android.support.v7.widget.RecyclerView.LayoutManager#getChildCount ( )源码实例Demo

private List<ViewHolder> findSwapTargets(ViewHolder viewHolder) {
    if (this.mSwapTargets == null) {
        this.mSwapTargets = new ArrayList();
        this.mDistances = new ArrayList();
    } else {
        this.mSwapTargets.clear();
        this.mDistances.clear();
    }
    int margin = this.mCallback.getBoundingBoxMargin();
    int left = Math.round(this.mSelectedStartX + this.mDx) - margin;
    int top = Math.round(this.mSelectedStartY + this.mDy) - margin;
    int right = (viewHolder.itemView.getWidth() + left) + (margin * 2);
    int bottom = (viewHolder.itemView.getHeight() + top) + (margin * 2);
    int centerX = (left + right) / 2;
    int centerY = (top + bottom) / 2;
    LayoutManager lm = this.mRecyclerView.getLayoutManager();
    int childCount = lm.getChildCount();
    for (int i = 0; i < childCount; i++) {
        View other = lm.getChildAt(i);
        if (other != viewHolder.itemView && other.getBottom() >= top && other.getTop() <= bottom && other.getRight() >= left && other.getLeft() <= right) {
            ViewHolder otherVh = this.mRecyclerView.getChildViewHolder(other);
            if (this.mCallback.canDropOver(this.mRecyclerView, this.mSelected, otherVh)) {
                int dx = Math.abs(centerX - ((other.getLeft() + other.getRight()) / 2));
                int dy = Math.abs(centerY - ((other.getTop() + other.getBottom()) / 2));
                int dist = (dx * dx) + (dy * dy);
                int pos = 0;
                int cnt = this.mSwapTargets.size();
                int j = 0;
                while (j < cnt && dist > ((Integer) this.mDistances.get(j)).intValue()) {
                    pos++;
                    j++;
                }
                this.mSwapTargets.add(pos, otherVh);
                this.mDistances.add(pos, Integer.valueOf(dist));
            }
        }
    }
    return this.mSwapTargets;
}
 

static int computeScrollOffset(State state, OrientationHelper orientation, View startChild, View endChild, LayoutManager lm, boolean smoothScrollbarEnabled, boolean reverseLayout) {
    if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null || endChild == null) {
        return 0;
    }
    int itemsBefore = reverseLayout ? Math.max(0, (state.getItemCount() - Math.max(lm.getPosition(startChild), lm.getPosition(endChild))) - 1) : Math.max(0, Math.min(lm.getPosition(startChild), lm.getPosition(endChild)));
    if (!smoothScrollbarEnabled) {
        return itemsBefore;
    }
    return Math.round((((float) itemsBefore) * (((float) Math.abs(orientation.getDecoratedEnd(endChild) - orientation.getDecoratedStart(startChild))) / ((float) (Math.abs(lm.getPosition(startChild) - lm.getPosition(endChild)) + 1)))) + ((float) (orientation.getStartAfterPadding() - orientation.getDecoratedStart(startChild))));
}
 

static int computeScrollExtent(State state, OrientationHelper orientation, View startChild, View endChild, LayoutManager lm, boolean smoothScrollbarEnabled) {
    if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null || endChild == null) {
        return 0;
    }
    if (!smoothScrollbarEnabled) {
        return Math.abs(lm.getPosition(startChild) - lm.getPosition(endChild)) + 1;
    }
    return Math.min(orientation.getTotalSpace(), orientation.getDecoratedEnd(endChild) - orientation.getDecoratedStart(startChild));
}
 

static int computeScrollRange(State state, OrientationHelper orientation, View startChild, View endChild, LayoutManager lm, boolean smoothScrollbarEnabled) {
    if (lm.getChildCount() == 0 || state.getItemCount() == 0 || startChild == null || endChild == null) {
        return 0;
    }
    if (!smoothScrollbarEnabled) {
        return state.getItemCount();
    }
    return (int) ((((float) (orientation.getDecoratedEnd(endChild) - orientation.getDecoratedStart(startChild))) / ((float) (Math.abs(lm.getPosition(startChild) - lm.getPosition(endChild)) + 1))) * ((float) state.getItemCount()));
}