From f1a318b7f39263d31e6c80b465597871b7e9810a Mon Sep 17 00:00:00 2001
From: mmucaria <mmucaria@technogym.com>
Date: Thu, 1 Dec 2022 09:49:30 +0100
Subject: [PATCH] adds the possibility to nest multiple sticky headers

---
 lib/sticky_headers/render.dart | 13 ++++++++++++-
 lib/sticky_headers/widget.dart |  4 ++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/lib/sticky_headers/render.dart b/lib/sticky_headers/render.dart
index f83e58f..997fb10 100644
--- a/lib/sticky_headers/render.dart
+++ b/lib/sticky_headers/render.dart
@@ -27,6 +27,7 @@ class RenderStickyHeader extends RenderBox
   RenderStickyHeaderCallback? _callback;
   ScrollPosition _scrollPosition;
   bool _overlapHeaders;
+  double _offset;
 
   RenderStickyHeader({
     required ScrollPosition scrollPosition,
@@ -34,8 +35,10 @@ class RenderStickyHeader extends RenderBox
     bool overlapHeaders = false,
     RenderBox? header,
     RenderBox? content,
+    double? offset,
   })  : _scrollPosition = scrollPosition,
         _callback = callback,
+        _offset = offset ?? 0,
         _overlapHeaders = overlapHeaders {
     if (content != null) add(content);
     if (header != null) add(header);
@@ -62,6 +65,14 @@ class RenderStickyHeader extends RenderBox
     markNeedsLayout();
   }
 
+  set offset(double newValue) {
+    if (_offset == newValue) {
+      return;
+    }
+    _offset = newValue;
+    markNeedsLayout();
+  }
+
   set overlapHeaders(bool newValue) {
     if (_overlapHeaders == newValue) {
       return;
@@ -135,7 +146,7 @@ class RenderStickyHeader extends RenderBox
     final scrollBox = _scrollPosition.context.notificationContext!.findRenderObject();
     if (scrollBox?.attached ?? false) {
       try {
-        return localToGlobal(Offset.zero, ancestor: scrollBox).dy;
+        return localToGlobal(Offset.zero, ancestor: scrollBox).dy - _offset;
       } catch (e) {
         // ignore and fall-through and return 0.0
       }
diff --git a/lib/sticky_headers/widget.dart b/lib/sticky_headers/widget.dart
index ca639ef..0e08724 100644
--- a/lib/sticky_headers/widget.dart
+++ b/lib/sticky_headers/widget.dart
@@ -70,10 +70,14 @@ class StickyHeader extends MultiChildRenderObjectWidget {
 
   @override
   void updateRenderObject(BuildContext context, RenderStickyHeader renderObject) {
+    // If we find a parent StickyHeader we look for its size to provide an offset
+    // to current StickyHeader
+    final parent = context.findAncestorRenderObjectOfType<RenderStickyHeader>();
     final scrollPosition = controller?.position ?? Scrollable.of(context)!.position;
     renderObject
       ..scrollPosition = scrollPosition
       ..callback = callback
+      ..offset = parent?.lastChild?.size.height ?? 0
       ..overlapHeaders = overlapHeaders;
   }
 }