Xamarin sample of collapsable sections using MvvmCross

CollapsableSectionTableViewSource.cs

using System;
using MonoTouch.UIKit;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using MonoTouch.Foundation;
using Cirrious.MvvmCross.Binding.ExtensionMethods;

namespace TwinCoders.MvvmCross.TouchUtils.TableViews
{
    public class CollapsableSectionTableViewSource : MultiSectionTableViewSource
    {
        public abstract class CollapsableHeader: UIView
        {
            public abstract event EventHandler TouchUpInside;
        }

        public override IEnumerable ItemsSource
        {
            get { return base.ItemsSource; }
            set
            {
                if (CollapseSectionsByDefault && value != null)
                    _collapsedSections = value.Cast<object>().ToList();

                base.ItemsSource = value;
            }
        }

        public bool CollapseSectionsByDefault { get; set; }

        public delegate CollapsableHeader CreateHeaderDelegate(UITableView tableView, object sectionElement, int sectionIndex, bool collapsed);

        public CreateHeaderDelegate CreateHeader { get; set; }

        private IList _collapsedSections = new List<object>();

        public CollapsableSectionTableViewSource(UITableView tableView, NSString cellIdentifier) : base(tableView, cellIdentifier)
        {
        }

        public override UIView GetViewForHeader(UITableView tableView, int section)
        {
            if (CreateHeader == null)
                return null;

            var sectionElement = ItemsSource.ElementAt(section);
            var isCollapsed = _collapsedSections.Contains(sectionElement);
            var header = CreateHeader(tableView, sectionElement, section, isCollapsed);
            header.TouchUpInside += (sender, args) => ToggleCollapseSection(section);

            return header;
        }

        public override int RowsInSection(UITableView tableview, int section)
        {
            var rows = base.RowsInSection(tableview, section);

            var sectionElement = ItemsSource.ElementAt(section);
            if (_collapsedSections.Contains(sectionElement))
                rows = 0;

            return rows;
        }

        public void SetSectionCollapsed(int section, bool collapsed, bool animated = true) {
            var sectionElement = ItemsSource.ElementAt(section);
            if (sectionElement == null)
                return;

            if (collapsed)
                _collapsedSections.Add(sectionElement);
            else
                _collapsedSections.Remove(sectionElement);


            if (UseAnimations && animated)
                TableView.ReloadSections(new NSIndexSet((uint)section), UITableViewRowAnimation.Automatic);
            else
                ReloadTableData();
        }

        public void ToggleCollapseSection(int section) {
            var sectionElement = ItemsSource.ElementAt(section);
            if (sectionElement == null)
                return;

            var isCollapsed = _collapsedSections.Contains(sectionElement);
            SetSectionCollapsed(section, !isCollapsed);
        }
    }
}

GenericMvxTableViewSource.cs

using System;
using Cirrious.MvvmCross.Binding.Touch.Views;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
using System.Linq;

namespace TwinCoders.MvvmCross.TouchUtils.TableViews
{

    public class GenericMvxTableViewSource : MvxTableViewSource, ITableViewEventSource
    {
        public delegate MvxTableViewCell CreateCellDelegate(UITableView tableView, NSIndexPath indexPath, object item);
        public delegate void CellModifierDelegate(UITableViewCell cell, NSIndexPath indexPath, object item);

        protected virtual NSString CellIdentifier { get; private set; }
        public CreateCellDelegate CreateCell { get; set; }
        public CellModifierDelegate CellModifier { get; set; }

        public GenericMvxTableViewSource(UITableView tableView, NSString cellIdentifier) : base(tableView)
        {
            CellIdentifier = cellIdentifier;
        }

        protected override UITableViewCell GetOrCreateCellFor(UITableView tableView, NSIndexPath indexPath, object item)
        {
            var reuse = tableView.DequeueReusableCell(CellIdentifier);
            var cell = reuse ?? CreateDefaultBindableCell(tableView, indexPath, item);
            if (CellModifier != null)
                CellModifier(cell, indexPath, item);
            return cell;
        }

        protected virtual MvxTableViewCell CreateDefaultBindableCell(UITableView tableView, NSIndexPath indexPath, object item)
        {
            return CreateCell != null ? CreateCell(tableView, indexPath, item) : null;
        }

        public new object SelectedItem { 
            get { return base.SelectedItem; }
            set
            {
                base.SelectedItem = value;

                if (value != null)
                {
                    var index = IndexForElement(value);
                    if (index != null)
                        TableView.SelectRow(index, false, UITableViewScrollPosition.None);
                }
                else
                {
                    var index = TableView.IndexPathForSelectedRow;
                    if (index != null && index.Row >= 0)
                        TableView.DeselectRow(index, false);
                }
            }
        }

        public virtual NSIndexPath IndexForElement(object element) {
            if (ItemsSource == null || element == null)
                return null;

            return NSIndexPath.FromRowSection(ItemsSource.Cast<object>().ToList().IndexOf(element), 0);
        }

        #region ITableViewEventSource implementation

        public event EventHandler OnDecelerationEnded;
        public event EventHandler OnDecelerationStarted;
        public event EventHandler OnDidZoom;
        public event EventHandler OnDraggingStarted;
        public event EventHandler OnScrollAnimationEnded;
        public event EventHandler OnScrolled;
        public event EventHandler OnScrolledToTop;

        public override void DecelerationEnded(UIScrollView scrollView)
        {
            if (OnDecelerationEnded != null)
                OnDecelerationEnded(scrollView, null);
        }
        public override void DecelerationStarted(UIScrollView scrollView)
        {
            if (OnDecelerationStarted != null)
                OnDecelerationStarted(scrollView, null);
        }
        public override void DidZoom(UIScrollView scrollView)
        {
            if (OnDidZoom != null)
                OnDidZoom(scrollView, null);
        }
        public override void DraggingStarted(UIScrollView scrollView)
        {
            if (OnDraggingStarted != null)
                OnDraggingStarted(scrollView, null);
        }
        public override void ScrollAnimationEnded(UIScrollView scrollView)
        {
            if (OnScrollAnimationEnded != null)
                OnScrollAnimationEnded(scrollView, null);
        }
        public override void Scrolled(UIScrollView scrollView)
        {
            if (OnScrolled != null)
                OnScrolled(scrollView, null);
        }
        public override void ScrolledToTop(UIScrollView scrollView)
        {
            if (OnScrolledToTop != null)
                OnScrolledToTop(scrollView, null);
        }

        #endregion

    }
}

MultiSectionTableViewSource.cs

using System;
using Cirrious.MvvmCross.Binding.Touch.Views;
using MonoTouch.Foundation;
using MonoTouch.UIKit;
using System.Collections.Generic;
using System.Collections;
using Cirrious.MvvmCross.Binding.ExtensionMethods;
using System.Linq;

namespace TwinCoders.MvvmCross.TouchUtils.TableViews
{
    public class MultiSectionTableViewSource : GenericMvxTableViewSource
    {
        public delegate IList GetElementsFromSectionDelegate(object section);
        public delegate UIView HeaderDelegate(UITableView tableView, int section, object sectionItem);

        public GetElementsFromSectionDelegate GetElementsFromSection { get; set; }

        public HeaderDelegate CreateHeader { get; set; }
        public HeaderDelegate CreateFooter { get; set; }

        public MultiSectionTableViewSource(UITableView tableView, NSString cellIdentifier) : base(tableView, cellIdentifier)
        {
        }

        protected IList GetElements(object section)
        {
            var elements = section as IList;

            if (GetElementsFromSection != null)
                elements = GetElementsFromSection(section);

            return elements;
        } 

        protected override object GetItemAt(NSIndexPath indexPath)
        {
            return ItemsSource == null ? null : GetElements(ItemsSource.ElementAt(indexPath.Section)).ElementAt(indexPath.Row);
        }

        public override int NumberOfSections(UITableView tableView)
        {
            return ItemsSource == null ? 0 : ItemsSource.Count();
        }

        public override int RowsInSection(UITableView tableview, int section)
        {
            return ItemsSource == null ? 0 : GetElements(ItemsSource.ElementAt(section)).Count;
        }

        public override UIView GetViewForHeader(UITableView tableView, int section) {
            if (CreateHeader == null)
                return null;

            var sectionItem = ItemsSource.Cast<object>().ElementAt(section);
            return CreateHeader(tableView, section, sectionItem);
        }

        public override UIView GetViewForFooter(UITableView tableView, int section) {
            if (CreateFooter == null)
                return null;

            var sectionItem = ItemsSource.Cast<object>().ElementAt(section);
            return CreateFooter(tableView, section, sectionItem);
        }
    }

}

Had some crashes with an app built on iOS7.1 when running on iOS8.
Looks like that UITableViewHeaderFooterView inner workings has changed in iOS8 (see #148), which resulted in assertions errors in NSObject+PXSubclass.m:63 :

if (![object isKindOfClass:[self superclass]]) {
NSAssert(NO, @"Class %@ doesn't fit for subclassing.", [superClass description]);
return;
}

Any idea?

This line: TableView.ReloadSections(new NSIndexSet((uint)section), UITableViewRowAnimation.Automatic);
Crashes my app only on iOS 9, any ideas how to fix it?