public HeaderItemDecoration(RecyclerView.LayoutManager layoutManager, int height) {
if (layoutManager.getClass() == LinearLayoutManager.class) {
mNumberOfChildren = 1;
} else if (layoutManager.getClass() == GridLayoutManager.class) {
mNumberOfChildren = ((GridLayoutManager) layoutManager).getSpanCount();
} else if (layoutManager instanceof StaggeredGridLayoutManager) {
mNumberOfChildren = ((StaggeredGridLayoutManager) layoutManager).getSpanCount();
}
mHeaderHeight = height;
}
private void validateRecycler(RecyclerView recycler, boolean headerAlreadyAligned) {
RecyclerView.LayoutManager layoutManager = recycler.getLayoutManager();
if (layoutManager == null) {
throw new IllegalStateException(
"Be sure to call RecyclerViewHeader constructor after setting your RecyclerView's LayoutManager.");
} else if (layoutManager.getClass()
!= LinearLayoutManager.class // not using instanceof on purpose
&& layoutManager.getClass() != GridLayoutManager.class
&& !(layoutManager instanceof StaggeredGridLayoutManager)) {
throw new IllegalArgumentException(
"Currently RecyclerViewHeader supports only LinearLayoutManager, GridLayoutManager and StaggeredGridLayoutManager.");
}
if (layoutManager instanceof LinearLayoutManager) {
if (((LinearLayoutManager) layoutManager).getOrientation() != LinearLayoutManager.VERTICAL) {
throw new IllegalArgumentException(
"Currently RecyclerViewHeader supports only VERTICAL orientation LayoutManagers.");
}
} else if (layoutManager instanceof StaggeredGridLayoutManager) {
if (((StaggeredGridLayoutManager) layoutManager).getOrientation()
!= StaggeredGridLayoutManager.VERTICAL) {
throw new IllegalArgumentException(
"Currently RecyclerViewHeader supports only VERTICAL orientation StaggeredGridLayoutManagers.");
}
}
if (!headerAlreadyAligned) {
ViewParent parent = recycler.getParent();
if (parent != null
&& !(parent instanceof LinearLayout)
&& !(parent instanceof FrameLayout)
&& !(parent instanceof RelativeLayout)) {
throw new IllegalStateException(
"Currently, NOT already aligned RecyclerViewHeader "
+ "can only be used for RecyclerView with a parent of one of types: LinearLayout, FrameLayout, RelativeLayout.");
}
}
}