SliverWithPinnedFooter

lib/src/rendering/sliver_with_pinned_footer.dart

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+import 'dart:math';
+
+import 'package:flutter/rendering.dart';
+
+class RenderSliverWithPinnedFooterParentData extends ParentData
+    with ContainerParentDataMixin<RenderObject> {}
+
+class RenderSliverWithPinnedFooter extends RenderSliver
+    with
+        ContainerRenderObjectMixin<RenderObject,
+            RenderSliverWithPinnedFooterParentData> {
+  @override
+  void setupParentData(covariant RenderObject child) {
+    if (child.parentData is! RenderSliverWithPinnedFooterParentData) {
+      child.parentData = RenderSliverWithPinnedFooterParentData();
+    }
+  }
+
+  @override
+  void applyPaintTransform(covariant RenderObject child, Matrix4 transform) {
+    if (child == lastChild) {
+      final geometry = this.geometry!;
+      final footer = child as RenderBox;
+      final footerTop =
+          geometry.paintOrigin + geometry.paintExtent - footer.size.height;
+      transform.translate(0.0, footerTop);
+    }
+  }
+
+  @override
+  void performLayout() {
+    final sliver = firstChild as RenderSliver;
+    final footer = lastChild as RenderBox;
+    sliver.layout(constraints, parentUsesSize: true);
+    footer.layout(constraints.asBoxConstraints(), parentUsesSize: true);
+    final paintExtent = min(constraints.remainingPaintExtent,
+        sliver.geometry!.paintExtent + footer.size.height);
+    final layoutExtent = min(constraints.remainingPaintExtent,
+        sliver.geometry!.layoutExtent + footer.size.height);
+    final cacheExtent = min(constraints.remainingPaintExtent,
+        sliver.geometry!.cacheExtent + footer.size.height);
+    geometry = SliverGeometry(
+      scrollExtent: sliver.geometry!.scrollExtent + footer.size.height,
+      paintExtent: paintExtent,
+      paintOrigin: sliver.geometry!.paintOrigin,
+      layoutExtent: layoutExtent,
+      maxPaintExtent: sliver.geometry!.maxPaintExtent + footer.size.height,
+      maxScrollObstructionExtent: sliver.geometry!.maxScrollObstructionExtent,
+      hitTestExtent: paintExtent,
+      visible: sliver.geometry!.visible,
+      hasVisualOverflow: sliver.geometry!.hasVisualOverflow,
+      scrollOffsetCorrection: sliver.geometry!.scrollOffsetCorrection,
+      cacheExtent: cacheExtent,
+    );
+  }
+
+  @override
+  bool hitTestChildren(
+    SliverHitTestResult result, {
+    double? mainAxisPosition,
+    double? crossAxisPosition,
+  }) {
+    if (mainAxisPosition == null || crossAxisPosition == null) return false;
+
+    final geometry = this.geometry!;
+    final sliver = firstChild as RenderSliver;
+    final footer = lastChild as RenderBox;
+    final footerTop =
+        geometry.paintOrigin + geometry.paintExtent - footer.size.height;
+    if (mainAxisPosition >= footerTop) {
+      final hit = footer.hitTest(
+        BoxHitTestResult.wrap(result),
+        position: Offset(crossAxisPosition, mainAxisPosition - footerTop),
+      );
+      if (hit) {
+        return true;
+      }
+    }
+    return sliver.hitTest(
+      result,
+      mainAxisPosition: mainAxisPosition,
+      crossAxisPosition: crossAxisPosition,
+    );
+  }
+
+  @override
+  void paint(PaintingContext context, Offset offset) {
+    final geometry = this.geometry!;
+    final sliver = firstChild as RenderSliver;
+    final footer = lastChild as RenderBox;
+    context.paintChild(sliver, offset);
+    context.paintChild(
+      footer,
+      Offset(
+        offset.dx,
+        offset.dy +
+            geometry.paintOrigin +
+            geometry.paintExtent -
+            footer.size.height,
+      ),
+    );
+  }
+}

lib/src/sliver_with_pinned_footer.dart

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+import 'package:flutter/widgets.dart';
+
+import 'rendering/sliver_with_pinned_footer.dart';
+
+/// [SliverWithPinnedFooter] adds the ability to have a pinned footer at the bottom of a sliver.
+///
+/// The sliver will be layed out first and the footer will be added below if there
+/// is enough room left in the viewport. If there is not enough room then the footer
+/// will be painted on top of the sliver at the bottom of the painted area of the sliver.
+///
+/// The total size of this sliver will be the paintExtent of the passed in sliver
+/// plus the height of the footer.
+class SliverWithPinnedFooter extends MultiChildRenderObjectWidget {
+  SliverWithPinnedFooter({
+    Key? key,
+    required Widget sliver,
+    required Widget footer,
+  }) : super(key: key, children: [sliver, footer]);
+
+  @override
+  RenderObject createRenderObject(BuildContext context) {
+    return RenderSliverWithPinnedFooter();
+  }
+}