ViewPager2

ViewPager2.kt

    /**
     * A lot of places in code rely on an assumption that the page fills the whole ViewPager2.
     *
     * TODO(b/70666617) Allow page width different than width/height 100%/100%
     */
    private RecyclerView.OnChildAttachStateChangeListener enforceChildFillListener() {
        return new RecyclerView.OnChildAttachStateChangeListener() {
            @Override
            public void onChildViewAttachedToWindow(@NonNull View view) {
                RecyclerView.LayoutParams layoutParams =
                        (RecyclerView.LayoutParams) view.getLayoutParams();
                if (layoutParams.width != LayoutParams.MATCH_PARENT
                        || layoutParams.height != LayoutParams.MATCH_PARENT) {
                    throw new IllegalStateException(
                            "Pages must fill the whole ViewPager2 (use match_parent)");
                }
            }

            @Override
            public void onChildViewDetachedFromWindow(@NonNull View view) {
                // nothing
            }
        };
    }