HeaderElevationController.java 文件源码

HeaderElevationController(View header) {
    mHeader = header;
    final Resources res = mHeader.getContext().getResources();
    mMaxElevation = res.getDimension(R.dimen.all_apps_header_max_elevation);
    mScrollToElevation = res.getDimension(R.dimen.all_apps_header_scroll_to_elevation);

    // We need to provide a custom outline so the shadow only appears on the bottom edge.
    // The top, left and right edges are all extended out, and the shadow is clipped
    // by the parent.
    final ViewOutlineProvider vop = new ViewOutlineProvider() {
        @Override
        public void getOutline(View view, Outline outline) {
            final View parent = (View) mHeader.getParent();

            final int left = parent.getLeft(); // Use the parent to account for offsets
            final int top = view.getTop();
            final int right = left + view.getWidth();
            final int bottom = view.getBottom();

            final int offset = Utilities.pxFromDp(mMaxElevation, res.getDisplayMetrics());
            outline.setRect(left - offset, top - offset, right + offset, bottom);
        }
    };
    mHeader.setOutlineProvider(vop);
}