ListViewRendererHackfix_AutomaticHeaderHeights_20190418.cs

    // Fixes broken ListView header heights on iOS
    public sealed class ListViewRendererHackfix_AutomaticHeaderHeights_20190418 : ListViewRenderer {
        private static readonly FieldInfo fieldInfo_ListViewRenderer_dataSource = typeof(ListViewRenderer).GetField("_dataSource", BindingFlags.Instance | BindingFlags.NonPublic);
        private static readonly Type type_ListViewRenderer_ListViewDataSource = typeof(ListViewRenderer).GetNestedType("ListViewDataSource", BindingFlags.NonPublic);
        private static readonly Type type_ListViewRenderer_UnevenListViewDataSource = typeof(ListViewRenderer).GetNestedType("UnevenListViewDataSource", BindingFlags.NonPublic);
        private static readonly ConstructorInfo ctorInfo_ListViewRenderer_ListViewDataSource = type_ListViewRenderer_ListViewDataSource.GetConstructor(new[] { fieldInfo_ListViewRenderer_dataSource.FieldType });
        private static readonly ConstructorInfo ctorInfo_ListViewRenderer_UnevenListViewDataSource = type_ListViewRenderer_UnevenListViewDataSource.GetConstructor(new[] { fieldInfo_ListViewRenderer_dataSource.FieldType });

        protected override void OnElementChanged(ElementChangedEventArgs<ListView> e) {
            base.OnElementChanged(e);

            if (e.NewElement != null) {
                Control.Source = new CustomListViewDataSource(Control.Source);
            }

            if (Control != null) {
                // Somewhat optional - not core to the fix.
                Control.RowHeight = UITableView.AutomaticDimension;
                Control.EstimatedRowHeight = 40;
                Control.SectionHeaderHeight = UITableView.AutomaticDimension;
                Control.EstimatedSectionHeaderHeight = 40;
                Control.SectionFooterHeight = 0;
                Control.EstimatedSectionFooterHeight = 0;
            }
        }

        protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e) {
            if (e.PropertyName == ListView.HasUnevenRowsProperty.PropertyName) {
                var ctor = Element.HasUnevenRows ? ctorInfo_ListViewRenderer_UnevenListViewDataSource : ctorInfo_ListViewRenderer_ListViewDataSource;
                var dataSource = fieldInfo_ListViewRenderer_dataSource.GetValue(this);
                var tvs = (UITableViewSource)ctor.Invoke(new[] { dataSource });
                fieldInfo_ListViewRenderer_dataSource.SetValue(this, tvs);
                Control.Source = new CustomListViewDataSource(tvs);
                Control.ReloadData();
            } else {
                base.OnElementPropertyChanged(sender, e);
            }
        }

        public sealed class CustomListViewDataSource : UITableViewSource {
            private readonly UITableViewSource inner;
            private readonly MethodInfo methodInfo_DetermineEstimatedRowHeight;
            private PropertyInfo propertyInfo_HeaderWrapperView_Cell;

            public CustomListViewDataSource(UITableViewSource inner) {
                this.inner = inner;
                methodInfo_DetermineEstimatedRowHeight = inner.GetType().BaseType.GetMethod("DetermineEstimatedRowHeight", BindingFlags.Instance | BindingFlags.NonPublic);
            }

            public override nfloat GetHeightForHeader(UITableView tableView, nint section) {
                var r = inner.GetHeightForHeader(tableView, section);
                r = UITableView.AutomaticDimension;
                return r;
            }

            public override UIView GetViewForHeader(UITableView tableView, nint section) {
                var innerWrapper = inner.GetViewForHeader(tableView, section);
                var pi = propertyInfo_HeaderWrapperView_Cell ?? (propertyInfo_HeaderWrapperView_Cell = innerWrapper.GetType().GetProperty("Cell", BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public));
                var cell = (Cell)pi.GetValue(innerWrapper);

                var cellView = innerWrapper.Subviews[0];
                var newWrapper = new HeaderWrapperView(cell, cellView);
                return newWrapper;
            }

            public override void HeaderViewDisplayingEnded(UITableView tableView, UIView headerView, nint section) {
                if (headerView is HeaderWrapperView wrapper) {
                    wrapper.Cell?.SendDisappearing();
                    wrapper.Cell = null;
                }
            }

            public override void WillDisplay(UITableView tableView, UITableViewCell cell, NSIndexPath indexPath) {
                // Newer versions of XamForms override this method in UITableViewSource - so to maintain compat with older and newer, we use conditional reflection to pass-thru this method call.
                if (methodInfo_DetermineEstimatedRowHeight != null)
                    methodInfo_DetermineEstimatedRowHeight.Invoke(inner, new object[0]);
            }

            #region Irrelevant
            public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath) {
                return inner.GetCell(tableView, indexPath);
            }

            public override nint RowsInSection(UITableView tableView, nint section) {
                return inner.RowsInSection(tableView, section);
            }

            public override nfloat GetHeightForRow(UITableView tableView, NSIndexPath indexPath) {
                return inner.GetHeightForRow(tableView, indexPath);
            }

            public override void DraggingEnded(UIScrollView scrollView, bool willDecelerate) {
                inner.DraggingEnded(scrollView, willDecelerate);
            }

            public override void DraggingStarted(UIScrollView scrollView) {
                inner.DraggingStarted(scrollView);
            }

            public override nint NumberOfSections(UITableView tableView) {
                return inner.NumberOfSections(tableView);
            }

            public override void RowDeselected(UITableView tableView, NSIndexPath indexPath) {
                inner.RowDeselected(tableView, indexPath);
            }

            public override void RowSelected(UITableView tableView, NSIndexPath indexPath) {
                inner.RowSelected(tableView, indexPath);
            }

            public override void Scrolled(UIScrollView scrollView) {
                inner.Scrolled(scrollView);
            }

            public override string[] SectionIndexTitles(UITableView tableView) {
                return inner.SectionIndexTitles(tableView);
            }
            #endregion

            protected override void Dispose(bool disposing) {
                inner.Dispose();
            }

            private class HeaderWrapperView : UIView {
                public Cell Cell { get; set; }
                public UIView Subview { get; private set; }

                public HeaderWrapperView(Cell cell, UIView subview) {
                    Cell = cell;
                    Subview = subview;
                    AddSubview(subview);
                }

                public override CGSize SizeThatFits(CGSize size) {
                    return Subview.SizeThatFits(size);
                }

                public override CGSize IntrinsicContentSize => Subview.IntrinsicContentSize;

                public override void LayoutSubviews() {
                    base.LayoutSubviews();
                    Subview.Frame = Bounds;
                }
            }
        }
    }

thank you a lot!