);
            } else if (rightEdge < screenWidth / 2) {
                // go to next page
                smoothScrollBy(scrollDistanceLeft, 0);
            } else {
                // stay at current page
                if (velocityX > 0) {
                    smoothScrollBy(-scrollDistanceRight, 0);
                } else {
                    smoothScrollBy(scrollDistanceLeft, 0);
                }
            }
            return true;

        } else {
            // The fling is fast -> go to next page

            if (velocityX > 0) {
                smoothScrollBy(scrollDistanceLeft, 0);
            } else {
                smoothScrollBy(-scrollDistanceRight, 0);
            }
            return true;

        }

    }

源代码18 项目： YCRefreshView 文件： ScrollPageHelper.java

@Nullable
private View findEndView(RecyclerView.LayoutManager layoutManager,
                         @NonNull OrientationHelper helper) {

    if (layoutManager instanceof LinearLayoutManager) {
        LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
        boolean reverseLayout = linearLayoutManager.getReverseLayout();
        int lastChild = reverseLayout ? linearLayoutManager.findFirstVisibleItemPosition()
                : linearLayoutManager.findLastVisibleItemPosition();
        int offset = 1;

        if (layoutManager instanceof GridLayoutManager) {
            offset += ((GridLayoutManager) layoutManager).getSpanCount() - 1;
        }

        if (lastChild == RecyclerView.NO_POSITION) {
            return null;
        }

        View child = layoutManager.findViewByPosition(lastChild);

        float visibleWidth;

        if (isRtlHorizontal) {
            visibleWidth = (float) helper.getDecoratedEnd(child)
                    / helper.getDecoratedMeasurement(child);
        } else {
            visibleWidth = (float) (helper.getTotalSpace() - helper.getDecoratedStart(child))
                    / helper.getDecoratedMeasurement(child);
        }

        boolean startOfList;
        if (!reverseLayout) {
            startOfList = ((LinearLayoutManager) layoutManager)
                    .findFirstCompletelyVisibleItemPosition() == 0;
        } else {
            startOfList = ((LinearLayoutManager) layoutManager)
                    .findLastCompletelyVisibleItemPosition()
                    == layoutManager.getItemCount() - 1;
        }

        if (visibleWidth > 0.5f && !startOfList) {
            return child;
        } else if (snapLastItem && startOfList) {
            return child;
        } else if (startOfList) {
            return null;
        } else {
            return reverseLayout ? layoutManager.findViewByPosition(lastChild + offset)
                    : layoutManager.findViewByPosition(lastChild - offset);
        }
    }
    return null;
}

源代码19 项目： ucar-weex-core 文件： WXRecyclerViewOnScrollListener.java

@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");
    }
  }
}

源代码20 项目： IndexableRecyclerView 文件： IndexableLayout.java

private void processScrollListener() {
    if (!(mLayoutManager instanceof LinearLayoutManager)) return;

    LinearLayoutManager linearLayoutManager = (LinearLayoutManager) mLayoutManager;

    int firstItemPosition;
    firstItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
    if (firstItemPosition == RecyclerView.NO_POSITION) return;

    mIndexBar.setSelection(firstItemPosition);

    if (!mSticyEnable) return;
    ArrayList<EntityWrapper> list = mRealAdapter.getItems();
    if (mStickyViewHolder != null && list.size() > firstItemPosition) {
        EntityWrapper wrapper = list.get(firstItemPosition);
        String wrapperTitle = wrapper.getIndexTitle();

        if (EntityWrapper.TYPE_TITLE == wrapper.getItemType()) {
            if (mLastInvisibleRecyclerViewItemView != null && mLastInvisibleRecyclerViewItemView.getVisibility() == INVISIBLE) {
                mLastInvisibleRecyclerViewItemView.setVisibility(VISIBLE);
                mLastInvisibleRecyclerViewItemView = null;
            }

            mLastInvisibleRecyclerViewItemView = linearLayoutManager.findViewByPosition(firstItemPosition);

            if (mLastInvisibleRecyclerViewItemView != null) {
                mLastInvisibleRecyclerViewItemView.setVisibility(INVISIBLE);
            }
        }

        // hide -> show
        if (wrapperTitle == null && mStickyViewHolder.itemView.getVisibility() == VISIBLE) {
            mStickyTitle = null;
            mStickyViewHolder.itemView.setVisibility(INVISIBLE);
        } else {
            stickyNewViewHolder(wrapperTitle);
        }

        // GirdLayoutManager
        if (mLayoutManager instanceof GridLayoutManager) {
            GridLayoutManager gridLayoutManager = (GridLayoutManager) mLayoutManager;
            if (firstItemPosition + gridLayoutManager.getSpanCount() < list.size()) {
                for (int i = firstItemPosition + 1; i <= firstItemPosition + gridLayoutManager.getSpanCount(); i++) {
                    processScroll(linearLayoutManager, list, i, wrapperTitle);
                }
            }
        } else {   // LinearLayoutManager
            if (firstItemPosition + 1 < list.size()) {
                processScroll(linearLayoutManager, list, firstItemPosition + 1, wrapperTitle);
            }
        }
    }
}

方法所在类

android.support.v7.widget.LinearLayoutManager