Java LayoutManager.getItemCount方法代码示例

import android.support.v7.widget.RecyclerView.LayoutManager; //导入方法依赖的package包/类
/**
 * Searches for the first visible item in the adapter.
 * Checks if it is visible enough (more than half) and returns the view.
 * If the view was not visible enough it will return the next view in line.
 *
 * If we are at the end of the list we return null so no snapping occurs
 *
 * @param layoutManager
 * @param orientationHelper
 * @return the view to snap to
 */
@Nullable
private View findStartView(final LayoutManager layoutManager, final OrientationHelper orientationHelper) {
    View targetView = null;
    if (layoutManager instanceof LinearLayoutManager) {
        final int firstChildPos = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
        if (firstChildPos != RecyclerView.NO_POSITION) {
            final View firstView = layoutManager.findViewByPosition(firstChildPos);
            float visibleWidth = (float) orientationHelper.getDecoratedEnd(firstView) / orientationHelper.getDecoratedMeasurement(firstView);

            if (visibleWidth > VIEW_HALF_VISIBLE) {
                targetView = firstView;
            } else {
                // If we're at the end of the list, we shouldn't snap
                // to avoid having the last item not completely visible.
                boolean endOfList = ((LinearLayoutManager) layoutManager).findLastCompletelyVisibleItemPosition() == layoutManager.getItemCount() - 1;
                if (!endOfList) {
                    // If the firstView wasn't returned, we need to return
                    // the next view closest to the start.
                    targetView = layoutManager.findViewByPosition(firstChildPos + 1);
                }
            }
        }
    }
    return targetView;
}
 

import android.support.v7.widget.RecyclerView.LayoutManager; //导入方法依赖的package包/类
private int getEdge(int position, LayoutManager layoutManager) {
    int edge = 0;
    if (layoutManager instanceof GridLayoutManager) {
        return getEdge(((GridLayoutManager) layoutManager).getSpanCount(), position,
                layoutManager.getItemCount(), ((GridLayoutManager) layoutManager).getOrientation());
    } else if (layoutManager instanceof LinearLayoutManager) {
        if (((LinearLayoutManager) layoutManager).getOrientation() == LinearLayoutManager.VERTICAL) {
            edge |= EDGE_LEFT;
            edge |= EDGE_RIGHT;
            if (position == 0) {
                edge |= EDGE_TOP;
            }
            if (position == layoutManager.getItemCount() - 1) {
                edge |= EDGE_BOTTOM;
            }
        } else {
            edge |= EDGE_TOP;
            edge |= EDGE_BOTTOM;
            if (position == 0) {
                edge |= EDGE_LEFT;
            }
            if (position == layoutManager.getItemCount() - 1) {
                edge |= EDGE_RIGHT;
            }
        }
    } else if (layoutManager instanceof StaggeredGridLayoutManager) {
        //瀑布布局,分割线不好加
    }

    return edge;
}
 

import android.support.v7.widget.RecyclerView.LayoutManager; //导入方法依赖的package包/类
@Override
public void onScrolled(@NonNull final RecyclerView view, final int dx, final int dy) {
    // short-circuit if we are currently loading more data
    if (mLoading) {
        return;
    }

    // short-circuit if there isn't a valid layout manager
    final LayoutManager layoutManager = view.getLayoutManager();
    if (layoutManager == null) {
        return;
    }

    // determine the last visible item
    final int lastVisible;
    if (layoutManager instanceof LinearLayoutManager) {
        lastVisible = ((LinearLayoutManager) layoutManager).findLastVisibleItemPosition();
    } else {
        lastVisible = getLastVisiblePosition(layoutManager);
    }

    // have we passed the threshold to load more data?
    if (lastVisible + mThreshold > layoutManager.getItemCount() - 1) {
        mLoading = true;
        onLoadMore();
    }
}
 

import android.support.v7.widget.RecyclerView.LayoutManager; //导入方法依赖的package包/类
/***
 * Well composition does not work so we copy this method from {@link LinearSnapHelper}.
 * That sucks!
 *
 * @param layoutManager
 * @param velocityX
 * @param velocityY
 * @return
 */
@Override
public int findTargetSnapPosition(final LayoutManager layoutManager, final int velocityX, final int velocityY) {
    if (!(layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) {
        return RecyclerView.NO_POSITION;
    }

    final int itemCount = layoutManager.getItemCount();
    if (itemCount == 0) {
        return RecyclerView.NO_POSITION;
    }

    final View currentView = findSnapView(layoutManager);
    if (currentView == null) {
        return RecyclerView.NO_POSITION;
    }

    final int currentPosition = layoutManager.getPosition(currentView);
    if (currentPosition == RecyclerView.NO_POSITION) {
        return RecyclerView.NO_POSITION;
    }

    RecyclerView.SmoothScroller.ScrollVectorProvider vectorProvider =
            (RecyclerView.SmoothScroller.ScrollVectorProvider) layoutManager;
    // deltaJumps sign comes from the velocity which may not match the order of children in
    // the LayoutManager. To overcome this, we ask for a vector from the LayoutManager to
    // get the direction.
    PointF vectorForEnd = vectorProvider.computeScrollVectorForPosition(itemCount - 1);
    if (vectorForEnd == null) {
        // cannot get a vector for the given position.
        return RecyclerView.NO_POSITION;
    }

    int vDeltaJump, hDeltaJump;
    if (layoutManager.canScrollHorizontally()) {
        hDeltaJump = estimateNextPositionDiffForFling(layoutManager,
                getHorizontalHelper(layoutManager), velocityX, 0);
        if (vectorForEnd.x < 0) {
            hDeltaJump = -hDeltaJump;
        }
    } else {
        hDeltaJump = 0;
    }
    if (layoutManager.canScrollVertically()) {
        vDeltaJump = estimateNextPositionDiffForFling(layoutManager,
                getVerticalHelper(layoutManager), 0, velocityY);
        if (vectorForEnd.y < 0) {
            vDeltaJump = -vDeltaJump;
        }
    } else {
        vDeltaJump = 0;
    }

    int deltaJump = layoutManager.canScrollVertically() ? vDeltaJump : hDeltaJump;
    if (deltaJump == 0) {
        return RecyclerView.NO_POSITION;
    }

    int targetPos = currentPosition + deltaJump;
    if (targetPos < 0) {
        targetPos = 0;
    }
    if (targetPos >= itemCount) {
        targetPos = itemCount - 1;
    }
    return targetPos;
}