Added sticky bottom scroll helper for expanding content in lists.

Author: 23rd

ui/widgets/scroll_area.h

@@ -253,4 +253,18 @@ class ScrollArea : public RpWidgetBase<QScrollArea> {
 
 };
 
+template <typename Scroll>
+void SetStickyBottomScroll(
+		not_null<Scroll*> scroll,
+		not_null<RpWidget*> inner) {
+	inner->heightValue(
+	) | rpl::combine_previous(
+	) | rpl::on_next([=](int previous, int height) {
+		if (scroll->scrollTop() + scroll->scrollHeight() >= previous) {
+			const auto visible = scroll->scrollHeight();
+			scroll->scrollToY(height - visible, height);
+		}
+	}, inner->lifetime());
+}
+
 } // namespace Ui